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Title: Collotype and Photo-lithography

Author: Julius Schnauss

Translator: Edwin C. Middleton

Release Date: September 3, 2015 [EBook #49866]

Language: English

Character set encoding: UTF-8

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[Illustration]


  COLLOTYPE
  AND
  PHOTO-LITHOGRAPHY

  PRACTICALLY ELABORATED BY
  DR. JULIUS SCHNAUSS,
  Member of the Imperial German Academy of Naturalists, &c.

  TRANSLATED, WITH THE AUTHOR’S SANCTION AND ASSISTANCE,
  BY
  EDWIN C. MIDDLETON.

  TOGETHER WITH AN APPENDIX ON
  STEAM PRESSES,
  BY THE TRANSLATOR.


  LONDON:
  ILIFFE AND SON, 3, ST. BRIDE STREET, LUDGATE CIRCUS,
  1889.


  PRINTED BY ILIFFE AND SON, 3, ST. BRIDE STREET, LUDGATE CIRCUS,
  LONDON, E.C. WORKS: COVENTRY.




CONTENTS.


CHAPTER.                                              PAGE.

      I. Introductory                                    9

     II. Bichromates in Conjunction with Organic
         Substances                                     12

    III. Summary of the more important Printing
         Processes with Chromated Gelatine              18

     IV. Collotype Apparatus                            25

      V. Chemicals and Materials for Collotype          46

     VI. Preparation of the Collotype Plate             59

    VII. Negatives suitable for Collotype               72

   VIII. Printing in the Press                          88

     IX. Finishing and Varnishing Collotype Prints      96

      X. Other Collotype Processes                     102

     XI. Failures in Collotype: In the Preparation of
         the Plates                                    107

    XII. Investigations on Collotype                   114

   XIII. Collotype in Natural Colours                  119

    XIV. Magic Prints                                  122

     XV. Photo “Glass” Printing                        124

    XVI. Allgeyer’s Collotype Process                  127

   XVII. Practice of Photo-Lithography                 130

  XVIII. Autography                                    135

    XIX. Negatives for Photo-Lithography               149

     XX. Application of the Carbon Process to
         Photo-Lithography                             155

  APPENDIX.

  Steam Presses                                        162




TRANSLATOR’S PREFACE.


The impossibility of obtaining any work in the English language on
the subject of Collotype first led to my translation of the German
work of Dr. Schnauss, and the fact that no work has hitherto appeared
fully dealing with the matter is the excuse I offer for the present
publication. The translation is necessarily one of considerable
freedom, but it is offered as containing all the information to be
found in the original, and in addition, considerable extensions, made
with the author’s consent. The omission of the chapter dealing at
length with the steam machine was necessitated by the fact that the
rotary machine there described is no longer manufactured.

Without pointing to the frontispiece in any sense as a high-class work,
it may serve to show that I have made some practical acquaintance with
the subject. The illustration, printed on ordinary paper, was produced
from the instructions found in this work, and I may add that at the
time of writing I have printed over 500 impressions from the first
plate, and it still remains in fair working condition.

                                                 EDWIN C. MIDDLETON.
  STANMORE ROAD,
    BIRMINGHAM.




COLLOTYPE AND PHOTO-LITHOGRAPHY.

CHAPTER I.

INTRODUCTORY.


The observation by Mungo Ponton of the sensitiveness to light of
bichromate of potassium in conjunction with organic substances is but
little more recent than the discovery of photography itself. If sized
paper is saturated with an aqueous solution of this salt and then
exposed under any transparent design, the latter will be reproduced
as a negative of a brown colour on a yellow ground. If the exposed
paper is placed in water, the bichromate salt will be removed from
the unexposed, and consequently unaltered portions; the image will
remain brown after this treatment, though somewhat bleached. The
sensitiveness to light is proportionately increased by the addition of
larger quantities of organic substances, as starch, paste, glue, sugar
or gum, as first observed by Becquerel. This arises in consequence of
the organic matter being oxidised by the chromic acid, a corresponding
decomposition and reduction of the chromate salt to chromate of
chromium taking place.

In the year 1853 an Englishman—Fox-Talbot, the gifted discoverer of
calotype (_i.e._, the production of photographic negatives on paper
by means of silver salts)—followed up the lines of these important
observations, and discovered that the mixture of bichromate of
potassium and glue entirely lost its solubility and power of swelling
in cold water after exposure to light, and on this he based his process
(heliography) of etching on metal plates. The plate, after receiving a
coating of the chromated gelatine solution, was dried, exposed under
a positive, and afterwards developed or washed out in warm water, all
unexposed and consequently soluble portions being removed, while the
exposed and therefore insoluble portions covered as a negative[A]
the metal plate, and so protected it in those parts from the etching
mordant employed, usually chloride of potassium or perchloride of
iron. His successor in these researches was a Frenchman, Poitevin, who
invested these processes with even greater practical importance. He,
however, worked chiefly on paper with the bichromate mixed with albumen
or gelatine, and attained results which were the first practical steps
towards photo-lithography and carbon or pigment printing. Further on
we shall return with more detail to these subjects. In the hands of
Tessié du Motay and Marechal, of Metz, the discoveries of Poitevin
derived further practical value, and to them we are indebted for the
first advances in collotype, they in their practice using metal plates
as a support. Joseph Albert, of Munich, followed, and introduced
further and considerable modifications, amongst others utilising glass
plates as a foundation. The want of adhesiveness of the chromated
gelatine layer to its support was a source of great trouble to the
earlier experimentalists, and was a matter giving rise to innumerable
difficulties, which were, however, finally surmounted by the researches
of Husnik, Albert, and Obernetter.

  [A] For the production of an intaglio plate the impression on the
      chromated gelatine must be printed from a positive, which will
      naturally give a negative on the copper plate.




CHAPTER II.

THE BICHROMATES IN CONJUNCTION WITH ORGANIC SUBSTANCES.


=Chromic Acid=, now usually known as chromium-trioxide—CrO_{3}—is found
in beautiful red needles, which are slightly deliquescent. According
to the present accepted theory, water containing such crystals in
solution contains the true chromic acid, H_{2}CrO_{4}, which cannot be
produced as crystals. Both the crystals and a concentrated solution
in water give up with facility a part of their oxygen, sometimes with
explosions accompanied by the appearance of fire, and green chromium
oxide, now called sesquioxide, Cr_{2}O_{3}, is formed. Bichromates
of alkalies act in a similar manner, but in a lesser degree. If, for
instance, a few drops of sulphuric acid be added to a solution of
potassium bichromate, and then a little alcohol, or, instead of that,
a piece of sugar be added and moderate heat applied, the solution
will be violently agitated, its yellow-red colour will disappear,
the bichromate be decomposed, and chromium oxide be formed, which,
combining with the sulphuric acid, forms a solution of a violet green
colour. If a sufficient quantity of sulphuric acid be present, the
chromium sulphate and the potassium sulphate combine, forming chrome
alum crystals, octahedron in form, similar to those of ordinary alum,
but of a beautiful dark violet colour. The same are used in both the
carbon and collotype processes. Bichromate of ammonium is easily
decomposed by fire by heating it in a dry state. It will be understood
that in consequence of the decomposition, or rather reduction, of
chromic acid by organic matter, the latter is also decomposed and
oxidised in a corresponding degree. The agent producing this effect may
be either heat or light, or both together; but of special interest to
the collotypist is the action of light upon different combinations of
chromic acid, in the shape of alkali bichromates in conjunction with
organic matters.

=Glue or Gelatine=, in a solution containing about five per cent.
of one of the bichromates spread upon glass plates, and exposed to
light, will, where exposed, become dark brown, at the same time become
insoluble in water, and also lose its power of absorbing the same.
According to the researches of Dr. Eder, this brown substance consists
of chromium chromate and unaltered gelatine. The oxidised portion of
the latter remains soluble and may be entirely removed by treating with
warm water. During the exposure to light formic acid is undoubtedly
formed. Ammonium bichromate, with gelatine, is in the dry state much
more sensitive than the potassium salt; it also decomposes more readily
when heated in the gelatine solution, a matter which must not be lost
sight of in the preparation of the collotype plate.

=Isinglass=—a tolerably pure glutin. In conjunction with the
bichromates it presents the same characteristics as gelatine.

=Albumen=, when mixed with a solution of a bichromate, is not thereby
coagulated, as occurs upon the addition of pure chromic acid. If
poured upon glass and dried it also becomes insoluble in water after
a sufficient exposure to light. This solution is used with great
advantage in photo-lithography, as the unexposed parts are readily
soluble in cold water. The older method, which consisted of using
gelatine in conjunction with bichromate, rendered hot water necessary
in the development of the fatty ink image upon the transfer paper, and
as a consequence of the rubbing at times necessary, the ink, already
softened by the warm water, became smeared, the resulting image
considerably impaired, and the transfer thereby rendered altogether
useless. In collotype a bichromated albumen substratum is still used
by many operators, this coating when dry being exposed _through_ the
glass plate, the latter placed coated side downwards upon a flat
black support, preferably of velvet. After this exposure the gelatine
layer—from which the prints are produced—is applied. This method was
first published by Albert, who originated it. The chromated albumen
solution will not keep long even in the dark,[B] as the albumen
coagulates, and on this account photo-lithographic papers coated with
this solution must be used within a few hours of their preparation.
Such papers are now conveniently prepared with the albumen,[C] and
sensitised as required by floating upon an aqueous solution of one
of the bichromates, to which has been added twenty-five per cent. of
methylated spirit.

  [B] I have found this solution keep a considerable time—a month at
      least.—TRANS.

  [C] I believe Husnik has now discontinued to prepare his photo-litho
      transfer paper with an albumen coating. Recent issues of his paper
      have been simply coated with gelatine.—TRANS.

The chromated gelatine used in collotype may be kept as a jelly in the
dark room, but is better prepared fresh.

Of carbon hydrates only gum chromate is of interest to the collotypist,
its employment being restricted to the “dusting on” process, and the
occasional addition of titles, &c., to the otherwise finished plate.
As with all mixtures of the bichromates and organic substances, it
is only sensitive to light when in a dry condition, and solutions of
it may, without harm, be exposed for some time to diffused daylight.
Aqueous solutions of gum arabic soon become sour and mouldy, and in
this condition are useless for the “dusting on,” or, in fact, any other
photographic process. As a preventive a few grains of sulphate of
quinine may be added, which will preserve it effectually, and is quite
inert in photographic operations.

This solution applied to glass and dried is, in its dry condition,
extremely sensitive to light. If printed under a negative, and then
exposed to a damp atmosphere, it absorbs moisture, and becomes “tacky”
upon the portions fully protected by the densest portions of the
negative, while the parts exposed under the clear glass of the negative
will be free from any such tendency. The gradations of the negative
between these two extremes will be represented by the surface of the
gum being more or less adhesive, and it is this property which renders
it valuable in various processes. After exposure under a negative
finely-ground colour—for instance, graphite—is carefully dusted over
the surface of the plate by means of a camel-hair brush, and the
powder will adhere in exact proportion to the protection afforded by
the negative. A picture is thus produced in graphite powder possessing
all the gradations of the original. From a negative a second negative
is produced, while from an exposure under a positive a positive will
result, each, however, reversed as regards left and right when compared
with the original. Advantage is taken of this process to produce
reversed negatives, a subject more fully dealt with in another chapter.

=Bichromate and Sugar= are never used alone, but as an addition to
heighten the sensitiveness and increase the hygroscopic properties of
the gelatine or gum-chromate solutions. By the addition of sugar and a
little ammonia to chromated gelatine the solubility of the gelatine in
hot water is increased. The addition of acetic acid instead of ammonia
acts in a contrary direction. It is advisable to become acquainted with
the action of certain substances, the application of which to the
printed layer increases its solubility after exposure to light, and
of others having a contrary or hardening influence on the same, such
oft-times proving of service in the case of under or over exposure. To
the former class belong all alkalies, as chloride of lime and cyanide
of potassium; while among the latter, which have a tanning or hardening
effect on gelatine, may be particularly mentioned tannin, alum, chrome
alum, and chloride of zinc.

=To remove spots=, which print dark, from collotype plates a solution
of chloride of lime is used. To produce dark spots without exposure
to light a solution of tannin is used, which is also available for
adding descriptive titles or other matter to the plates. The ink will
“take” as well on the spots or parts touched with the tannin solution
as if exposed to light. A collotype plate which has been prepared for
printing from may also have writing executed upon it with a bichromated
gum solution, once more exposed to light, the writing will then readily
take the ink, and appear in the impression as a black inscription.

Gum chromated solutions reduced to proper proportions, and applied to
different textures and the same subsequently exposed to the light,
render them completely waterproof.




CHAPTER III.

SUMMARY OF THE MORE IMPORTANT PRINTING PROCESSES WITH CHROMATED
GELATINE.


These processes are all based upon the change in the hygroscopic
properties of chromated gelatine brought about by the action of light,
which renders the parts exposed insoluble.

=Carbon or Pigment Printing.=—In this interesting process finely ground
colouring matter is added to the solution of chromated gelatine, and
spread upon paper; or the paper may be coated with the gelatine and
pigment, and afterwards excited by immersion in a solution or bath
of one of the bichromates. If, after drying such paper or tissue, it
be exposed under a negative in an ordinary printing frame, and then
immersed in warm water (90° to 130° F.), the water will dissolve only
such portions as may not have been affected or hardened by the action
of light through the negative, while the parts that have been exposed
to its action will be insoluble, and remain attached to the paper
support, forming a positive picture. Images produced in such a manner,
however, are devoid of half-tone, and this procedure is only suitable
for line subjects, while even for such the paper must have been very
evenly coated, or portions of the picture may be washed away. For
the production of half-tone subjects it is necessary that the picture
be developed _from the back_. This may be effected by transferring
the printed tissue, after first soaking in cold water, to a surface,
usually either of paper or glass, and developing it in contact with,
and allowing it to remain upon, such surface. This procedure is
known in carbon printing as single transfer. Unless the negative be
a reversed one—or a film printed from the reverse side—the resulting
print will be subject to the disadvantage of being reversed as regards
left and right. In cases where ordinary negatives have to be used,
and this reversal cannot be tolerated, it is overcome by the “double
transfer” method of printing, the print in such cases being developed
upon a so-called “temporary support,” and again transferred to its
“final support,” when it appears as a non-reversed image in permanent
pigment.[D]

  [D] For further details of this interesting process see the “Autotype
      Manual,” by J. R. Sawyer; or Liesegang’s “Carbon Process.”

=The “Powder” Process.=—Take, instead of gelatine, a solution of
gum arabic and sugar, to which is added a solution of bichromate of
potassium or ammonium. With this a glass plate is coated, dried, and
exposed under a negative, if it be desired to produce a negative; or,
if a positive be desired, the exposure must be made under a positive.
After a short exposure the plate is dusted over with a powder in an
extremely fine state of division, such as graphite if for negatives; if
for burnt-in enamels, a specially-prepared enamel, ground extremely
fine, must be used. Such powders will only adhere to the plate in
exact proportion to the action of the light during the exposure in the
printing frame, and a reversed copy of the original will be produced.

=Collotype and Glasstype.=[E]—In these processes the printing depends
upon the property possessed by the bichromated gelatine film, which has
been properly exposed under a negative, of absorbing water in varying
proportions, in exact accord with, but in inverse ratio to, the action
of the light. The application of a roller charged with fatty ink of a
suitable consistency, will deposit upon the gelatine surface a layer
of ink in exact proportion to the action of the light and in inverse
proportion to the amount of water absorbed by the film. In this manner
a picture is produced in ink which by printing is transferred to paper,
and will exhibit all—even the finest—gradations of light and shade.

  [E] Glasstype, more fully described later on, has never been practised
      commercially in England.

=Woodburytype.=—If an especially thick film of gelatine, containing a
small proportion of pigment, be sensitised, exposed under a negative,
and subjected to prolonged soaking in warm water, a picture exhibiting
considerable relief will be obtained, which, after drying, may, by
pressing into lead or treated by the galvanoplastic method, yield
a matrix from which casts may be produced in a coloured gelatine
solution, or ink, which is poured into the mould; on this is placed
a waterproof paper; the press, which is of special construction, is
closed, and the ink allowed to set; the paper is then removed, bearing
upon its surface the printed Woodburytype, which is hardened by alum,
and then scarcely distinguishable from a silver print.

=Stannotype= is a modification of the last-described process by the
same inventor. A positive is first produced from the original negative,
and from the positive a print is made on a thick gelatine tissue. This
is developed by long washing in warm water, the resulting relief being
a negative; this is coated with tinfoil of extreme thinness, and used
as a mould for printing from with the gelatine ink, as previously
described. This obviates the use of hydraulic pressure and special and
expensive appliances.

=Heliogravure; Photogravure.=—If, instead of printing from the Woodbury
mould in the gelatinous solution, a fatty ink is used, the process is
known under these titles. The exact methods of roughing the depths of
the plates to facilitate their retention of the ink are regarded as
secrets by the most successful operators.

=Photo-Lithography and Photo-Zincography.=—In dealing with a subject
in lines, dots, or stipple, a paper may be coated with a solution of
chromated gelatine, dried, exposed under a suitable negative, coated
with a film of fatty ink, and allowed to soak in cold or tepid water;
this, penetrating the unhardened portions of the film, causes them
readily to part with the ink, which, however, adheres tenaciously
upon the hardened portions, representing the picture. This image, when
properly cleared, may be transferred to stone or zinc, and printed
from in the lithographic manner upon a suitable press, or if the image
upon the zinc be etched into relief by the process known as Gillotage,
and mounted on a wood block of suitable height, it presents a printing
surface which may be used in conjunction with type.

=Gelatinotype.=—It has long been felt as a desideratum to make use of
the photogenic properties of the gelatino-bichromate for letterpress
printing, _i.e._, to find out a simple and satisfactory method by which
collotype plates could be transformed in letterpress printing plates.
There have been made many attempts in this direction, but hitherto
without any practical results; the difficulties seemed to be too great.
Recently, however, Professor J. Husnik, of Prague, has overcome these
difficulties, his new patented process, called by him “Leimtypie,”
that is to say, Gelatinotype, being one of the greatest practical
value, quick, cheap, and giving most satisfactory results. The process
consists in the production of high relief blocks in gelatine. Husnik
exposes a gelatino-bichromate tissue under a negative, and then
develops the relief picture in a peculiar manner.

The method consists in the application of a saturated solution of
bichromate salts for developing, a new and previously unknown property
of the chrome salts thus coming into employment. These salts, in
comparison with the acids, have the advantage not only of dissolving
all unexposed gelatine during development, but also in hardening the
already exposed parts of the picture upon the copy to be developed, the
impression received from the light being increased by contact with the
chrome salt solutions. In this way the relief can be developed a longer
time, and becomes deeper.

Another new phase is the manner of the second development. The first
development is interrupted before the fine parts have been injured, the
relief allowed to dry, the white parts (the sub-ground) covered with
printing ink diluted with turpentine, using a fine brush quite near to
the lines, and then the whole relief exposed once more to light. The
relief, on account of its having taken up much chrome salt during the
first development, is very sensitive to light, and hardens not only on
the surface, but also on the sides of the lines. After removal of the
black ink it can be developed to any depth, particularly if the larger
white parts have before been cut out with a knife.

This process has lately been further improved by the inventor, by the
use of gutta-percha films, which are placed between the gelatine film
and the zinc plate on which the gelatine relief has to be fastened.
This is effected as follows:—The zinc plate, after having been well
cleaned and rubbed over with emery paper, is coated with a gutta-percha
solution and dried. It is then heated to about 212° F., and allowed
to cool. During this cooling process the bichromated gelatine film,
before being developed, is laid on at a temperature of between 111°
and 77° F., whereby the hardening gutta-percha film secures a perfect
combination with the zinc plate. When this has been done the gelatine
film is developed in the above described manner to a relief. By this
improvement the gelatine blocks become so solid that they will yield
more than 50,000 prints in the printing machine without being injured.




CHAPTER IV.

COLLOTYPE.—APPARATUS.


Before commencing any practical work it will, of course, be necessary
to procure various utensils and material not usually found in the
photographic studio. All these should be procured from reliable dealers
and of the best quality, for the evil consequences of false economy
will make themselves felt in endless failures. The best to be obtained
are none too good for collotype. In the practice of photography the
whole success depends on a series of apparent trifles, and the same may
be said to hold good, but in a far greater degree, in this process,
which is one in which the difficulties can scarcely be overestimated.

The photographer will most likely be already in possession of many
pieces of apparatus he may utilise—for instance, dishes. The best
and dearest are those of china; but for many—in fact, most—collotype
purposes, those of tin or zinc may be used.

For warming or cooking the gelatine solutions tin vessels are the
handiest, as they easily conduct the heat and are unbreakable. Although
the chromated gelatine may remain in them for a short period without
harm, it is not advisable to allow it to do so for any length of time,
but to remove the solution and wash the vessel thoroughly with hot
water, and at once carefully dry, otherwise they will soon corrode,
and contaminate the gelatine solutions. The best utensils to use are
wide-mouthed shallow jugs, as they are easily kept clean, and in them
the chromated gelatine solution keeps well, and with their use no fear
of decomposition need be entertained.

=Filtering= the gelatine solutions is a somewhat troublesome matter,
and should be effected at a high temperature and as quickly as
possible. The simplest method is to procure a piece of perfectly clean
flannel of suitable size, thoroughly moisten it, and insert into a
brass ring, which is provided on the outside with small barbel hooks,
to which the flannel is fixed, as in the retinaculum of the chemist.
The ring is provided with a clip and handle, by the former of which it
may be attached to a vessel of almost any size, and the latter is a
convenience in holding it over plates to which the gelatine has to be
applied. A careful filtering is obviously essential to the production
of clean plates. Many complicated filtering appliances have been
devised for gelatine and other solutions difficult of filtration, as,
for instance, those of albumen or gum. Baron Szretter describes in the
“Photographische Correspondenz,” 1878, an apparatus constructed by him.
It consists of two vessels, an upper and a lower one, which by means of
longer or shorter tubes communicate with each other in accordance to
the stronger or weaker pressure required by the liquid to be filtered.
Soldered round the upper rim of the lower vessel is a ring of sheet
brass, about two to three cm. in width; over this ring the filter paper
is placed, which again is covered with a piece of strong felt enveloped
in flannel. To prevent the liquid escaping round the sides of the
ring a strong iron ring is applied, which by means of a screw presses
against the felt so that no space exists between the ring and the
paper. To prevent the pressure of the liquid forcing the felt out of
position, and so tearing the paper, a metal wire gauge is used to keep
the felt in place. The liquid placed in the upper vessel passes through
the tube into the lower vessel through the paper and felt layer. When
it is necessary to warm the solution to be filtered, as in the case
of gelatine, the whole apparatus is covered with an outer covering,
and on the other side a pipe is applied for the purpose of effecting a
circulation of the heated liquid, which is thus kept constantly rising
through the one pipe and returning through the other.[F] Heat is
sustained at an even temperature during the whole operation by means of
a small lamp. A simple method of filtering such solutions is to pass
them through purified sheep’s wool, or spun glass, a quantity of which
is placed in the tube of the funnel. The whole apparatus may be placed
in a warm oven during the process, or the drying box may be utilised
for the purpose.

  [F] [Illustration: _Fig. 1._]
      The above description not perhaps being perfectly clear, and
      having been unable to obtain any further description, I give a
      sketch (_Fig. 1._) of an apparatus found to answer well for the
      filtration of gelatine solutions and other viscid bodies. =A= is
      a glass flask, =B= a rubber stopper, =C= a funnel containing a
      filtering medium of washleather, =D= a tube attached to a
      three-way cock =E=; one hand manipulates the latter, while
      the other works the piston =F= of a syringe =G=.—TRANS.

=Printing Frames= of different sizes will be found to hand in the
photographic studio, and may be utilised without alteration for
printing the collotype plates, if they are deep and strong enough to
bear the necessary pressure, which is usually applied through the
medium of springs; these are better removed, and wooden wedges inserted
in their stead between the cross-bars and the loose wooden back of the
frames, as by these means far more pressure may be applied. By lifting
the one half of the hinged back of the printing frame an examination by
transmitted light of the collotype plate may be made and an experienced
operator will in this manner judge the exposure of the plate.

=The Actinometer= is, however, recommended, particularly for a
beginner, as it greatly aids in forming a correct idea of the exposure.

=The Drying Box= is of great importance to the successful working of
the process. The opinions of the various practitioners with regard to
the temperature at which the drying of the plates should be effected
differ as widely as upon the advisability or otherwise of admitting
a current of air through the box during the operation. The drying
should be completed as rapidly as possible from the commencement of
the operation, care being taken that the heat never exceeds 50°C. Many
plate-makers simply dry the plates in an open apartment—of course,
only illuminated by a non-actinic light—simply placing the plates
on a horizontal surface, which may be maintained at the temperature
indicated by a water bath, a lithographic stone, or merely a cast-iron
plate arranged in a suitable manner for heating from below. This
method of drying is open to many objections: the surface of the plate
is seldom free from dust, and the gelatine coating is too liable to
irregularities from draughts admitted to the apartment during the
process. They are more frequently dried in specially-constructed boxes
provided with screws for accurately levelling the plates, and through
which only a small circulation of air takes place. These boxes are
usually rectangular in shape, the upright sides being of wood and the
bottom of sheet iron. The lid is an open framework covered with a
close orange or black cotton material, the whole standing upon four
iron legs over a spirit or gas flame. In the upper part of the box a
thermometer is fixed, about the centre of either the side or lid, in
such a position that it may be readily observed without the necessity
of opening the box. Strong horizontal iron bars are placed across
at about the centre, and are provided with thumbscrews, upon which
may be placed a plate of glass bearing a circular spirit level, by
which means the plates may be levelled with the greatest accuracy.
The sheet-iron bottom of the box being heated unevenly, it becomes
necessary to mitigate this inconvenience as far as possible, which is
easily done by covering the plate to a depth of about half-an-inch with
dry river sand, over which should be placed tissue paper to keep down
any possible dust.

[Illustration: _Fig. 2._]

=An Automatic Regulator= of practical value is that devised by
Ruegheimer. It consists of a glass tube, =A=, =A¹=, =A²=. =A¹= is
closed with an indiarubber stopper, through which passes a glass tube
=B=, the lower end of which is cut off at an angle. It is attached
to the gas supply pipe. The tube =C= is connected to the burners. To
=D= is attached, by means of rubber tubing, a glass bulb =F=, which
is placed inside the drying-box. =G G= is mercury, and =H= a rubber
stopper by which the pressure on the mercury and quantity of air in =F=
may be regulated. The action of the instrument is obvious. The gas
passes down =B=, over the surface of the mercury and by the tube =C= to
the burner. On the bulb =F= reaching a certain temperature, the mercury
will allow just sufficient gas to pass from the tube =B= to maintain
the box at a given heat. If it should fall, the mercury recedes from
the aperture of the tube =B=, a larger quantity of gas passes to the
burner, and the temperature is restored to a normal degree. If the air
in the ball =F= expands to too great an extent, the mercury rises,
and would eventually entirely close the aperture and cut off the gas
supply, unless the tube =B= is provided with a small hole acting as
a by-pass. The tube =B= may be moved up and down through the rubber
stopper at =A¹= as a means of adjustment.

[Illustration: _Fig. 3._]

M. Thiel, of Paris, uses a very convenient drying-box, which, with his
permission, is here explained. In a brick-lined receptacle under the
laboratory floor lies the water-heating apparatus, which is constructed
of sheet copper, and is capable of containing about four litres of
water, utilised in the production of steam for heating the box. _a_,
fig. 3, is the pipe passing through the wall into the drying-box;
_b_ is the gas supply pipe to the two atmospheric burners. Fig. 4
represents a plan of the drying-box; _c c c c_ the perpendicular sides
of the same, _a a a_ gives a plan and position and arrangement of the
earthenware heating pipes lying in a serpentine form at the bottom of
the box, entirely covered with dry sand, and this again covered, as
before described, with tissue paper. _b_ is the outlet of the steam
pipe. _d d d d_ are movable horizontal iron bars with adjusting screws,
on which the plates are levelled. The box is covered by a hinged lid,
which is raised about a couple of inches during the drying to allow
the air to circulate. The dimensions of the box will be determined by
the size of the plates to be used, several of which may be placed side
by side. Its height is about half a metre inside, and the plates are
placed about its centre.

[Illustration: _Fig. 4._]

=Glass Plates=, to be used for printing from, must as a first
consideration have their surfaces ground quite true and parallel.
Since the introduction of special collotype presses requiring less
pressure, the thickness is of less consequence than formerly, but for
convenience of handling and to withstand the necessary pressure, in the
printing frames, plates of at least four millimetres in thickness are
desirable. Many use them from 8 to 10 millimetres in thickness; this,
in the larger sizes, means a weight both inconvenient and difficult to
handle. It is probably easier to work upon plain glass surfaces, and
since means have been discovered of causing the chromated gelatine to
adhere to polished glass with sufficient tenacity to produce several
hundred impressions, the employment of ground glass plates is much more
a matter of choice than formerly. The ground surface, however, assists
the formation of a grain in the case of thin layers, and the operation
of grinding serves to remove accidental scratches from the surface of
the plates. As in practice these damages constantly arise, it will
in the long run be found both desirable and economical to employ the
ground plates.

=Ink Rollers= are also of great consequence in both collotype and
lithographic operations. For printing from stone leather rollers have
always been exclusively employed, and they are still used in some
collotype establishments, more particularly where hand presses are yet
worked.

=The Leather Roller= consists of a wooden cylinder or stock of about
21 to 42 cm. in length and 9 to 11 cm. in diameter, with handles at
either end, usually turned in one piece with the cylinder. Boxwood
handles are sometimes let into the ends of the cylinder, but although
smoother to work, they not infrequently work loose. In using these
rollers the handles do not come in direct contact with the hands, but
are covered with a protection of stout leather, which not only protects
the printer’s hands from heating, but enables him by a heavier or
lighter grip of the handles to apply a heavier or lighter pressure of
the roller—a point of great value in inking the plate.

The wooden stock of the roller is first covered with a double thickness
of woollen material—flannel or Melton cloth—and over this is drawn the
cover of calf-skin, flesh side outwards. The manipulation of the seam
must be managed with extreme care, as any unevenness would render the
roller useless. At both ends of the cylinder the leather projects,
and is usually drawn tight with string or nailed on. There are two
descriptions of leather rollers—smooth and coarse. The latter are only
used to apply ink to the stone or plate, and then, with the smooth
roller, the proper distribution of the ink is effected. For the latter
purpose, in collotype, hard glue or indiarubber rollers are employed,
being considered far preferable. When a leather roller _is_ in good
order, and its use has been thoroughly mastered, it is looked upon by
many printers as indispensable. A serious disadvantage is that when new
they are almost unusable for collotype, and after prolonged use the
leather stretches, they become wrinkled, and this, of course, affects
the even distribution of the ink. A new leather roller needs a special
preparation or “breaking in” before it may be considered fit for use.
It should be well saturated with a fatty matter, a very effectual way
of doing which is to roll it well at intervals in a moderate supply
of thin varnish as used for thinning printing ink, this process being
persevered with so long as the roller continues capable of absorption.
A better but more troublesome method is to roll the rollers twice daily
in thin varnish, continuing the operation for a week, at the end of
which time the roller may be well rolled upon the inking slab in stiff
black printing ink, the superfluous ink being occasionally removed from
both the roller and slab by scraping with a blunt knife, and a fresh
supply of ink applied. This troublesome and tedious operation should be
continued for a period extending over several weeks until it has become
quite smooth and even, though it will still be found better to use it
only for common work, or, if possible, on stone. To keep the roller
in good condition it should, on each occasion after use, be carefully
scraped with a clean, smooth-edged knife—not too sharp. Some practice
in this operation is required to avoid cutting the leather. Great care
should be taken to avoid this, the blade of the knife being held almost
flat upon the roller during the process. The scraping should always be
in one direction, to ensure which it is advisable to place a mark upon
one of the handles.

Unless these precautions be observed the ink will dry in, and
completely spoil the leather. If not to be used again for some time
tallow should be carefully and thoroughly rubbed into the surface of
the roller as a preservative, but before again using this coating must
be removed either by means of a knife or washing with turpentine.

=Glue Rollers= have long been in use, but chiefly for letterpress
work and steam machines in general. A soft composition of a very
elastic nature is quite useless for collotype; its substance must, on
the contrary, be tolerably hard, and of a brown colour, as usually
employed on the steam letterpress jobbing machines. For hand rollers
for collotype it is preferable to have a strong iron frame with double
handles, as used by letterpress printers. Such rollers are preferable
to those of leather, and will answer perfectly for laying on the first
stiff ink, and also for rolling up the half-tones. To clean they
should on no account be scraped, but simply washed with turpentine,
and on this account are much easier cleaned than leather rollers.
Schaarwächter gives the following as an excellent composition for
collotype rollers: Brown glue, three parts, steeped for two days in
cold water. The pieces should then be dried in a cloth, and afterwards
dissolved. When melted add, with constant stirring, one part of
treacle, which has been previously boiled, allow the whole to boil,
and skim. The composition is then run into a thin copper cylinder or
mould, which must be polished smooth, clean, and well oiled; and in the
centre of which has been placed the wooden cylinder or stock. After
cooling, the roller is pushed out of the mould, and washed with alcohol
or turpentine to remove any trace of greasiness due to oiling the
mould, placed in a bath of tannic acid, washed with water, and dried.
The composition rollers, as used in typographic printing, are made with
glycerine instead of treacle, and may be used for collotype if not too
soft.

=Indiarubber Rollers= are more expensive, but possess special
properties rendering them particularly suitable for photo-lithography.
In construction a wooden stock with suitable handles is covered with
very thick well-vulcanised indiarubber, which has a fine smooth
surface, rendering it easy to clean by means of turpentine. If it
becomes “tacky” on the surface it should be well rubbed with French
chalk, or soap-stone, which will readily absorb the turpentine,
but this coating must be thoroughly removed before again using the
roller. An excellent suggestion appeared in one of the polytechnical
periodicals, that the rollers should before use be coated with a
solution of pure or bottle rubber in benzole or bisulphide of carbon
after having been well washed with turpentine.

These indiarubber rollers are not suited for the first inking of
the plate, but are invaluable for rolling up the half-tints of the
collotype plate. As they somewhat readily take colour off the plate
they must be first rolled up in a thinner ink and a separate slab.
According to “Lithographia” these indiarubber rollers may be cleaned
with lye, or strong alcoholic spirit. If cleaned with turpentine it may
be advantageously followed by rinsing with soap and water; by so doing
the application of French chalk is unnecessary. These rollers are, by
comparison with others, nearly indestructible, and therefore cheap,
notwithstanding their high first cost.

[Illustration: _Fig. 5._]

=Velvet Rollers= have latterly come much into use, and are very
successfully used for inking-up the transfers in photo-lithography.
They may be also used in photo-xylography and photo-ceramic processes,
and also for certain purposes in collotype. A necessary precaution
is that the seam of the velvet should always be kept off the surface
subjected to the rolling, and this may be carried out if the roller
is, say, 10-1/2 centimetres in diameter, a length of 31·2 centimetres
may then be rolled without using the seam. The sketch will explain the
construction. The cylinder or stock is of pear-wood, and the handles of
box; first covering serge, which before sewing on should be well shrunk
in hot water; over this comes the velvet, the edges of which must not
overlap, but must be drawn together as close as possible by means of
thread. One advantage of this roller is that it is ready for immediate
use; it must, after use, be carefully cleaned before being placed
aside; this is best done by repeated rollings on a clean slab, and the
judicious application of a little turpentine. Turpentine only may be
used to thin ink for use with this roller.

=Drying Rollers.=—In addition to those already enumerated, all of which
are intended for the application of the ink to the plate, other rollers
are required, similar in construction, but covered with wash-leather
or cloth, and used for the purpose of absorbing superfluous moisture.
For these it is necessary, or at least advisable, that the frames be so
constructed that the rollers may be readily removed when by continued
use they have become too damp. This method of drying the plates is
far preferable to the customary one of wiping with a cloth, for even
with the greatest care, if the printing should extend over hundreds of
copies, the layer upon the plate will inevitably get scratched when
wiping or rubbing is resorted to, especially if isinglass—which tends
to soften the film—be present.

=Palette Knife or Spatula.=—It is unnecessary to describe; they are
used for mixing the ink and applying it to the slab and rollers, and
for cleaning the latter. They may be either of hard wood or metal.

=The Ink Slab= may be either of slate, a lithographic stone, or a sheet
of strong zinc securely attached to a block of wood truly planed.

=The Press= is an indispensable requisite for printing operations.
There are small wooden hand-presses, especially constructed for
collotype, which may be purchased at a very low price—£4 to £5; but
the more economical way is to procure a small lithographic press
constructed of iron. This will not only be found more durable, but it
may, if occasion arise, be used either for lithographic or zincographic
printing, as it will bear the necessary pressure, which is greatly
in excess of that applied in collotype printing. The hand-press
constructed by Sutter is a form that may be strongly recommended. If
the output of prints is to be large, a steam machine will be necessary,
the cost of which will be not less than £200 to £250. Fig. 6 represents
a press which has been largely used for collotype. =D= is the bed or
carriage upon which the plate is fixed in the manner described further
on. By turning the crank handle =C= the bed is carried under the
scraper, which is secured in the scraper-box =A=. The scraper is kept
in position by the lever =B=. The scraper-box is represented as closed
down in the illustration, but in actual practice it would not be in the
position shown until the tympan-frame =E= had been lowered.

=The Tympan=, of either leather or thin sheet zinc or brass, is marked
=F= in the illustration. All iron portions of the press subject to
friction should be frequently cleaned and carefully oiled with a good
machine-oil.

[Illustration: _Fig. 6._]

=The Scrapers= should be of either pear tree, lime, maple, or
preferably box, with a blunt bottom edge, which should be planed true,
and finally finished by rubbing on a sheet of glass-paper placed upon a
perfectly flat surface. They must be adjusted with even more precision
than is necessary in lithography, as owing to the difference in the
printing surface, the same pressure cannot with safety be applied. With
plates or stones of large size it will be found that the pressure of
the scraper will be unequal, greater pressure being exerted in the
centre than upon the edges of the printing surface. Many printers,
to counteract this tendency, slightly scrape away or hollow out by
means of a piece of glass the centre of the scraper. With sufficient
pressure and plenty of elastic packing between the printing paper and
the tympan, this slight difference may be easily overcome. Several
scrapers should be provided of various lengths, so that one of suitable
size may be always available to suit the particular work in hand. It
should always be slightly longer than the width of the picture, but
shorter than the width of the stone or plate. By pressing the edge of
the scraper to the surface of the latter and looking towards a window
no light should be visible between the two surfaces. If the edges of
the scraper are carefully rounded, it may be covered with a strip of
wash-leather,[G] smooth side outwards, and secured by means of tacks,
by which arrangement the pull will be easier, the impression more even,
and the tympan and scraper will last longer. The accompanying sketch
represents one of Poirier’s special collotype presses, constructed
entirely of iron. The details are so clearly shown in the engraving
that after the description already given it will be unnecessary to
point out further details.

  [G] This is necessary only with metal tympans.

=White Margins to Pictures.=—To facilitate the production of pictures
with white margins, instead of using a mask of paper either oiled
or treated with a varnish, an arrangement has been introduced, as
represented in fig. 7, the design of which is due to Mr. Raph.
Schlegel. The drawing is not perspectively correct, but is made to
show as clearly as possible the arrangement and manner of working.
The scraper—not shown in the illustration—works on the tympan =O=.
=A=, carriage or bed of the press, carrying the printing plate. =B=,
a slide of light wood. This prevents the frame =D= and the printing
paper =M= coming in contact with the plate before the impression is
actually being taken by the scraper. The wooden slide bridges over the
plate, and may be 15 to 25 millimetres higher than the plate itself.
When the rolling up or inking of the plate has taken place the slide is
pushed so far forwards as to allow only just sufficient room for the
scraper to rest upon the plate. The action of the scraper during the
taking of the impression causes the slide to work out, and allows the
paper to come in contact with the print layer. =E E= are adjustable
buttons to regulate the traverse of the carriage when printing. =D= is
a second frame necessary to carry the strips of thin zinc, =Ef Ef, Eg
Eg,= which entirely protect the edges of the paper to be printed upon,
and so produce an impression with a white margin. These strips may be
almost instantly adjusted to give any required size. The frame =D=
must be so much smaller than the frame =L= as to be easily covered by
the latter, allowing for the projecting screws and nuts of the clamps
=f=. The zinc strips should be reduced to a feather edge on the sides
next the picture, and should have secured to them strips of fine paper
(foreign letter-paper), which should extend over the edges about
three millimetres, to prevent damage to the gelatine layer. =f f= are
clamps for the zinc strips =Ef=. They are put through the slots, and
the tension adjusted by the nuts. The zinc strips are perforated by
two holes at each end, and secured to the clamps by means of screws.
=Eg= are also zinc strips; =g= clamps provided with two holes, in
each of which a hook is inserted. Corresponding with these a second
pair of hooks are inserted in holes in the frame =I=, the hooks being
connected together by the strong indiarubber bands =h=. This gives to
the strips =Eg= a certain amount of elastic tension. The clamps =K=
are also adjustable in slots, and similar to =f=; =L=, frame for the
reception of the tympan; =M=, large clamp for stretching the elastic
sheet =O=; =N=, zinc tympan, greased to facilitate its movement under
the scraper, it also prevents grease penetrating the sheet =O=; =P=, a
bracket on bed =A=, against which the tympan frame rests when raised
and thrown back. The arrangement is used as follows: When the plate
has been satisfactorily inked or rolled in, the slide or bridge =B= is
adjusted over the plate, leaving a strip of about three _mm_. uncovered
to allow of adjustment of the scraper. Lower the frame =D= in which the
zinc strips have been adjusted to the size of picture; the printing
paper is placed over this slide, and covered with a few sheets of paper
backing. The tympan frame =L=, together with the sheeting and greased
zinc plate, are lowered upon the work, the scraper adjusted, and an
impression taken.

[Illustration: _Fig. 7._]




CHAPTER V.

CHEMICALS AND MATERIALS FOR COLLOTYPE.


=Gelatine.=—The basis of the Collotype process is gelatine—the finest
purified animal glue—and the important part it plays in the process
demands an acquaintance with its properties, which are found to differ
widely, according to its origin and method of preparation. Gelatine
suitable for Collotype should be free from all impurities—particularly
alum, which is not infrequently added in small quantities during
manufacture. Dr. Eder, in particular, has made most minute examinations
of various samples, more especially with regard to their suitability
for Collotype, Carbon, and the Galvanographic processes, and his
opinion, agreeing with that of other experimentalists, is here quoted:—

The two principal modifications of gelatine are those produced from
bones, sinews and skins of animals, and from the air bladder of the
sturgeon, the latter variety, better known under the name of isinglass,
represents, from a chemical point of view, glue in the purest form.
On account of its high price and ever-varying quality as found in
commerce, it must in practice give place to a glue or size containing
chondrin, and prepared from bone and gristle. Another objection is,
that plates prepared with an admixture of isinglass are less durable
than those containing gelatine only. On the other hand, it certainly
possesses advantages of its own, which will be more fully considered
hereafter. A gelatine suitable for collotype must absorb plenty of
water and swell out, but not liquefy after having been soaked in cold
water for twenty-four hours. Gelatine or isinglass prepared from the
bladder will not stand this test, but, on the contrary, partially
disintegrate. The consistency and bearing capacity of a jelly formed
by dissolving gelatine in water by means of heat and allowing it to
cool, form, in the opinion of Lipowitz, a safe and reliable means of
forming a judgment as to its suitability for collotype. Dissolve by
first soaking five grammes in 45 cm. of distilled water for several
hours, afterwards apply heat, and allow to stand twelve hours to set.
For purposes of comparison this should always be done in a glass of the
same diameter. A small tin or zinc slip is placed across the top of
the glass vessel containing the jelly; through the centre of the tin a
hole is pierced, through which a wire moves easily up and down. To its
bottom end is soldered a piece of tin, of about 15 cm. diameter, the
convex side lying upon the surface of the gelatine. On the other or
upper end a small funnel is placed, large enough to contain 1-1/2 kilo.
of small shot. The weight of the wire and funnel being ascertained,
it will be a simple matter, by also weighing the shot, to calculate
the weight required to sink the instrument into the jelly, and to
ascertain with accuracy its weight-bearing capacity and proof of the
relative value of various samples for Collotype printing. If otherwise
suitable, the variety capable of supporting the greatest weight
before yielding will be the one to select. The power of absorption
of different samples varies considerably; for example, the Collotype
gelatine of Creutz absorbs in two hours 30 parts of cold water poured
over it. Nelson’s patent opaque, in the meantime, only absorbs five
parts, but after a further period of 4-1/2 hours the difference is
equalised, as it will absorb 25 parts more of water, making altogether
exactly 30 parts. This experiment proves the latter to be a harder
quality than that of Creutz, and it necessarily requires a somewhat
different treatment for the production of the best results.

=Isinglass= or fish glue, although, as before stated, a finer quality
of glutin than the ordinary gelatine of commerce, is, on account of its
high price and varying quality, comparatively little used. The addition
of this substance also softens the gelatine layer. On the other
hand, it possesses certain properties which render its use at times
desirable; for instance, it does not dry so completely as gelatine,
the layer prepared with it consequently gives cleaner and more even
proofs, a point particularly noticeable in the earlier impressions.
Such prints will also exhibit greater brilliancy, and this is of
especial consequence in work produced from photographs from nature,
in which class of work the half-tones are too often wanting. Some
operators take even equal parts of isinglass and gelatine, but such
layers must be very thin, and dried quickly. Thick layers are liable
to crack or fly, and in use to refuse to take the ink, which must for
such film be used in greater quantity and thinner than when gelatine
alone is employed. A solution of isinglass is not so readily prepared
as one of gelatine. It is necessary to allow it to soak in cold water
for from twelve to twenty hours, and the temperature then gradually
raised to nearly boiling point, at which heat it should be maintained
for some time longer, and then filtered through flannel into the
gelatine solution. In printing from these plates, particularly when the
proportion of isinglass exceeds one-third the amount of gelatine, there
is a disagreeable tendency of the printing paper to adhere in the high
lights—that is, in those parts of the print layer which are represented
in the negative by entire opacity—as in the sky of a landscape or a
background which has been “stopped out” on the negative. On other
portions of the plate where the light has more fully acted—during the
printing in the printing frame—this troublesome defect will not be
observed. The fault is more noticeable when the dull enamel paper is
used, while a hard, well-sized letter paper presents the other extreme.
Further details of printing papers will be found in another chapter.

In the introductory chapter of this work the photo-chemical
qualifications of the bichromates of ammonium and potassium with
regard to collotype are considered.

=Bichromate of Potassium= is found in the well-known rich orange-red
crystals. It is readily soluble in cold water (1.10). It may be easily
recrystallised and purified readily out of either a hot, warm, or
cold solution, and forms in thin layers of fine crystals. Therefore,
in using it for collotype, care is needed not to exceed the strictly
necessary proportion, as the plate may be hopelessly spoiled by the
partial crystallisation of the salt, which will probably show during
the process of drying. The maximum addition of bichromate of potassium
in proportion to the weight of the gelatine may differ according to
the peculiarities of the latter. Dr. Eder considers about 3/10 to 4/10
by weight of this salt in a dry state may be added to a gelatine,
which will absorb from six to ten times its weight of water, without
fear of crystallisation. There are, however, many gelatines that are
incapable of working with more than 2/10. Rapid drying of the plate in
a current of air, and at a temperature of 40° C., will, to some extent,
obviate this objectionable feature. By reason of its comparative
insensitiveness to light and this facility of crystallisation, and
notwithstanding its comparative low price, it is now far less used in
collotype than

=Bichromate of ammonium=, the crystals of which somewhat resemble
those of the potassium salt. In colour they are of a browner hue, and
readily distinguishable, since when heated on platinum deflagrates,
emitting sparks and leaving a residuum of very finely-divided oxide of
chromium. The ammonium salt does not, however, so readily crystallise
on account of its considerably greater solubility in water compared
with bichromate of potassium. By comparison, 12 parts of the ammonium
salt are equal to 15 parts of that of potassium. At least 1/3 to 1/4
more of the former may be used without disadvantage or fear of it
crystallising out; it will, on the contrary, improve the quality of
the film or layer. The ammonium salt will also be found comparatively
more soluble in hot water, but care must be exercised that the
solution never reaches the boiling point, neither should the heat of
the drying box ever exceed 50° to 60° C., or the films will present a
pale brown appearance, and will prove alike insensitive and partially
insoluble. The single and tri-salts, offering no advantages over those
already described, may be dismissed without further consideration.
It may be remarked for non-chemists that the addition of any acid
to the chromated gelatine solutions inclines to the formation of
trichromates of the alkalis; and, on the contrary, the addition of
free ammonia, or any other free alkali, produces simple chromates.
The addition of ammonia to the chromated solution has been strongly
advocated in many quarters, but as the result of numerous experiments,
it may be definitely stated that the supposed advantages are more than
counter-balanced by the numerous disadvantages arising from such
addition. The mixing, in equal or other proportions, of the potassium
and ammonium salts has been recommended, but there is no real gain
or sufficient reason for preferring any of these combinations to the
ammonium salt alone. Besides the chromates of the alkalis, several
other salts as well as acids are used in Collotype printing, although
seldom, and then only in small quantities and for special purposes,
such, for instance, as hardening the print layer, or for the purpose
of facilitating the retention of moisture in the film. For the former
purpose small quantities of chrome alum are sometimes added; while for
the latter chloride of sodium or chloride of calcium are sometimes
added to the chromated gelatine solution at the time of coating the
plates, or are added as ingredients to the so-called etching or damping
solution which is frequently applied to the plates during the printing.
Glycerine answers for this purpose, and is to be preferred. It should
be borne in mind that all additions to the film to facilitate its
retention of moisture lessen its adhesiveness to its support. And with
regard to the direct addition of the substances mentioned to the film
during the preparation of the plates, it is not very apparent how such
readily-soluble matters can remain in the film after the prolonged and
careful washing the plates should be subjected to after exposure in the
printing frame. On these grounds the addition of such substances to
the damping solution is more rational and certainly more effective.

=Alum= and =Chrome-Alum= causes the gelatine to set sooner without
precipitation, and harden the layer considerably after drying, and
although gelatine, as well as glue, always contains more or less
chondrin, which is precipitated by alum, great care is necessary in
the addition of the latter; and it is better that such addition should
be made immediately before the hot solution be poured upon the plates,
otherwise a precipitation will ensue, which, although very finely
divided and at first scarcely visible, will become more apparent
during the drying of the plates, and finally show in the picture in
innumerable white spots.

=Silicate of Soda= is almost indispensable as a substratum in the
preparation of collotype plates, although many practical workers still
adhere to the method originally proposed and practised by J. Albert, of
Munich, who used as a substratum a chromated solution of gelatine and
albumen, rendered either partially or wholly insoluble by exposure to
light. The silicate is here considered as having about the consistency
of syrup. If more fluid the adhesive power of the substratum will not
realise expectations, and the plates will require very careful handling
if even a few hundred impressions are required.

The composition of the film, the exposure of the plate through the
back, and the careful treatment of the layer in the actual printing
operations are all matters which considerably affect the “life” of the
plate, and to which we shall again return.

=Chloride of Zinc= is used for hardening special parts of the collotype
plate, and is easily prepared by dissolving—to saturation—sheet zinc in
hydrochloric acid, filtering, and reducing as circumstances may demand.

=Tannin= and =Tannic Acid= in strong solution harden the film, and
may be applied to certain parts to cause it to “take” the ink. For
instance, to remove, or rather harden, spots which refuse the ink and
consequently show upon a dark ground; and also to write names or titles
to the plates. Written additions of this character must, of course, be
reversed, as in lithography. The addition of tannin to the chromated
gelatine before coating the plate is recommended by Waterhouse, he
considering such addition confers greater lasting power to the films so
treated.

=Cyanide of Potassium and Ammonia.=—All alkalis or carbonates of the
alkalis have a directly opposite effect upon the printed layer to
that last referred to. By the judicious use of one or the other of
these agents spots printing light or dark may be either removed or
considerably modified.

=Glycerine and Sugar= and similar easily soluble organic substances,
added to the chromated gelatine, would assist the easier and evener
damping of the plate, but render it more susceptible to damage, and
the desired effect is better attained by suitable additions to the
damping water.

=Organic Acids.=—Citric acid and tartaric acid are recommended as
additions to the chromated gelatine, partially as influencing the
so-called “grain,” and also as additions to the damping solution to
facilitate the production of cleaner prints. Experience with these
substances shows that the print layer suffers from their use, and for
clearing up a plate inclined to yield dirty impressions a weak solution
of ammonia is far preferable.

=Nitric Acid= has even been recommended for occasionally damping the
plate in certain cases, after which the most delicate half-tones should
be reproducible. An experienced collotypist ought never to be under the
necessity of adopting such desperate remedies, which more often than
not rapidly and entirely spoil the plate, and it is better to at once
prepare a new one.

=Ox Gall= remains to be mentioned as exercising a beneficial influence
upon the print layer under certain circumstances. It considerably
hardens the gelatine, and tends to reduce the annoying tendency of
the film to adhere to the paper in the high lights. Ox gall was first
used at the Royal Printing Works in the “glass” printing process there
utilised for the reproduction of line subjects. Some operators of
eminence consider that in collotype its use should be strictly confined
to lineal representations, as by its continued use the half-tones are
partially lost.


INK AND PAPER.

Of great importance is the careful selection of the materials for the
printing proper—_i.e._, the printing inks and papers, and the sometimes
necessary admixtures of the former.

=Printing Ink.=—The most simple and suitable of all greasy or oily
printing ink is the best chalk ink, as used in lithography. It is
composed of finest lamp black thoroughly incorporated with boiled
linseed oil (varnish). The collotypist must, in addition to different
coloured ink for mixing with the black, be provided with thin boiled
oil (middle varnish), and also turpentine and olive oil, the latter
being used to thin or reduce the printing inks, which, as usually
supplied to the trade, are too stiff for immediate use. When in
printing it is necessary or intended to use an admixture of several
colours, they must be first well ground in turpentine and the latter
allowed to evaporate. A small addition to the chalk ink of indigo or
Prussian blue greatly improves its colour and printing power, but may
be considered more suitable for the reproduction of line or stipple
subjects. A dash of Venetian red or carmine imparts to the chalk ink
a warmer tone, resembling the colour of an ordinary silver print.
Whoever ventures on colour printing must be able to prepare all the
necessary combinations with the greatest exactness, and should use for
each a special inking slab and roller. In the chapter dealing with
the printing, further particulars will be given as to the mixing and
thinning of the colours.

=The Quality of Paper= suitable for collotype may be next considered.
Without doubt the best is that known as dull enamel, or chalk paper,
which is now supplied of a pink tone as well as of the ordinary white
quality. It should not be glossy or adhere too strongly to the printing
surface, as the enamel will, under such circumstances, be partially or
wholly torn from the paper, a difficulty equally observable whether
the paper be used damp or dry. As previously observed, the adhesive
power of the printing surface increases with the softness of the same.
This may arise from using a small percentage of bichromate or a short
exposure to light, in which cases it is always more apparent in such
parts, as the densest portion of the negative may have been entirely
protected during the copying in the printing frame, or it may arise
from the addition of too great a proportion of isinglass. On the other
hand, a gelatine film strongly chromated, proportionately longer
exposed, and in which there is no isinglass, will be less likely to
exhibit this annoying tendency.

Well-sized fine glazed papers generally adhere least, and are usually
laid on dry. When the impressions are to be issued without glaze very
thin fine-surfaced cardboard—not enamelled—is frequently used, and
the margin of the printing plate covered with a suitable mask. Any
well-sized paper possessing a fine surface may be used. Impressions on
such paper may be passed through a weak solution of gelatine, and after
drying, rolled, varnished, mounted and again rolled. Any retouching
must be done immediately after the sizing, and before the application
of the varnish. Enamelled papers require a special glaze, not a
lacquer, or are finished without glaze at all.




CHAPTER VI.

PREPARATION OF THE COLLOTYPE PLATE.


The well-polished glass plate must be thoroughly cleaned with alcohol
and ammonia, and it should be ascertained that the surface is entirely
free from scratches. It is then coated with the substratum, consisting
of a dilute solution of silicate of soda and albumen. The following
formula is in constant use by many practical workers of experience, and
answers every requirement:—

  Distilled water                         8 parts.
  White of egg—whisked                    7   ”
  Silicate of soda (of the consistency
    of syrup)                             3   ”

This mixture should be well beaten to a froth or put in a bottle with
pieces of broken glass, well shaken, and placed aside to settle for
half-a-day. Then filter through paper, which should be replaced so soon
as the pores become choked. To facilitate the operation the filter
paper should before use be moistened with distilled water. The surface
of the plate should be flooded with water, and coated as evenly as
possible with the above solution, a small glass rod being made use
of to assist the flow. Air bubbles must be removed, and by quickly
tilting the plate the superfluous solution run off; this should not be
used to coat other plates without being again carefully filtered. If
the substratum be thin, it is not necessary to wash the plate after
drying, but after standing aside two days to harden, with dusting and
warming, they may be coated with the chromated solution of gelatine.
If small crystal formations appear on the surface the plate should be
well washed and again dried before proceeding further. The following
formula for substratum is due to M. Thiel, senior; it contains less
silicate, and the washing before applying the sensitive coating is
never necessary:—

  Distilled water     36 parts.
  White of egg        20   ”
  Silicate of soda     6·2 ”

=Stale Beer.=—Albumen is sometimes replaced by beer, from which by
frequent outpourings the carbonic acid has been removed, and to which
caustic potash has been added until it fails to show an acid reaction
when tested with blue litmus paper (about three to five grammes of
caustic potash to the litre of beer will be necessary). To a litre
of beer so prepared is added 1/3 kilo. of silicate of soda. The
main points in this and also the following operations are careful
filtration, even coating and drying in a clean place entirely free from
dust. Plates previously used or somewhat scratched must before further
use be thoroughly cleaned and the face reground with the finest emery
powder.

=The Sensitising Solution.=—This is manifestly the most important
matter in the Collotype process, for on it depends not only the
durability of the printing plate, but also the method of procedure
in the subsequent operations. It may be here intimated that plates
prepared by the very best formula cannot be expected to yield good
impressions if the whole of the manipulations are not carried out with
the greatest care, and it should be noted

1. That neither too much nor too little of the chromated gelatine
should be allowed to remain upon the plate. It is impossible to lay
down a hard and fast rule, and the exact amount must be determined by
the experience of the operator. Of equal importance, and naturally
connected with this operation, is

2. The even distribution of the solution, the flow of which may be
assisted or directed by the aid of a small glass rod, and by allowing
it to run off more or less at each of the four corners of the plate.
Considerable experience has demonstrated that the coating is applied
most easily and in the evenest manner by resting the plate—previously
warmed to about 45° C.—as horizontally as possible on the cork of a
heavy bottle, the latter standing in the centre of an earthenware dish.
A sufficient quantity of the solution, carefully filtered, and heated
to 45° to 50° C., is then poured on to the centre of the plate and
rapidly spread over it with a glass rod, previously well warmed. So
soon as the surface of the plate has been entirely covered a further
supply of the hot gelatine solution is quickly poured on and partially
run off at each corner. A scarcely perceptible inclination should be
given to the plate, otherwise the layer will be too thin; it ought to
be about the thickness of four or five sheets of Rive paper of 8 kilo.
per ream. It should be borne in mind that the addition of isinglass
will necessitate a comparatively thinner layer than when gelatine is
used alone.

To obviate the gelatine coating becoming uneven great care must be
exercised in removing the plates—when coated—to the drying-box, the
levelling screws of which have been adjusted with great accuracy. The
box should be heated to a temperature not exceeding 50° C.

To satisfy the adherents of isinglass, two eminently satisfactory
formulæ are here given—

         WITH GELATINE ONLY.
  Collotype gelatine      6 grams.
  Water                 700 ccm.

The gelatine is first soaked in the water for one hour, and then
complete solution effected at a moderate temperature, and the solution
filtered through best filter paper. Boiling heat is never required.
Japanese filter paper is the very best. Heat will be necessary during
the operation, which may be conducted either in the drying box or a
warm oven. When filtered, add, with constant stirring, 8 ccm. of a
solution of bichromate of ammonium in water (1 in 8, so that 8 ccm.
solution contains 1 gramme of the ammonium salt), which should also be
thoroughly filtered before addition to the gelatine.

The combined solutions being well incorporated, clear and free from
air bubbles, should, as previously described, be heated to 40° or 50°
C., poured upon the warmed plate, and at once conveyed to the drying
box, the temperature of which has been slightly raised. The box should
be closed, and gradually increased to 50° C., at which heat it should
be steadily maintained until the drying is complete, which usually
occupies one to one and a-half hours, varying somewhat according to
the thickness of the coating and the strength of air current, which is
necessary to the proper and rapid drying of the films. It may, under
some circumstances, be necessary to augment the admission of air; this
may be done by slightly raising the lid of the drying box. The current
must freely circulate in all parts of the box, and remain as constant
as possible. If subjected to sudden fluctuations in the air current or
temperature, the plates will dry unevenly, and endless troubles ensue.

=The Grain.=—The so-called grain which is necessary for the printing
first shows itself on the completion of the washing of the plates
after printing in the copying frame. It is a peculiar, net-like
formation, varying in fineness, and similar in character to the
unwelcome appearance known to carbon printers as reticulation. It
arises in consequence of the uneven distribution of the soluble layer
in comparison to the substratum. In Collotype, its production is
promoted by thicker layers and slower drying at a temperature of 45°
to 50° C. The addition of isinglass also seems to aid the production
of grain. Certain varieties of gelatine which possess great power of
absorption give a smaller grain. Creutz’s gelatine may be mentioned as
an example of this class. An addition in small quantities of dilute
acid, particularly those of organic origin, as acetic or tartaric, tend
likewise to the production of grain. Insoluble powders, as of glass
or flint stone, may be added, but only in the very finest state of
division, and in very small quantities.


FORMULA WITH ISINGLASS.

Two grammes of the best Russian isinglass are cut up into the smallest
possible pieces with a pair of sharp scissors, soaked in 25 cc. of
water for 12 hours, heated nearly to boiling point until solution is
effected, and then filtered while hot through close flannel. Cover six
grammes of good Collotype gelatine with 50 ccm. of water and allow to
stand, heat nearly to boiling point and thoroughly incorporate the two
solutions, again, while hot, filter through paper or close flannel.
To this is added 11 cc. of the filtered solution (1·8) of bichromate
of ammonium, as previously referred to. The complete solution is then
heated to 50° C., or should it exceed that temperature it is allowed
to cool to it, and the plates warmed, coated, and dried in the manner
previously described. It is not advisable to overcrowd the drying-box
by attempting to dry too many plates at the same time: it necessitates
a too frequent examination of the contents and so interferes with the
evenness of the drying, and as this is a point of even vital importance
no risk should be incurred.

The plates being properly dried allow them to remain in the box
for some time longer, the source of heat being either removed or
extinguished, and the whole allowed to cool gradually. If the plates
are removed too quickly in their fully-heated condition—particularly
when thickly coated—the too rapid contraction of the glass will crack
and destroy the film; by gradual cooling such accidents are avoided.
When finished the plates may be kept in a cool, dry place for two or
three days. Many operators keep them this length of time purposely,
believing they thereby obtain finer results. The plates so kept must,
of course, be thoroughly shielded from actinic light.

=Negatives=, with regard to their suitability for Collotype, may here
be considered, as the after result naturally depends considerably on
their adaptability to the process. They should be quite free from
fog or yellow stain, and for half-tone subjects not too intense.
The greatest difficulties will present themselves in the production
of portraits or such work from nature by the Collotype process.
Photographer and printer ought, so to speak, to work hand-in-hand.
The negative must show the finest gradation from clear glass in the
shadows to the necessary density in the high lights, quite free from
veil or fog, and intensified very little, if at all. They should be
produced in a studio where the light is thoroughly under control. If
not to be stripped all negatives should be taken on patent plate and
protected by a coat of varnish, sufficiently thin to offer no obstacle
to the production of sharp prints, and yet sufficient to obviate in a
great measure the risk of damage by the pressure it is subjected to
in the pressure frame in contact with the unyielding surface of the
Collotype plate. The risk of breakage at this stage always renders
stripped films preferable, their elasticity better enabling them to
withstand the pressure. The gelatine layer applied to the negative
before stripping must be as thin and even as possible, as from thick or
uneven films it is almost impossible to produce a sharp print. If the
negative is of a line subject, and it is desirable to have clear whites
that the impressions may resemble as much as possible the original,
the lines in the negative must be clear, but the remaining portions of
great density. The ink for such work should consist only of pure chalk
printing ink, which will be generally found to give stronger contrasts
than the usual mixed Collotype inks.

=Retouching Negatives and Plates.=—The negatives must have all defects
made good by the retoucher, all blemishes being moderated as far as
possible. Retouching on the Collotype plate or print should not be
required; but this is seldom so, as during the printing the negatives
frequently sustain slight damages. Retouching the printing surface
is seldom very successful. The alteration easiest effected is the
removal of small light spots which refuse to take the ink, and such may
be removed by touching with a fine brush dipped in a strong aqueous
solution of tannin, this alteration being made upon the finished
plate after it has been washed and dried. With this tannin solution
inscriptions may be inserted which have to appear black in the print.
Or a solution of gum arabic, to which has been added a solution of
bichromate of potassium, may be used, and after such addition the
plate is once again exposed to light. Writing which has received too
much exposure, and which should appear in the finished print black on
a white or light ground, often appears white. This defect arises from
the gelatine on which the light has had little or no action swelling
to such an extent that the letters are buried or sunk into the plate
too deep to be touched by the roller when the plate is inked. It may be
rectified by further thinning the ink with varnish. The removal of dark
spots from the print layer can never be completely effected. Ammonia,
cyanide of potassium, oxalic and other acids have from time to time
been recommended, but this treatment will prove effective for only a
few impressions.

Negatives should therefore be very carefully and systematically
retouched and carefully preserved from damage during the printing.
Another method of applying writing, such as the names of firms, &c., is
to get them printed from small type on thin gelatine films and attach
them to a clear or erased portion of the negative during the printing
in the pressure frame. Writing so added will appear as white letters
on a black ground. It will often be found practicable to attach the
written or printed matter to the original while photographing, and so
include it in the negative at one operation.

=Printing under the Negative.=—The printing of half-tone plates is best
performed in diffused light; to hit the exact exposure is as important
as it is difficult, and depends not only on the actinic power of the
prevailing light, but also on the quality of the negative and the
sensitiveness of the layer. The greater the amount of bichromate the
latter contains, the greater its sensitiveness, and consequently the
exposure is shorter than for one containing less of the sensitising
salt. A thinner layer must not be printed so long as a thicker one,
or dark prints, lacking in contrast, will result. On the other hand,
a thicker layer may be submitted to a comparatively longer exposure
without harm; the exact time must not be greatly exceeded or it will
happen that the blackest portions, written titles for instance, will
not take the ink. During printing, one may with advantage shade such
portions a little. The examination of the back of the Collotype plate
is the safest method of judging the correct exposure during the
copying, but every precaution must be observed during such examinations
that neither the plate nor negative be moved from their original
position. Only when the negative is very clear may the picture be seen
by reflected light as a positive; it will in such cases appear on a
dark ground. It will be found difficult, particularly for a beginner,
when making an examination in the copying frame, to distinguish between
the dark original picture and the pale brown image of the Collotype
plate, as they naturally completely cover each other. By the dark brown
tone of the uncovered margin of the print layer a certain indication is
afforded of the completion of the copying.

=An Actinometer= may be used as an exposure gauge, as in carbon
printing, and as a slight indication of the necessary exposure. When
using the small cube[H] photometer with chloride of silver paper,
five to seven tints may be printed, but the different modifying
circumstances previously referred to must all be duly considered. Under
a clouded sky in winter, using a dense negative, it may take a whole
day to complete the copying, while in clear direct sunlight, perhaps,
from the same negative, a quarter of an hour would suffice.

  [H] The scale actinometer is one requiring less attention.—TRANS.

=Masking= should be resorted to to form a margin at least an inch wide
round the four sides of the negative, either by painting round the
same with Indian ink, or by attaching to the negative strips of opaque
paper, or, better still, thin tinfoil.

=Sunning.=—When sufficiently exposed, _i.e._, when the brown picture
with all its half-tones and details is complete, the plate is removed
from the copying frame and placed, face downwards, upon a piece of
black velvet, and exposed for a short time—five to ten minutes—to a
good but not direct sunlight, so that it may pass through the glass
plate and harden the back of the print layer. A sheet of ground
glass may be placed over the plate to thoroughly diffuse the light,
and prevent any scratches or damages to the back of the glass plate
producing any detrimental effect upon the printing surface.

=Washing the Plate= is the next operation. The plate is removed into
the dark room and placed in clean cold water, which should be often
changed—every half-hour—unless an automatic washing apparatus[I]
is used; this is continued until the plate no longer has a yellow
appearance, and the picture is visible only as a slight brown image.

  [I] Jefferies’s Patent “Perfect” Washer is a very suitable
      appliance, and may be used for Collotype plates, negatives,
      or paper prints.—TRANS.

=Hardening the Film= is effected by soaking it for a quarter of an hour
in a one per cent. solution of alum. The plate is again washed, and the
surface evenly dried with fine tissue paper, and placed aside for at
least two days that it may thoroughly dry.

=An Alcohol Bath= is used by many operators to immerse the plate in for
half an hour after drying it with paper, perhaps with the intention
of drying the film quicker, or to strengthen the layer and assist the
formation of the grain, but there is no gain by this procedure, and, as
the bath is an expense, it may be omitted.

=The Damping Solution=, or so-called etching fluid, is of much greater
importance, and it is necessary that the plate be submitted to it
before printing be attempted.

=Tinted Grounds= often enhance the appearance of prints, and may be
imparted to them by the addition of an aqueous solution of red, yellow,
or other suitable colour, to the damping solution, which is applied in
the ordinary manner. The plate is superficially dried, inked up, and
printed from in the usual way.




CHAPTER VII.

NEGATIVES SUITABLE FOR COLLOTYPE.


A Collotype plate may be readily produced from any negative, but the
highest results are naturally only obtained when the negative is
prepared with a view to its special use. First should be considered the
question—May the negative, without detriment to the finished print,
be utilised without a reversal? In the not very frequent case of this
important point being immaterial, it is simply necessary to produce
the negative on patent plate, and it is at once available for printing
from. As the negative may easily sustain damage in any of the various
operations, it should be thinly and evenly varnished; this, while
affording protection, does not mar the sharpness of the resulting print
to any appreciable extent.

=Reversed Negatives.=—In the majority of cases, the resulting copy has
to exactly correspond with the original as regards the position left
and right, and in such cases the negatives will have to be reversed.
This is usually effected in one of four different ways—

  1. Reversal of the image by reflection with a prism or mirror, or
     reversing the plate.

  2. Stripping the negative from the glass.

  3. By the dusting on or powder process.

  4. By the use of negative films.

The second is that usually adopted. With regard to the special features
desirable in negatives for Collotype, one giving a good silver print
will answer equally well for Collotype—they should incline rather to
softness than the other extreme. It has been remarked that they should
be as free from veil or fog as possible, and may be intensified or not
according to the judgment of the operator.

=Portraits from Nature=, with their fine half-tone, and at the same
time necessary contrast of light and shade, are the most difficult to
reproduce in Collotype. The negatives should be perfect in gradation,
and such as are usually only obtainable from a talented operator who
has the lighting of his studio entirely under his control.

=Black and White= subjects, on the contrary, for their satisfactory
reproduction, require a negative of the utmost density, but perfectly
clear in the lines. Such are better produced by the collodion process,
as directed for photo-lithography. For subjects in lines or dots
entirely free from half-tone, photo-lithography is more suitable for
reproduction than Collotype, where price is a consideration.

=Reversal by Reflection=, by means of a mirror or prism, necessitates
a special and rather expensive apparatus, and the exposure being
somewhat lengthened, it is, although quite successful, more suitable
for lifeless objects.

=Stripping the Collodion Film= is a safe and cheap procedure for
producing the necessary reversal, and in the subsequent printing
operations the danger of breakage, when compared with glass, is
reduced to a minimum. The glass plate, free from defects, must be well
cleaned, and it is safer, and renders the stripping more certain, if
it be covered with a fine film of pure beeswax. This is best applied
by rubbing over the surface a few drops of a solution of beeswax in
benzole and carefully polishing, at the same time avoiding the entire
removal of the wax. The piece of linen used in the operation should be
rubbed upon a lump of wax previous to the polishing. The plate must on
no account be gelatinised or albumenised, except round the edge only,
as a precaution against premature slipping.[J] Use a tough collodion,
and otherwise proceed as usual for the wet process. After the negative
is finally washed and dried it should be varnished with a thin solution
of gum arabic, to which has been added a few drops of a solution of
chrome alum. After complete drying the margin or edges of the plate
are rubbed with a little tallow. To prevent overflow the plate is
accurately levelled and flooded with a solution of 10 parts gelatine
soaked in 60 parts of water and dissolved by heat, to which is added
20 parts of alcohol and 6 parts of glycerine, using 1 dram of the
solution to each four square inches. A few drops of phenyl, carbolic
or salicylic acid may be added to the solution as a preservative, and
the whole before use well filtered, while hot, through linen. The
hotter the solution during the pouring on the more evenly the coating
will run upon the glass, and it may be assisted in its flow by careful
tilting of the plate. The use of paper strips is dangerous, and,
notwithstanding the gum, extremely liable to damage the negative.

  [J] Instead of wax the plate may be dusted over with powdered
      French chalk, all traces of which are removed before applying
      the collodion. After such treatment the film is scarcely
      likely to leave the plate before required. But as a further
      precaution, if the edges of two plates be drawn across each
      other a rough edge will be produced, to which the collodion
      coating will adhere tenaciously.—TRANS.

=Reversal of the Plate=, either collodion or gelatine, is another
method of securing reversed negatives, and consists simply in inserting
the sensitised plate in the dark slide with the uncoated side towards
the interior of the camera. A modification of the dark slide may be
necessary, and it will be obvious that the ground glass focussing
screen must be reversed, or the focus corrected after the insertion
of the dark slide by shortening the camera a distance equal to the
thickness of the sensitive plate. Dry plates present great advantages
in this method, but, in development, density must be judged entirely by
transmitted light, as the image is formed in, not upon, the film. As
the rays of light pass through the glass to the sensitive surface, it
is necessary that the uncoated surface be quite clean, and the glass
itself should be perfectly free from bubbles, scratches, or other marks.

The plate should remain in its levelled position for about fifteen
minutes to set and then be carefully removed to a safe and airy
position, gelatine side outwards, and allowed to dry. This operation
will probably take two days; the hot gelatine layer should be about 3
mm. thick. The negative may then be coated with a toughened collodion
(one or two per cent. of castor oil added to plain collodion). The
plate is placed aside, and in an hour will probably be dry and ready
for the next and final operation. Cut with a knife through the film,
take it by one corner, and, without pause or hesitation, strip it from
the glass.

Any necessary retouching should be done upon the gelatine surface after
roughing it sufficiently with pumice powder to enable it to take the
pencil, and all such work must be completed before removing the film,
particularly if it has been damaged, as in such places the colour used
in retouching would cause an adherence, and the film would almost
assuredly tear in stripping.

Upon the quantity of gelatine solution used the nature of the film
depends. It should be entirely free from air bubbles. Too thick a
layer almost always cockles, and does not lie flat during printing,
in consequence of which portions of the picture will not be sharp in
the print. On the other hand, too thin a layer is extremely awkward
to handle in the larger sizes, and it is preferable to transfer it in
a reversed position to a sheet of plate glass coated with indiarubber
solution.

=Gelatine Plates for Stripping= are in the market. In their
preparation it is necessary to first coat the glass with a solution of
yellow wax in benzole, or an indiarubber solution, before coating with
emulsion, such plates being known as strippers in America and Germany.
When finished, the negative is placed, together with a gelatine film—or
“skin”—in a solution of glycerine and water, both are withdrawn
together, a squeegee applied to remove the superfluous solution, and
the negative, with its adhering skin, placed aside to dry. Afterwards
the edges of the film are cut through, and the negative removed from
the glass.


STRIPPING THE FILM OFF GELATINE NEGATIVES FOR COLLOTYPE.

In the _Photographisches Archiv_, Mr. Wilh. Otto, a well-known German
Collotype printer, describes the following process:—

“The glass plates are first cleaned by being well rubbed with a
solution of caustic potash, after which they are thoroughly rinsed and
polished with tripoli. The next proceeding is to wax them by rubbing
one face over with a solution of 12 grains of beeswax to one ounce of
ether, this being applied by means of a piece of cotton or linen cloth
saturated with the solution. In polishing off the excess of waxing
solution, care must be taken not to destroy the continuity of the
extremely thin and almost invisible film of wax which it is necessary
to leave on the glass to ensure the easy and complete separation of
the film. Some operators prefer to wax the plates by warming them to
a temperature somewhat over the melting point of wax, then rubbing one
face over with a lump of the article, the excess being now polished off
with a piece of flannel before the temperature of the glass falls below
the melting point of the wax. It may be mentioned that, before waxing,
it is as well to mark the working surface of each plate by making a
diamond scratch in one corner.

“A small piece of cloth, moistened with ether or benzole, is now used
to remove all traces of wax from the edges of the plates, a margin of
the width of an inch being sufficient; and it is well to paint this
margin with albumen and to allow it to dry. Unless the edges of the
plate are entirely free from all traces of wax, there will be a great
probability of the film separating from the glasses at too early a
stage, and adhesion at the edges is made more certain by the use of
albumen. A moderately diluted solution of silicate of soda may be used
instead of albumen.

“The waxed side of each glass is now coated with collodion containing a
little castor oil; eight grains of tough pyroxyline and three drops of
castor oil to each ounce of mixed solvents (equal volume of alcohol and
ether) being a convenient preparation.

“The collodion being dry, the plates are coated with emulsion. The
emulsion flows very badly on the collodionised surface, but by using a
bow made of a piece of sewing cotton stretched across an arc of thin
iron wire the difficulty may be readily overcome. The thread is to
be drawn over the surface of the plate after the required quantity of
emulsion has been poured on, and it is scarcely necessary to say that
the glass should be supported on a levelling stand.

“Plates prepared in this way are developed and fixed in the ordinary
manner, and when a plate is dry it is sufficient to cut through the
film inside the edge which has been cleaned of wax, when the film
negative can be easily stripped off. In this case, however, the film
is very thin, and it is often desirable to thicken it somewhat before
stripping. For this purpose a piece of thin commercial sheet gelatine
is taken, and soaked in water till it becomes quite flaccid, and this
is laid on the negative, care being taken that no air is enclosed
between them. A sheet of wet paper, or of mackintosh, is now laid on
the gelatine film, and all excess of water expelled from between the
negative and the soft gelatine film by stroking the upper surface of
the paper, or of the mackintosh cloth, with a squeegee—that is to say,
with a strip of indiarubber set in a wooden handle.

“It is now easy to remove the paper or the indiarubber cloth which was
used to protect the soft gelatine from the action of the squeegee,
and the plate can be set up to dry. When dry, the film is cut through
within the border from which the wax was cleared off, and the film will
separate readily; but should there be any tendency towards a too early
separation, owing to the contractile force of the fresh thickness of
gelatine, the edges of the plate may be bound with strips of gummed
paper.” (_Photographic News._)

=Stripping Ordinary Gelatine Plates.=—Any make of dry plate may be
stripped by the following method:—The plate is coated with strong
tough collodion upon the gelatine side; as soon as the collodion has
set, it is plunged into cold water and washed until all greasiness
disappears. In the meantime, a piece of “flexible support,” as used
in carbon printing, is carefully waxed by rubbing upon its surface
a solution of turpentine 140 cc., beeswax 2 gm., resin 6.5 gm. This
should be applied evenly by means of a piece of flannel, the solvent
allowed to evaporate, and the waxed surface polished with a second
piece of flannel. The support should then be placed in cold water
and allowed to become quite flexible, in which state it may be used
at any time. Remove the negative from the clean water, and place in
a bath of methylated spirits 150 cc., glycerine 3 cc., water 30 cc.,
hydrofluoric acid 3 cc. An ebonite, guttapercha, or lead dish should
be used to contain this solution, with which the fingers should come
in contact as little as possible. The film should be watched narrowly,
and when loose upon the glass—but not actually detached—the plate,
still bearing the film, should be placed in a bath of clean water, well
washed, and all surface moisture absorbed by careful blotting. Take
the flexible support from the water in which it has been standing, and
without removing any adherent moisture, carefully lower it upon the
film, which is still resting upon its original glass plate, squeegee
it into contact with the negative film, avoiding air bubbles, place
under a weight, and allow to stand for ten minutes or a quarter of an
hour. The film will then be found to adhere to the flexible support,
and may be readily removed from the glass. It should be allowed to
dry spontaneously upon the support, no attempt being made to remove
the film until it is “bone” dry, when it will readily part with the
temporary support, remain perfectly flat, and may be printed from
either side with perfectly satisfactory results. Should any of the
waxing solution remain on the surface of the film, it may be removed by
the careful application of a little turpentine applied on a small linen
pad. Do not use methylated spirit for this purpose, as it may cause the
film to “buckle.” Any stripped films may be conveniently preserved and
kept flat between the leaves of a book.

=The Powder Process= is one of importance for reproducing and, at the
same time and at one operation, reversing negatives, but for some
reason is far more resorted to upon the Continent than in England,
where few only have been able to thoroughly master it. Failures are
usually attributed to changeability in the climate, but, although
success is by no means uniform, it is a thoroughly workable process.
The basis is a chromated solution of gum arabic, with which a plate is
coated, dried, and in a thoroughly dry condition exposed to the light
under a negative. The greater the extent to which the light acts, the
smaller will be the amount of moisture the coating of the plate will
absorb when exposed to a damp atmosphere. If the surface of the plate
be now dusted over with a fine powder, as drop black, or graphite, the
greater the amount of moisture certain parts of the film have absorbed,
the greater will be the amount of colour such parts will retain, and so
exactly reproduce the light and shade of the original negative. Simple
as this process reads, the difficulties must not be underrated, and
the operator will probably find plenty of opportunity for the exercise
of his patience and ingenuity. A consideration of the process as just
described will show that a plate which has only been subjected to a
short exposure will, on dusting over and development, be found to
exhibit greater density than one that has received a longer exposure,
a careful adjustment of which will give to the operator great control
over the density and characteristics of the reproduced negative, a
power certainly too important to be overlooked. A reliable formula for
the preparation of a gum-chromate solution for this process is due to
Dr. Leisegang:—

  Rain water                     1 litre.
  Dextrin or glucose            50 gr.
  Gum arabic                    50 gr.
  Honey                         10 gr.
  White sugar                   20 gr.
  Glycerine                      5 gr.
  Cold saturate solution of
    bichromate of ammonia      100 gr.

which, after careful filtration, is poured over a well cleaned and
dusted glass plate. After draining a little by standing on blotting
paper, dry over a spirit lamp, and place, while still warm, under
a negative in the printing frame—one minute in the sun, 10 to 20
minutes in the shade, is about the necessary exposure. As previously
mentioned, the shorter the exposure, the denser will be the resulting
negative, a result at variance to any other photographic printing
operation. To develop the picture the glass plate is placed, coated
side upwards, upon a sheet of clean white paper, then, with a soft
camel-hair brush, dust over the picture some very finely-ground
Siberian graphite, working the same backwards and forwards over the
plate until the necessary strength is attained. If the picture should
develop too quickly, and take the colour all over, the cause is under
exposure; should the powder adhere unevenly, or the picture present a
smudgy appearance, the coating must have absorbed too much moisture,
and must be again warmed before further development. This precaution
is particularly necessary during the winter months. If a prolonged
development be necessary, and after continuous dusting a picture
lacking in contrast be the result, it is occasioned by over exposure.
On completion of the development the picture should be finally and
carefully dusted with a soft brush to remove the superfluous powder,
coated with a thin plain collodion, and placed in water, which should
be frequently changed, until it fails to show any trace of yellowness.
The plate should be afterwards retouched and varnished.

=Negative Films= have now been before the public some time, and
have been considerably used as reversed negatives by printing with
the back of the film in contact with the plate. The four principal
varieties are, in the order of their introduction—1st, Eastman’s; 2nd,
Froedman’s; 3rd, Pumphrey’s.

=Eastman’s Stripping Film= consists of a substantial paper coated
with a layer of soluble gelatine, upon which is spread a coating of
insoluble gelatine emulsion; they may be exposed in contact with a
sheet of glass in an ordinary dark slide in the film carriers or on
the roller slide. There are no special precautions necessary in the
development, except that no alum may be used previous to stripping. For
use as reversed negatives the ordinary operations are greatly shortened
and simplified. A sheet of plate glass is coated with collodion,
allowed to set, and then placed in a dish of cold water until all
greasiness has disappeared. After fixing and washing, the negative,
still supported upon the paper, is placed over the collodionised plate
in the same dish, and the two brought out face to face. Upon the back
of the negative paper place a piece of blotting paper, cover it with a
sheet of oiled paper—as used in copying letters—and apply the squeegee;
place a dry sheet of blotting paper upon the back of the film, cover
it with a sheet of glass or other flat surface, upon which place a
weight. In fifteen minutes the plate may be placed in warm water—about
130° F.—and in a short time the paper backing will float off. By gentle
washing with hot water remove the soluble gelatine from the film
resting upon the glass, and place the negative aside to dry. It is then
complete, and reversed.

=Froedman’s Films= consist entirely of gelatine, require no stripping,
and may be printed from either side. The film is somewhat difficult to
handle in the developer, and has to be dried by spirit. One feature
against their employment in Collotype is a yellow stain, which probably
arises from the bichromate with which the film is hardened, and
although more apparent where the negative is protected by the rebate of
the dark slide, it undoubtedly pervades the whole picture.

=Pumphrey’s Lifting Films= are the latest and best of a series of films
introduced by the same maker. They consist of a basis of paper coated
with a waterproof varnish on one side, upon the other being spread an
indiarubber coating possessing considerable adhesive power; to this
is attached the gelatine film proper, which consists of two layers,
one of plain gelatine, and the other the sensitive emulsion. The films
should be exposed in the camera between two glass plates, and the
spring of the dark slide should be of considerable strength to insure
flatness of the film, and consequent sharpness of the image. The films
during development may be treated exactly as an ordinary plate, the
manufacturer recommending Beach’s developer. When in the bath they seem
little liable to damage, and may be handled with great freedom and
facility. Upon completion of the development, fixing, and washing, the
paper backing or support is attached by means of paste to a substantial
and smooth card. As a precaution, not always necessary, but usually
advisable, against the film prematurely separating from its support,
around the edges gummed paper strips may be attached to the card, and
allowed to extend over the edges of the gelatine film to the extent
of 3 mm. When dry the film may be varnished, and afterwards lifted
from its support by first cutting through the gelatine and passing the
blade of the knife round the edges between the film and the temporary
paper backing, the latter remaining attached to the card. The two are
by these means readily separated, and the resulting negative film may
be printed from either side without disadvantage, and is of sufficient
strength to withstand a considerable amount of rough handling.

=Other Methods of Reversal.=—There are processes of copying, usually by
first producing a transparency and from that again a negative. If the
wet process is used throughout, a copying camera is essential in both
stages. Should dry plates, however, be used, the transparency may be
produced in the camera and the negative by contact in a printing frame,
or _vice versa_, or both may be produced by means of the camera. If
the transparency be produced by the carbon process a negative may then
be made from it by contact, and the necessary reversal will be brought
about without the use of the copying camera.




CHAPTER VIII.

PRINTING IN THE PRESS.


The etching or damping and rolling-up of the Collotype plate presents
difficulties which are greater even than those met with in the
preparation of the plate. These remarks also apply with equal force
in photo-lithography, and whoever stops at the preparation of the
plates or the photo-lithographic transfer, and leaves the subsequent
operations to be performed by another, should not be considered either
as a collotypist or photo-lithographer. The whole success depends upon
a succession of apparent trifles; many errors it is impossible, or at
any rate difficult, to rectify, and great care should be taken that
nothing is overlooked, or from some trivial cause the whole may result
in failure.

Firstly, remove all adherent matter from the back of the plate, as
the smallest amount of dried gelatine, particle of grit or other hard
matter will suffice to cause the fracture of the strongest glass plate
on the first application of pressure.

=The Etching or Damping Solution= in most common use consists of a
stock solution of five parts water, one part liquid ammonia, three
parts glycerine, and one-tenth part of nitrate of lime. For use add
five or six parts of this solution to 100 parts of water, sufficient
of this being used to well cover the plate when placed in a clean
dish. Another reliable formula is one litre glycerine, 600 cc. water,
chloride of sodium three grammes. Plates may be immersed in these
solutions for a time extending from ten minutes to five hours, or they
may be well flooded with it, wiped off, and dried with blotting paper.

The press having been examined, oiled, and put in thorough working
order, the next consideration will be

=Fixing the Collotype Plate=, which may be performed in several ways.
Immersing the plate in the etching fluid precludes the old method of
cementing it on with plaster of Paris, or glue and whitening, but it
may be fixed by adhesion to a bed of glass or a polished iron plate, or
a special and somewhat complicated frame may be procured for securing
the thick printing plate by means of adjustable clips secured by
screws. Should the printing surface be upon a thin glass adhesion alone
will be found sufficient, a few drops of water causing the printing
plate to adhere to the thicker glass plate underneath. This method
has the disadvantage that it is most difficult to ensure the position
of the plate being in keeping with the mask on the frame. Should the
mask be placed directly upon the gelatine surface of the plate it will
not last many impressions without either tearing or causing damage
to the surface through the formation of creases or wrinkles. If the
picture has to be trimmed without margin, and mounted—either with or
without varnish—the masking is altogether unnecessary. The preparation
of the ink and rollers should next be proceeded with. Supposing the
work in hand to be one of a simple character—say the reproduction of
an impression from a copperplate in black—take a piece of the best
chalk ink about the size of a hazel nut, in an unthinned condition, as
supplied to the printing trade, and with an iron spatula or palette
knife spread it upon the inking slab. Add one-quarter the amount of
middle varnish (refined and odourless), one drop of olive oil, and one
or two drops of best French turpentine, incorporate thoroughly by means
of the palette knife, divide, and apply one-half to the roller. The
next operation is the important one of

=Distributing the Ink.=—A really good leather roller, the handles of
which should be encased with easy fitting leather covers, is most
suitable for the purpose. The ink, by careful manipulation of the
roller, should be gradually distributed over the entire surface of both
roller and slab in a perfectly even and regular manner. Should any
small lumps be observable upon either surface they should be carefully
removed with the palette knife and the rolling and distributing again
proceeded with, as on careful attention to this matter the excellence
of the resulting print greatly depends. The printing plate being well
secured, its moistened surface should be very evenly dried. This is
best effected by means of a roller covered either with fine cloth or
washleather, or a fine soft linen cloth may be used as a substitute.

=Rolling up.=—Apply the inking roller with light pressure to the
nearest edge of the plate, and roll backwards and forwards over its
surface several times; an experienced printer will at once perceive the
condition of the surface. For the first inking a stiffish ink should be
used, as the plate will not then so readily become dirty. By repeated
rolling in different directions, and what is of equal importance,
with varying pressure, endeavour to distribute the ink with perfect
evenness, and with a view of producing a clear and vigorous inking,
which will yield a similar perfect impression. It should be remembered
that

1. A slow rolling with heavy pressure deposits ink on the plate; and

2. Light and quick rolling removes the ink from the print layer.

By modifying the treatment of the plate, and varying the application
of the roller and damping solution, an experienced printer will
demonstrate his power of producing from the same plate flat, weak, and
unsatisfactory impressions, or prints as clear and vigorous as may
be desired. The first application of the ink having been made with a
leather roller, it should be distributed, and the half-tones improved
by the application of a smooth roller, preferably of glue composition.
Without this second inking, it will be found impossible to produce the
highest results in half-tone.

=The Second, or Composition Roller=, must be lightly charged with ink
considerably thinner than that applied in the first instance, the
remarks concerning the pressure applied to the leather roller applying
with equal force in this case. By light, quick rolling, the ink is
partially removed from the plate, while heavier pressure and slower
movement will deposit ink and strengthen the shadows.

When the inking is complete, the frame with the mask is placed in
position. The printing paper, which may be either strong, well-sized
letter-paper, thin cardboard, or the paper known in the trade as “dull
enamel,” cut to a suitable size, is adjusted over the mask, and backed
with a couple of thicknesses of smooth paper. This again is covered,
with the tympan attached to its frame. Push the bed of the press so far
under the scraper that the latter, when pressure is applied, will nip
the plate about one centimetre from the commencement of the picture.
This position has to be ascertained by trial before covering with the
second or tympan frame.

=The Scraper= being regulated so that it will give a sufficient
pressure, pass the bed quickly through the press to the extent
necessary to produce a complete impression. The length of traverse
of the bed during printing can on most presses be regulated by side
screws, or the tympan may be lightly marked. After releasing the
pressure, the bed is withdrawn, the tympan and masking frames thrown
back, and the printing paper cautiously raised by one corner. It often
adheres slightly to the printing surface, and this is usually an
indication of a good plate. The adhesion may, however, at times be so
strong as to tear the paper, or, in the case of enamel paper, remove
the chalk coating. As previously mentioned, the scraper should be
selected of a width somewhat exceeding that of the picture, but never
exceeding that of the glass plate. It may be left plain and moderately
sharp, or covered with leather.

=Damping the Plate= between each impression will usually be
unnecessary, providing a good sample of gelatine is used, and the
damping solution contain a sufficient quantity of glycerine. In cases
where the Collotype plate has been over exposed, or the subject be one
which requires an absolutely white background, damping between each
impression will be absolutely essential. Where it is omitted for any
length of time, the whites of the pictures will always be more or less
degraded or tinted. Should the early impressions not be satisfactory,
patience should be exercised, and by careful treatment with the
roller or rollers, and care in the damping, favourable results will
often ensue after the first few impressions have been pulled. Only
from actual damage to the print layer, or excessive over exposure in
the copying frame, need the plate be placed aside as in a hopeless
condition. The beginner should guard particularly against mechanical
damages in damping; drying and rolling. Lithographers are inclined to
treat the delicate printing surface with the same vigour and energy
that they would apply to the more substantial lithographic stone to
which they are accustomed.

The following directions from “Kleffel’s Manual of Photography” are
to be recommended in printing line subjects, particularly in “glass”
printing direct from the negative:—“The chromated layer of gelatine
must have been submitted to a sufficiently long exposure to ensure it
taking the ink over the whole surface. For the first rolling in of the
plate, the ink should be composed as follows: White wax, 45 parts;
middle varnish, 5 parts; gum elemi, 15 parts; litho ink (about 5s. per
lb.), 20 parts.

“After the plate has been thoroughly rolled in and blackened, it must
be rubbed with a piece of unbleached muslin, previously saturated with
the following solution: 30 parts of ammonia and oxgall (about equal
parts), 30 parts gum arabic, 90 parts water, until the picture develops
perfectly clear. Dry with a clean piece of muslin, and roll in for the
printing proper with ordinary thin copper plate printing ink. Plate
paper, similar to that used in printing from the copper plate, is most
suitable.”

When printing operations are complete, the rollers, printing plates,
and inking slabs should be at once cleaned, as the varnish colours soon
harden and create difficulties.

=Cleaning Leather Rollers= without damaging them requires considerable
practice. They are always scraped with a clean knife, and the
operation should be performed in one direction, to ensure which it
is advisable to mark one of the roller handles. Leather rollers not
in constant use, before being put aside, should have their surfaces
carefully and thoroughly rubbed over with tallow, which must, of
course, be scraped off before the roller is again used.

=Cleaning Composition and Indiarubber Rollers= should not be effected
by means of scraping, but their surfaces should be cleaned with
turpentine, applied with a linen rag free from lint.

=Cleaning the Plates.=—Turpentine is used to free the surface from
every particle of ink, and after the thorough evaporation of the
spirit, the plates should be well washed in water to remove all trace
of the damping solution, dried, and stored in a cool place. It is
sometimes a matter of difficulty to remove ink from Collotype plates
that have been printed from, but a simple method is to pour over the
plate—as in developing a collodion picture—some lukewarm water. This
will dissolve a thin layer of gelatine, and enable one to at once
proceed with the work.




CHAPTER IX.

FINISHING AND VARNISHING COLLOTYPE PRINTS.


=Retouching Prints.=—Under the above heading Leon Vidal, in his work
“Traité Pratique le Phototypie,” gives the following directions, which
I reproduce from the “Photographic Archives.” Even with the utmost
possible care in the preparation of the printing surfaces there will
be required in most impressions a little retouching, if only to hide a
few white spots. In large orders this cannot be carried to the extent
it is in silver prints. It happens in printing that particles of dust
find their way to the plate, and cause either light or dark spots in
the impressions; the former are covered by touching with ink, the
latter are removed with the erasing knife, and the white spot resulting
from the operation is toned down with ink. This spotting is quickly
performed. The paper being dull a colour should be used containing only
a small proportion of gum; it will then be invisible. Prints which
it is intended to varnish should not be spotted until they have been
sized, unless printed upon a paper already impervious to the varnish.
The colour most suitable of all is the actual printing ink thinned
with turpentine, by using which the trouble is avoided of mixing any
special colour to match the tone of the impression, as the two colours
are necessarily identical. Another advantage gained by adopting this
method is that the spotting may be completed before sizing, as the
aqueous solution of gelatine will not cause it to run. For impressions
in pure black the lithographic chalk is probably the best medium for
correcting proofs, as the colouring matter will be found to well
harmonise with the general appearance of the picture. A blacklead
pencil, on the other hand, is quite unsuited for the purpose on account
of the highly metallic appearance visible wherever the pencil has been
applied to the print. Retouching or spotting should not extend beyond
the removal of light and dark spots; the correction of larger faults
should not be entertained, but a fresh printing surface produced.
Faults present in the original negative should be carefully retouched
and removed or reduced as far as possible. Should the white margins of
the picture become soiled by contact with the inky mask or by finger
marks, they may be cleaned with indiarubber ink eraser. The backs of
impressions may also be cleaned in the same manner.

When copies have to be mounted on cardboard they may be either left
with a matt surface or varnished. In the first case, the edges are
trimmed, and they are then mounted upon the cardboard mounts. If the
latter have been previously damped they will retain their flatness.

=Rolling or Burnishing= must not be done until the prints have
completely dried, or the picture may be torn from the mount.

=Sizing and Varnishing.=—Prints to be varnished may be printed on
prepared or sized paper, and in such cases may be at once varnished.
If, on the contrary, the paper is not sized, they require a special
preparation, as follows:—A 10 per cent. solution of gelatine is laid on
with a broad camel-hair brush, avoiding air bubbles and streaks. After
a little practice this operation will be found both easy and rapid. The
sized pictures are pinned in pairs back to back on a wooden frame, to
which strips of cork are attached; when the prints are quite dry the
operation of varnishing may be proceeded with. A good varnish, probably
the best for the purpose, which possesses the double advantage of
remaining colourless and setting very hard, consists of a solution of
15 parts of white (bleached) lac in 100 parts of wood spirit (vegetable
or wood naphtha). On dissolving the shellac it will be found that the
solution is clouded on account of the suspended fatty matter, the
removal of which is always desirable; the varnish will then filter more
rapidly and give a more glossy coating. By adding powdered lime three
parts of the solution may be decanted clear, and the remainder may also
be used after filtration through felt. Or if to three parts of varnish
one part of benzine or petroleum ether be added, the solution will
resolve itself into two layers, and the upper one, which will contain
the fatty matter, may be poured off. The varnish is best applied by
means of a ball or dabber, care being exercised to avoid air bubbles;
the print is next placed in

=The Drying-box= (see fig. 8), which is a four-sided tin box 1 m. long
by 0·25 m. high. A gas-pipe, perforated with small holes drilled about
6 to 8 cm. apart, runs through the upper part of the box, the front of
which is open to two-thirds its height. A plate, finely perforated,
divides the upper third from the lower two-thirds, and forms an inner
division, through the upper of which the gas-pipe passes. The flat
perforated division is hinged to allow of being opened for the purpose
of igniting the gas. The pictures placed on the bottom of the box dry
very rapidly, while the perforated division prevents the possibility
of the ignition of the vapour of the spirit employed. With such an
apparatus it is possible to varnish and dry a large number of prints in
a very short time.

[Illustration: _Fig. 8._]

=Sizing may be Avoided= if each picture, after well drying, be dipped
into the following solution: Water 500 g., borax 130 g., white shellac
100 g., carbonate of soda 6g. The borax and carbonate of soda are
dissolved in boiling water, and the powdered shellac then added in
small quantities; when solution is complete carefully filter and allow
to cool. The impressions, two and two, back to back, are pinned on
frames, dipped in the varnish, and afterwards dried. By this procedure
a shellac coating is given to the surface only of the print; there is
no gelatine substratum to soften through atmospheric influences, and so
crack and destroy the layer of varnish. In winter the temperature must
be kept high, and the solution should be heated 15° to 20° C.

=Parchmentising= to a slight degree may also be adopted to close the
pores of the paper. Add one part by volume of water to two parts of
sulphuric acid, allow it to become quite cold, immerse the pictures for
one second only, and at once wash in a copious supply of clean water
to which has been added a small quantity of ammonia to effectually
neutralise the acid. The action of the acid must not be carried too
far, as it is merely necessary to act on the surface. To prevent paper
so treated from cockling while drying, it must be put under pressure or
stretched upon a frame; when quite dry it has to be varnished and dried
by heat.

=Varnishing Enamel Paper= without previous sizing is best done by means
of an alkaline solution of shellac prepared as follows: Place in a six
litre tin flask 1/2 kilo of bleached and powdered shellac, pour over
it 1-1/2 kilo of alcohol and 1-1/4 kilo of strongest ammonia. In the
course of a few days the solution of the shellac will be complete,
then add, with constant stirring, 2-1/2 kilo of hot water, and when
cold filter. It may be applied to the print with a broad Blanchard
brush,[K] and left to dry in a horizontal position. The prints may also
be floated on the varnish for about half a minute, and then suspended
to dry by means of clips. After a few minutes have elapsed a piece
of blotting paper should be applied to the bottom edge to absorb the
superfluous varnish.

  [K] Made as follows: Take a piece of glass, say 20 cm. long by
      6 or 7 cm. wide, and a piece of swansdown calico the same
      width as the glass but only 6 cm. long, fold this over the
      one end of the glass, 3 cm. being on each side, and bind
      round with thread or spring on a rubber band.

=Rolling or Burnishing= must on no account be attempted until the
mounted prints are perfectly dry, otherwise they may be seriously
damaged or even completely torn from the mounts.




CHAPTER X.

OTHER COLLOTYPE PROCESSES.


=The Artotype Company=, of New York, which has acquired Obernetter’s
process, proceed on somewhat different lines to those laid down in this
work, and an abstract of their proceedings is here given as interesting
to those about to experiment. According to Bachrach, “Photographic
Archives, 1879,” p. 66, they proceed as follows:—

[Illustration: _Fig. 9._]

Plates coated with Husnik’s silicate of soda substratum are dried
rapidly in a box heated to 65° C. This causes the solution to
coagulate, the plates are dried in half-an-hour, and as it adheres with
great tenacity to the glass plate, the latter may be at once coated
with the chromated gelatine solution, or it may be kept till the next
day. Before the second coating is applied the plate is well washed and
allowed to dry spontaneously. The drying-box is of wood, 2-1/2 feet
square and 5 feet high, the entire front being a large door, as shown
in the sketch (fig. 9), and the bottom a flat water tank about four
inches deep fitted with two pipes, one to allow the escape of steam,
and the other of use in filling the tank with water. It may be heated
by means of gas or a petroleum lamp. After the bottom of the box has
been accurately levelled, it is covered with a few sheets of blotting
paper, on which are placed the albumenised plates. Occupying the upper
part of the box are adjustable racks, on which other plates are dried.
The box is heated to 82° C., the plates are levelled in their places,
and just sufficient hot chromatised gelatine solution poured on each to
spread up to the edges—not more. The Artotype Co. takes one-third each
of gelatine, isinglass, and the so-called Magdebourg isinglass. Plates
are allowed to remain in the drying-box about 20 to 30 minutes, during
which time the door must not be opened, and particular importance is
attached to the high temperature, reaching even to 93° C., at which the
drying is completed, as it is considered by these means printing plates
of much finer grain are obtained. (The Author believes the temperature
given is much too high, as it would be sufficient, without exposure to
light, to bring about a partial decomposition.) When dry, the plates
may at once be printed under the negative. To etch the plate it is
immersed in a solution of 5 gr. alum in 1 litre of water, rinsed,
allowed to dry, and put in a bath consisting of 150 ccm. of water, 1
litre of glycerine, 300 ccm. of ammonia, 30 g. nitrate of lime. Plates
that have been exposed under the negative too long are treated with a
solution of 20 parts of ammonia, 20 parts of glycerine, and one part of
Venetian turpentine; with this they are flooded. The remainder of the
process is very similar to that already described.

=Seignior Carlos Relvas.=—Vidal publishes the following method of
procedure as that adopted in the studio of this eminent Portuguese
amateur collotypist, where it was introduced by Jacobi:—Very thick
glass plates, finely ground on one side, are used; they are cleaned
with nitric acid, and rinsed in distilled water. The drying box used is
provided with iron bars, fitted with adjustable screws for the purpose
of accurately levelling the plates. Midway between the top and bottom
of the box is an iron plate, underneath which are fitted gas jets. The
doors by which access to the box is gained for the plates consists of
very fine wire gauze, allowing the escape of steam, but preventing the
access of insects. After a thorough cleansing, the plates are levelled
on the adjusting screws, allowed to thoroughly dry, and then coated on
the ground side with the following solution—

  White of egg               160 ccm.
  Bichromate of potassium      8 g.
  Distilled water            480 ccm.
  Glycerine                   16 drops.

To which is added sufficient ammonia to give the liquid a pale yellow
tint, somewhat less being used where a hard negative is to be employed.
This substratum is filtered, and the plates afterwards coated and
placed upon the levelling screws in the drying box, which is heated to
a regular temperature of 40° C. In about two hours the plates will be
dry, and are then placed, coated side downwards, upon a black cloth,
the back of the plate being exposed to diffused light for half-an-hour.
It is again placed in the drying box, and the second coating, as
follows, applied—

  Gelatine                    27 g.
  Water                      400 ccm.
  Bichromate of potassium      9 g.
  Preparation A               15 ccm.
  Preparation B               15 ccm.
         Ammonia a few drops.

The preparations A and B are as follow:

  A.—Chloride of sodium     1 g.
     Water                500 ccm.
  B.—Sulphate of alumina    1 g.
     Water                100 ccm.

To each square decimetre of surface should be allowed 2 ccm. of the
above solution. The plates are replaced in the drying box, which is
heated to 45° or 50° C. They should be dry in three hours, and are
then ready for printing under a negative in the copying frame. They
are afterwards well washed in filtered water, and allowed to dry
spontaneously in a dust-proof situation. In two or three days the
printing may be proceeded with, the surface having been softened by
allowing the plate to stand for seven hours in the following solution—

  Glycerine          500 ccm.
  Distilled water    200 ccm.
  Preparation C      100 ccm.

  PREPARATION C.—Sulphate of magnesia    50 g.
                 Distilled water        500 ccm.

All solutions are filtered through flannel. From the face of the plate
the superfluous moisture should be removed with a sponge. A very thick
glass plate is fixed to the face of a lithographic stone by means of
glue and whiting, and adhesion is secured between the face of the thick
glass plate so fixed and the back of the Collotype plate by means of a
few drops of water. The whole, so arranged, is placed upon the bed of
the press. Should the prints lose their contrast while the printing is
in progress, they are lightly sponged over with a sponge dipped in the
last-mentioned solution. If this fails to produce sufficient effect,
the plate is first washed with turpentine, and then with the glycerine
solution. Care should be taken to prevent the two liquids becoming
mixed on the plate, to prevent which different sponges and drying
cloths should be used.




CHAPTER XI.

FAILURES IN COLLOTYPE.


IN THE PREPARATION OF THE PLATES.

=Air bubbles= in the albumen substratum. These must either by
filtration or by the aid of a piece of paper be carefully removed from
the solution before it is applied to the plates. The latter must be
well cleaned and dusted, and freed of emery powder if they have been
re-ground.

=To Prevent Dust= or other matter rising from the edge of the plates by
capillary attraction while standing, they should be allowed to rest on
clean blotting paper, and preferably on one corner only.

=Coating Plates.=—Great difficulties are experienced by the beginner
in coating the plates with the chromated gelatine. He seldom knows
beforehand the exact quantity required, or the temperature of the
solution. The latter ought to be ascertained, as it is an important
factor in the thickness and flow of the coating; with a solution only
just warm it is impossible to apply a very thin coating, while the
hotter the gelatine the thinner the layer. Considerable dexterity
and judgment are necessary to spread an even layer of the requisite
thickness, which is a matter most essential to success, but,
unfortunately, only to be mastered by actual experience.

Plates are not unfrequently spoiled by inclining them while conveying
them to the drying box, as in this way the coating is frequently
rendered uneven.

All solutions must be carefully filtered, and the plates freed entirely
from dust. The drying box, particularly the lid, must be carefully
dusted and cleaned, but not immediately before use.

Other necessary precautions have been pointed out while describing
the preparation of the plates. By strictly adhering to the rules laid
down it will be found possible, after a certain amount of practice, to
avoid the pitfalls here enumerated, while with regard to faults in the
plates, there only remain to be mentioned the consequences of drying at
too high a temperature.

=Thick Films= are extremely liable to fly off the glass and damage its
surface, if dried at too great a heat. The thicker the film the lower
should be the temperature of the drying box.

=Thin Films=, dried at too high a temperature, even without exposure to
light, present a brown appearance, their sensitiveness is impaired, and
they take too much ink over their entire surface.


FAILURES IN PRINTING.

It is generally an advantage to work the press in a cool and somewhat
damp apartment.

=Breakage of the Plate.=—Notwithstanding its thickness, the glass
plate sometimes flies to pieces on pulling the first impression. If
the plate and its foundation are perfectly level the breakage must
arise from the presence of some foreign substance having found its way
between the two surfaces.

This may occur from such a trivial matter as a grain of sand, perhaps
introduced between when moistening the under side of the plate to
secure adhesion. Or traces of chromated gelatine may be found attached
to the under surface of the plate, either of which causes is quite
sufficient to account for a breakage with even moderate pressure.
In Collotype the pressure need not be by any means so heavy as in
lithographic printing; it should be evenly distributed, and may
be moderated by placing the stone or glass plate, or whatever the
Collotype plate may be attached to, on some comparatively elastic
bedding, which may consist of several layers of printing paper, thin
felt, thick indiarubber sheeting, or linoleum, any of which may be used.

=Spotted Impressions.=—The plate yields unsatisfactory copies covered
with white spots resembling drops of water. This most frequently occurs
at the commencement of the printing, and is nearly always caused by
uneven damping of the surface. Old plates which have been dried very
often give perfect negative impressions at first. In such cases, after
the removal of the ink by turpentine, soak the plate for a quarter
of an hour in water, to which has been added a little glycerine and
ammonia (see “Etching Fluid”). Dry the plate with a clean roller
covered with cloth or chamois leather—or, as a substitute for the
roller, a soft linen cloth may be used—and again roll in with ink which
has been thoroughly well distributed on the inking slab.

=Too Much Ink= is taken by the plate over the whole surface, and
notwithstanding slow or rapid rolling, it refuses to leave the high
lights. Cause—over-exposure in proportion to the thickness of the
layer, which is probably too thin. In such cases washing with dilute
solution of ammonia will often improve matters. Another proceeding
to be recommended in the case of a plate taking too much ink is to
remove all ink by means of a sponge damped in water containing a little
petroleum—not benzine or turpentine—and afterwards wash the plate with
a sponge containing glycerine and water. It is then ready for immediate
printing from, and ought to give about 200 copies without further
damping if the press be in a moist situation.

=Loss of Half-tone= arises from the print layer becoming too moist,
when the more delicate half-tones fail to print. Dry with blotting
paper, and immerse for five minutes in a bath of alcohol; this will
take up the water, and the succeeding impressions will be greatly
improved.

=Uneven Inking.=—It sometimes occurs, particularly in pictures which
should show a white ground, that the latter takes more ink in one part
than another. This usually arises from an unequal thickness of the
sensitive coating. The plate will take most ink where the coating is
thinnest, and for this fault there is no remedy.

=Ink Refused by the Plate.=—Sometimes, after a few impressions have
been pulled, the plate refuses to properly take the ink, from the layer
being too thick and having been too freely moistened. Further damping
should be discontinued and a thinner ink used, which will better take
upon the deep-lying shades. This fault will be found most pronounced
in the cases of written or printed titles to pictures, and other cases
exhibiting extremely disproportionate action of light. Therefore, when
there is writing to a picture, it should be shaded somewhat during
printing in the printing frame, or if the contrast be very violent it
may fail to print entirely.

=Flat Prints.=—After a number of satisfactory prints have been produced
the succeeding ones become flat, this fault will be especially
noticeable with thin layers devoid of isinglass, and in cases where the
negative has been too flat and lacked contrast. Dampen more frequently
with dilute ammonia and glycerine.

=Paper Adhering to the Gelatine=—Those layers which yield the best and
most brilliant impressions, showing plenty of contrast, which have
been fully printed under a vigorous negative, most often exhibit a
disagreeable tendency to adhere to the paper in the high lights. The
greater the proportion of isinglass present in the film the more will
this fault manifest itself, particularly with an enamel paper. An
application of a diluted solution of ox-gall to the film, the use of a
thick well-sized or glazed paper, lighter pressure while printing, and
less frequent damping will all tend to diminish this evil. Layers of
this nature are extremely liable to damage, and the adhesive portions
will soon suffer unless the greatest care is exercised.

=Ink Remains upon the Plate.=—Through too light or uneven pressure it
sometimes happens, especially when using a stiff ink, that the latter
will, after the impression has been pulled, partially adhere to the
darkest portions of the printing surface, particularly on the edges
of plates deeply copied. If this fault is not corrected at once, and
the printing allowed to proceed, these portions giving a light, faulty
impression will gradually increase in size, and the corresponding
portions of the Collotype plate gradually darken. When first observed
the whole plate must at once be cleaned with turpentine and again
rolled up with thinner ink, a greater and perfectly even pressure being
applied. Small faults of this nature occurring on the edges of the
plate can be corrected after each faulty impression by means of a small
piece of sponge moistened with gum water or with a turpentine rag.

=Displacement of the Paper= under the scraper will create a double
impression, and sometimes wrinkles, the latter invariably leading to
the destruction of the plate. By adopting the use of the bridge now
used in conjunction with most Collotype hand presses, this fault is
avoided, as the paper is only in contact with the printing surface
immediately under the scraper.




CHAPTER XII.

INVESTIGATIONS ON COLLOTYPE.


August Albert[L] is of opinion that it is by no means a matter of
indifference whether bichromate of potassium or bichromate of ammonia
is used in the preparation of the Collotype plates; on the contrary,
he believes that the latter salt materially conduces to interruptions
in printing, especially in unsettled weather. The results of his
experiments with the two salts in the Collotype process, and of their
behaviour in combination with different sorts of gelatine, are as
follows:—

To 1000 cc. of water are added ten drops of a saturated solution of
chrome alum; this mixture, after having stood for a quarter of an hour,
must, if shaken up, show an opalescent appearance, and a slight milky
turbidity; if too much chrome alum has been added, the water acquires
a greenish colour. The gelatine is now added, and, for about fifteen
minutes, kept at a temperature of 134°, when the chrome salt is added,
stirring all the while, and the temperature of the water bath raised
to 150° to 160°. The temperature and time must strictly be adhered
to. The jelly thus prepared should be kept at least ten hours in a
solidified state previous to using.

  [L] This experimentalist has evidently been confused with the
      late Joseph Albert, of Munich, by some writers. It may be
      mentioned that Joseph Albert, whose business is still carried
      on by his widow, was father of Dr. Eugene Albert, known in the
      photographic world for his orthochromatic collodion emulsion.
      August Albert, of Vienna, is of another family.

=Hard Gelatine.=—Plates prepared with this, show after drying, a shiny,
transparent film, more or less according to the quality. Such plates
give hard prints, and are soon used up in printing, the finest and even
the middle tints becoming weaker, and the shadows gradually coalescing,
specially in the case of short exposure and very dense negatives, and
they are generally useless after a few impressions have been taken. If
ammonium bichromate is used, together with hard gelatine, then, as a
general rule, it is impossible to obtain more than one or two prints
from each plate. By washing the gelatine, these inconveniences are not
at all removed, no matter which of the two salts has been used.

=Soft Gelatine.=—If this is prepared with potassium bichromate, then
the plates will have a dull but rough and untransparent film, which
will be found very unserviceable for printing, as the prints will
lack vigour; the high lights will tone, and the whole picture appear
blurred. If, however, ammonium bichromate is used in conjunction
with soft gelatine, the plates will also have a dull appearance, but
though they work somewhat better than those prepared with potassium
bichromate, they will not be of sufficient durability, the finer tones
soon disappearing during printing. Therefore, neither hard nor soft
gelatine are suitable for Collotype work, as the printing operations
are rendered more difficult. If both sorts are mixed, the results
will be somewhat better, but not like those obtainable with middle
hard gelatine, which must be accepted as the most suitable kind for
Collotype work.

=Middle Hard Gelatine=, manufactured by Ferd. Friedr. Creutz,
absorbs five times its own weight of water at 66°, without signs of
disintegration after standing therein for thirty-six hours. If prepared
with it and with chemically pure potassium bichromate, the plates
after drying have a beautiful matt surface, from which long numbers
can be printed without any falling off of the half tints, and, if the
printing is done carefully, even the details in the shadows will be
maintained to the last. This bichromated gelatine requires also only a
very small amount of re-damping, reproduces faithfully the character
of the negative, and the jelly can be used even after a period of four
days. If, however, the work in hand requires a harder bichromated
gelatine—as, for instance, reproductions of black and white—then the
addition of a small quantity of ammonium bichromate will have the
desired effect; in some cases equal quantities of the bichromates of
potassium and ammonium. If ammonium bichromate is used instead of
potassium in conjunction with middle hard gelatine, then the plates
will acquire a shining, transparent coating, the manipulation of
which is very difficult in printing, and which work too hard, being
serviceable, at any rate, for reproductions without half-tint. If,
however, the middle hard gelatine is washed before use, it will give,
when mixed with the chromic salt, transparent films of insufficient
durability. Middle hard gelatine should therefore be used unwashed for
Collotype work, and mixed with chemically pure potassium bichromate.

=The Production of Grain= in Collotype plates takes place in the
last instant of drying the plates in the drying-cupboard; it depends
entirely upon the larger or smaller quantity, and the consistency of
the bichromated gelatine used. If the latter is of good quality, all
artificial means for the production of grain are not only superfluous,
but also disadvantageous. A larger addition of chrome salt generally
gives rise to the crystallisation of the salt; chloride of sodium
produces plates highly sensitive to moisture, but no grain; a larger
addition of chrome alum gives plates which will lack vigour, and the
manipulation of which, during printing, will be difficult, as they
often will require an “after-etching,” so that even printing is made
impossible.

To test the suitability of gelatine for Collotype work, two small
portions of the gelatine to be tested may be made up, adding chemically
pure potassium bichromate to the one, and ammonia bichromate to
the other, and a plate prepared with each solution. If both plates
show a dull and untransparent coating, this indicates that it is a
soft gelatine; if, on the contrary, both plates appear glossy and
transparent, then the gelatine is hard. Should it, however, be middle
hard, then the dried film prepared with potassium will be dull, but not
rough; that with ammonia, however, shiny and transparent.




CHAPTER XIII.

COLLOTYPE IN NATURAL COLOURS.


A short chapter may be devoted to the various suggested processes for
producing Collotype in natural colours, with which are associated the
names of Vidal, Albert, and Obernetter. To give a complete _resume_
is altogether impossible, as up to the present time the inventors
have only published their method of procedure with very considerable
reservations, and notwithstanding the fact that a great deal has been
written and published in current literature on the subject, little is
actually known. The methods of Vidal and Albert are essentially alike,
both being founded upon an opti-chemical basis. By careful registration
and printing from three Collotype plates, representing fragments of
the same subject upon one sheet of paper, and making use of inks
corresponding with the three primary colours, a total effect should be
produced which ought, theoretically, to resemble the coloured original.
In preparing the three negatives for reproducing the three colour
plates a special mode of procedure must be adopted. Each of the three
negatives must give a resulting Collotype plate capable of retaining
varying amounts of ink when rolled up, according to the predomination
in the original of one or the other of the primary colours—red, blue,
or yellow.[M] This is effected in the production of the negative for
the red plate, by making the exposure through a green glass screen,
while the negative intended to produce the plate from which the yellow
is to be printed is exposed through a screen of violet.

  [M] Pictures produced in the three primary colours are extremely
      crude. Dr. Vogel has proposed a large number of negatives,
      using for their production sensitisers corresponding with
      every region of the spectrum. For example—Napthol blue for
      red, cyanin for orange, rozin for yellow, and fluorescein for
      bluish green, the ordinary sensitiveness of the plate being
      sufficient for blue and violet, the latter, however, being
      exposed through a yellow screen. The images thus obtained are
      printed from lithographic stones or Collotype plates, each
      of which is printed in a colour complimentary to that part
      of the spectrum to which the particular plate was sensitive.
      The greater the number of separate images produced in this
      way the more complete will be the reproduction of the various
      shades in the original, and the more pleasing the resulting
      print.

The green screen allowing to pass so few chemically active rays the
exposure has to be prolonged to such an extent that gelatine bromide
dry plates stained with eosine must of necessity be used.

Obernetter’s method is entirely different, depending more upon
mechanical assistance of a non-photographic character in the production
of the unlimited number of negatives he uses for producing his
printing surfaces, and the results more closely resemble those of
chromo-lithography. What particulars Obernetter himself has from
time to time communicated are here given. He first produces, by the
dusting-on process, as many copies of the original negatives as
there are colours to be reproduced. The negative intended to produce
the plate from which the blue will be printed is obtained by a long
exposure and only slight dusting of the reproduced negative. That
intended to reproduce the plate for the non-actinic colours—yellow or
brown—should be correctly exposed and dusted in; while that intended
for the red should be subjected to a shorter exposure and more vigorous
dusting. By retouching, the densities of the various negatives may
be modified by strengthening them in parts, other portions are
stopped out, and the negatives so manipulated that they will produce
plates capable of giving impressions—when printed in their proper
colours—giving a facsimile reproduction of the original work. Much will
depend upon the artistic qualifications of the operator, who may, by
extending the number of plates, finally produce copies of considerable
artistic value.

Hösch, of Munich, has patented a process in which the same result is
attained in a somewhat different manner. A negative is produced, and
from that a Collotype plate from which a number of impressions are
taken equal to the number of printing desired or necessary in the
finished chromo-collotype picture. Each print has certain portions
painted over in a neutral tint, such portions depending upon the colour
of the ink in which it is intended to print the corresponding plate.
Other portions are stopped out white in the print, or black in the
negative, and from the prints so treated a set of negatives are taken;
these are utilised for the production of a set of Collotype plates,
which, printed from in suitable colours, yield impressions of great
excellence.




CHAPTER XIV.

MAGIC PRINTS.


To Professor Husnik (to whom collotypists are greatly indebted for
so many unselfish publications), we owe the origination of this
interesting method of producing “magic” prints. It is founded on the
reaction well known to chemists that two substances, each colourless
in itself, when mixed, enter into fresh chemical combinations and
produce other substances of intense colour. Herschel and Hunt made
use of many of these reactions, both to develop the invisible image,
and to give to others, already visible a more agreeable colour or
tone. Impressions other than those in fatty ink may be obtained from
the Collotype plate—as in the process patented by Edwards—by means
of colour, soluble in water, to which the addition of a small amount
of gum has been made. In such cases it will not be those portions of
the layer which have been rendered insoluble by the action of light
which will give the impression (as it would if ink were used) but on
the contrary, the unexposed parts, or those which remain soluble. On
this account the resulting print will be a negative, and to obtain a
positive, the printing must take place under a positive. If a Collotype
plate so produced be damped with a linen rag which has been moistened
with an aqueous solution of a salt readily absorbed by gelatine, and
which will produce in combination with a second solution an intensely
coloured compound (the use of the ink roller being entirely omitted),
the impression on the printing paper will be almost or even entirely
invisible until brought in contact with the second solution, when
the picture will be immediately developed and rendered visible. For
instance, dampen the plate with an aqueous solution of red prussiate of
potash, surface dry it, print upon paper, allow to dry thoroughly, and
place upon a solution of protosulphate of iron, when the picture will
immediately appear of an intense blue colour. Solutions of bichromate
of potassium or nitrate of silver will produce brown images; the
former developed with extract of logwood, alazarine or sugar of lead,
all produce different colours. Not only is this process interesting,
applied in the manner already described, but it is of use in calico
printing. Care must however be exercised in the selection of a suitable
solution for damping the plate, as many salts would tan the gelatine
layer, and such are of course utterly unsuited for the purpose. Among
the mordants in common use, salts of tin, alum, iron, &c., may be
mentioned as exercising a hardening influence upon gelatine, and
therefore useless for moistening the layer. There remain, however, many
others which produce no damaging effect upon the plate, and at the same
time produce useful colours.




CHAPTER XV.

PHOTO “GLASS” PRINTING.[N]

  [N] This process has never been practised in this country so far
      as I am aware.—TRANS.


There remains to be mentioned another variation of the Collotype
process known under the above vague title, the distinctive
characteristic of which method of preparing the plate is that the
negative is taken upon a sheet of glass sufficiently thick to stand the
necessary pressure in printing when converted direct into a Collotype
plate. After the completion and drying of the collodion negative it is
coated upon the film side with the chromated gelatine solution, dried
in the drying-box, laid face downwards upon a black velvet surface, and
exposed through the back of the glass. The first publication of this
method of preparing plates emanated from the State Printing Works at
Berlin, and the following is an outline of the method there practised;
it is scarcely necessary to state that it is only available for line
subjects. The collodion used in the preparation of the negative should
be one capable of producing clear, hard negatives entirely free from
fog; probably some modification of the dark slide may be necessary to
enable it to receive a plate of sufficient strength to stand printing
from. The collodion negative being completed it is flooded with the
chromated gelatine as applied to Collotype plates, dried, and exposed
through the negative until the print layer has assumed a dark brown
colour; it is well washed in cold water and damped before printing by
an application of gum water containing a little ox-gall; this is done
to facilitate the production of perfectly clear impressions. The same
end may be attained by the application of dilute ammonia and glycerine.
The author has experimented for several years in the same direction
with the object of producing heliographic printing plates in copper,
for which purpose this method of producing reliefs in gelatine is well
suited. From the negative printing plate described, which is treated
in all respects as a Collotype plate, impressions may be taken upon
transfer paper, and transferred to stone or zinc. Before coating the
negative with the chromated gelatine the plate should be allowed to
dry. In consequence of printing from the back the lines will always be
slightly wider than the original, to meet which difficulty Brandt has
proposed putting the negative, when fixed and washed, but still wet,
into a weak solution of chromated gelatine, which will, if a suitable
collodion has been employed, entirely penetrate the latter. This
variation appears worthy of commendation; it is, therefore, here given
in the abstract:—“Having produced a negative in the usual manner, on
a plate which has been lightly but carefully albumenised, and having
fixed and washed the same, it is placed for five minutes in a solution
prepared as follows: Allow 45 parts of gelatine to swell in water,
and pour off the surplus, add 50 parts of distilled water, and apply
sufficient heat to completely liquify the gelatine, adding a solution
of 5·5 parts of bichromate of ammonium in 100 parts of water, and heat
again to 60° Réamur. With plates of large size the solution may be
poured over the plate, and it may be necessary to repeat this operation
several times to ensure an even and sufficient coating. Immediately
previous to the application of the chromated layer the negative should
be rapidly washed over with warm water. A sufficient quantity of the
chromated solution must be allowed to remain upon the plate, and the
latter warmed in a horizontal position over a spirit lamp. When steam
arises the plate has to be held in a perpendicular position for a
minute, restored to its horizontal state, and again warmed until the
coating of the plate is quite dry, care being taken that at no time
the plate is so heated that it becomes unpleasant when placed upon the
hand. Place the plate face downwards upon a black support, print until
the fine lines are plainly visible, when the plate may be washed and
further treated as in Collotype.”




CHAPTER XVI.

ALLGEYER’S COLLOTYPE PROCESS.


=Half-tone Negatives= must be softer, and possess more half-tone than
requisite for silver printing. When examined by transmitted light, they
should appear clear in the shadows, and not too dense in the half-tones.

=Line Negatives.=—Negatives for the reproduction of line subjects need
not possess the absolute opacity requisite for silver printing, but the
lines should be clear glass, entirely free from fog or deposit.

=Stripping the Negative.=—The fixed and washed negative is flooded over
with a solution of gum arabic in water (1 to 20), to which has been
added a few drops of a solution of chrome alum (1 to 60). Allow to dry,
retouch with lead pencil, and edge with tallow to prevent overflow,
place upon a levelling stand, warm moderately, and coat with a solution
of gelatine 100 parts, glycerine 15 parts, alcohol 100 parts, water 400
parts, allow to set, and place against a wall to dry, the coated side
outwards, the plate standing upon clean blotting paper. The operation
of drying will probably take a day or two, and when quite complete,
it is again coated with collodion, and again dried. After allowing to
remain in a damp place for two or three hours, cut around the edges
with a knife, and strip off the film, which may then be printed from
either side, and after use may be stored in a book, the leaves of which
consist of smooth paper.

=Reproduced Negatives.=—Coat a plate with a solution of gum arabic 50
parts, dextrine 50 parts, honey 10 parts, sugar 25 parts, glycerine 5
parts, bichromate of ammonium 15 parts, ammonia 50 parts, water 1,000
parts. After drying, expose under a negative, dust over with graphite,
coat with plain collodion, and wash in clean water until all yellowness
disappears.

=Substratum.=—(1.) Water 300 parts, white of egg 300 parts, ammonia
50 parts. (2.) Water 300 parts, gelatine 10 parts, bichromate of
potassium 10 parts. Filter both solutions, and mix, taking care that
the temperature never exceeds 32° C.; pour upon glass plates heated to
30° C., and dry at a temperature of 22° C. After thoroughly cleaning
the back of the plate, place, face downwards, upon a black cloth, and
expose to light through the glass till the coating becomes brownish.
To test if sufficiently exposed, dampen a portion of the film with
the finger, scratch with the nail, and the scratch should stand out
perfectly sharp.

=The intermediate layer= is to ensure the better adhesion to the glass
of the print layer proper, and to facilitate the retention of moisture
while printing. It consists of gelatine 100 parts, water 1,500 to 1,800
parts, alcohol 150 parts, glycerine 5 parts, bichromate of potassium 5
parts. This is spread over the substratum, allowed to dry, and exposed
to diffused light, or allowed to stand for twenty-four hours, well
washed, and allowed to dry spontaneously, after which it may be kept
for weeks.

=The Print Layer= consists of water 1,500 parts, gelatine 100 parts,
bichromate of ammonium 30 parts, complete solution being effected by
means of a water bath; the drying box heated to 45° to 50° C. Place
the levelling stand upon a sheet of white paper, carefully dust and
accurately level the glass plate, and coat, using 30 ccm. of solution
to cover 25 × 35 cm. of surface, avoiding any overflow of solution.

=The Washing Water= used after printing in the copying frame should not
exceed 22° C. in the summer, or fall below 10° to 11° C. in the winter.
Washing should be continued until the film is free from colour, and a
final rinse should be given under a rose. Allow to dry slowly.

=Etching Solution.=—Water 500 parts, glycerine 500 parts, chloride of
sodium 15 parts, or hyposulphite of soda 15 parts.

=Rolling Up.=—If the picture take too much ink, wash off with
turpentine, carefully wipe with a cloth, and continue the etching. If
it take little, wash off the ink with etching fluid, and place in a
hardening solution of chrome alum 1 part, water 6 parts, wash, dry, and
once more etch for a quarter of an hour.

=Varnish for Prints.=—Bleached shellac 100 parts, dissolved in alcohol
300 parts, adding ammonia 300 parts, further adding, with constant
agitation, 600 parts of boiling water.




CHAPTER XVII.

PRACTICE OF PHOTO-LITHOGRAPHY.


In photo-lithographic operations, quite a different set of conditions
has to be considered as compared with Collotype. An explanation is, of
course, not far to seek, as both the chemical and physical properties
of the lithographic stone and the exposed chromated gelatine layer are
so extremely different. To the better understanding of the operations,
the composition of the lithographic stone and the principles underlying
the process may be first considered.

Senefelder is a name inseparably connected with lithography, as it
was he who, after a continuous and laborious research, discovered the
remarkable properties of the Solenhofen limestone, who thoroughly
worked out the conditions under which printing with fatty inks could
be carried out, and so thorough and conclusive were whose researches
that the process as now practised may be said to be actually identical
with those of the discoverer. He was by inclination a dramatic author,
but failing to find a publisher for the productions of his brain, he
conceived the idea of publishing his own works. At a printer’s he
acquired the necessary knowledge to perform the work, but lacked
the funds to purchase press or type. He then turned his attention
to copperplate, made many unsuccessful attempts with an old one he
possessed, and when that was unfit for further experiment, extended his
operations to the pewter plates of his mother’s dining service, but
still without success.

By accident, his next experiments were made upon a stone procured from
Cellheim (Solenhofen), and which up to the present had served him as
a slab for his ink. For want of paper and ink to write a domestic
account for his mother, he casually used the surface of this stone in
lieu of paper, using as an ink a mixture of soap, wax, and soot, with
the intention of copying upon paper later on. When about to clean the
slab, the thought flashed across his mind why not etch the stone with a
dilute solution of nitric acid? The experiment was tried, and succeeded
beyond expectation. Upon this simple accident has been built up the
whole process of lithography. It was only in 1799, after a prolonged
and severe struggle, that he was granted protection for his art in
Bavaria.

The acid etches away a very thin layer of the unprotected stone,
while the writing is not attacked, but left slightly in relief.
Senefelder—first with a dabber, and later with a piece of wood covered
with cloth—inked in the writing, and so produced impressions, the
earliest of which were sheets of music. The etching of a lithographic
stone bearing a drawing or transfer in lithographic ink has a twofold
action, each of which facilitates the printing. In addition to the
slight relief already mentioned, as resulting from the application
of the acid, the latter forms upon the surface of the stone, where
attacked, nitrate of calcium, which resists and refuses the fatty ink
upon the surface of the roller, and if the surface of the stone be kept
constantly damp it becomes possible to roll up the drawing, to which
alone the ink adheres.

Lithographic stones do not consist merely of carbonate of lime, but
contain also silica, alumina, and some iron; the colour is a useful
indication of quality, those presenting a bluish grey appearance
being most highly prized, while those of a yellow colour are somewhat
inferior. The stone may be split into various thicknesses, and prepared
for use by grinding either one or both surfaces. They are placed face
to face, and the first grinding is completed with coarse sand, for the
second grinding a finer sand is employed between the two surfaces, and
this is succeeded by a grinding with pumice stone and water, the stone
being finally polished with snake stone. The so-called lithographic
chalk, with which the drawing on stone is sometimes executed, is
composed of finest lamp black (merely added for colour), soap, wax,
tallow, and shellac; during the etching, these ingredients undergo a
change, and form with the stone a chemical compound of great stability.
Since the fatty acids of the soap and tallow-namely, oleic and
margaric acid—set free by the nitric acid, combine in the nascent state
with the lime to form oleo-margarate of lime. This adheres tenaciously
to the stone, and the whole picture may, by the application of
turpentine, to all appearances be completely removed from the stone. If
the ink roller be again applied, it will be found that even the finest
details remain intact, and will reappear of their original strength,
the ink only adhering to the oleo-margarate of lime, and not to the
surface of the stone, which owing to the etching is wet with nitrate of
calcium.

This is the theory of lithographic etching and printing, to which it
has only to be added that soap and tallow must always be present in the
inks or chalks used in drawing to produce the combinations referred
to. Wax and shellac are only present as binding material. Transfer
ink, as used in photo-lithography, must be slightly thinned, and this
is best done by means of turpentine, and, if necessary, the occasional
addition of a few drops of olive oil. Should the ink be too stiff, or
be allowed to dry too much upon the transfer paper, the transfer will
probably be faulty, as the ink will only partially leave the paper. If
the ink remains in a soft condition it will be absorbed very readily
by the clean dry litho stone (not etched). Owing to the avidity with
which all grease is absorbed by the stone, it is necessary to keep it
perfectly free from all such contaminations. To keep the stone in a
clean condition while printing it must be etched, kept damp during
working, and, on completion or suspension of work, the surface should
be coated with a thick solution of gum arabic. Before resuming printing
operations, it is of course necessary to remove the gum from the
surface of the stone, which is done with a damp sponge.

As an introduction to the practical work of lithographic transferring
and printing the following description of the autographic method
will be found of interest, especially as it bears some similarity
to the more difficult process of photo-lithography, and enables
everyone possessing a lithographic press and stones to print their own
circulars, price lists, &c.




CHAPTER XVIII.

AUTOGRAPHY.


There are several methods of transferring from specially prepared,
or even any strong well-sized paper.[O] As the latter may be most
convenient, proceed as follows: Write with autographic transfer ink,
readily procurable from dealers in litho requisites; this will keep
for years, and may be used with any clean steel pen. After the writing
has dried, damp the back of the paper with dilute nitric acid—1 to 3
of water. When the writing is visible through the back of the paper,
the sizing has been acted upon sufficiently; the sheet should be placed
in a porcelain dish, washed in several changes of water, and blotted
off, leaving it evenly damp without being exactly wet. In the meantime
a stone should be adjusted upon the bed of the press, rubbed over
with pumice powder, and warmed—this may be easily effected by pouring
spirits over the stone and igniting it. A suitable scraper—one which,
when pressed against the stone, allows no light to pass between, and
which should not be wider than the stone—is adjusted in the scraper
box. The screw or other appliance for regulating the pressure is then
adjusted. The transfer is carefully and accurately placed upon the warm
dry stone, with the writing or drawing face downwards in contact with
the polished surface, a few sheets of waste paper are placed over the
whole, the tympan (the upper surface of which has been freely rubbed
with tallow) is lowered into position, the bed is then pushed, with the
stone so covered, under the scraper box, so that the scraper may come
down, not upon the extreme edge of the stone, but about four or five
cm. from the end, lower the scraper (or, according to the construction
of the press, raise the bed) and pull through under gentle pressure.
Release the pressure of the scraper, withdraw the bed, and raising the
corners of the waste sheets used as backing paper, convince yourself
that the transfer is in a proper position and has not moved; replace
the covering paper, change the position of the stone so that it passes
under the scraper in a reversed position, pass through the press again,
this time with greater pressure. Repeat these operations three or four
times, on each occasion under steadily increasing pressure; remove the
transfer carefully by one corner, and allow the stone to become cold;
sponge over with thick gum solution, and in this condition it may be
left for any length of time. Great care must be taken that none of the
tallow used on the tympan, or other grease, comes in contact with the
stone, either by the hand, covering paper, or other means.

  [O] Transfer paper is more reliable.

If the transfer should exhibit any signs of weakness while the stone
is still covered with plain gum water, take, upon a small linen pad, a
little ink thinned either with tallow or a few drops of turpentine; by
careful rubbing in different directions the lines will be considerably
strengthened. Plenty of gum must be kept upon the surface of the stone
during this operation, at the completion of which it may be removed
with a sponge and water, and the inking-up completed with the roller
and the stone gummed in.

Before printing, the gum has to be removed by water, and the stone
rolled up with a moderately stiff ink; it is then etched with gum water
rendered slightly acid by a few drops of nitric acid. The best test for
the acidity of this solution is to add just so much acid to the gum
water that, after its application to the edge of the stone for two or
three seconds, scarcely perceptible bubbles of carbonic acid gas will
show. This is applied evenly to the drawing with a sponge, and allowed
to act for a few seconds.

Should the ink “take” to the stone in places other than the design or
writing, rub the spot at once with woollen material moistened with gum
water; this will clear away the superfluous ink, but the part should
be carefully watched during the printing for any recurrence. After the
removal of each impression the stone is damped over the whole surface
with a damping cloth before another application of the inking roller.

For the production of perfect impressions avoid contact of the hands
with the face of the paper or stone, and care must be exercised
that all matters connected with the printing are kept scrupulously
clean, any contamination of a fatty or greasy nature especially being
strenuously avoided. The paper used in lithographic printing is usually
slightly damped by placing between sheets of damp blotting paper; such
proceeding is not absolutely necessary, as dry sized paper may also be
used.

The above detailed description of the necessary sequence of operations
in the Autographic transfer process will assist in understanding that
of photo-lithographic transfer, which requires still more care, and the
use of a special transfer paper so prepared that it is sensitive to
light.


THE BITUMEN METHOD.

This, the earliest photographic process, was discovered and described
by Niepee even before the discovery of photography or silvered plates.
It depends on the peculiar property asphalt possesses of losing its
solubility in ether, benzine, or turpentine after prolonged exposure
to light. If it be dissolved in turpentine in a photographically
dark room and the solution poured upon a well-polished metal plate
or lithographic stone, dried, and exposed under a reversed negative
(otherwise the impression yielded in printing will be reversed)
for two or three days[P] in sunlight, the picture may be developed
with turpentine or benzine, either of which solvents will remove
the layer from such portions as have been unexposed to the light
and reveal a picture in asphalt that may be rolled or inked-in and
capable of withstanding etching. This direct process, as applied to
photo-lithography, is now of little practical value owing to the
introduction and perfection of the transfer process. It is, however,
most valuable in heliographic engraving or etching and for the
production of zinc and copper printing plates.

  [P] The bitumen most suitable is that variously known as Syrian
      asphalt, Jew’s pitch and bitumen of Judea. This is finely
      powdered and placed in a bottle with twice the bulk of ether
      and occasionally agitated for five hours, at the end of
      which time the ether may be poured off and fresh supplies
      added so long as any portion soluble in the ether remains.
      The purified residuum maybe dried and dissolved in benzole
      or chloroform; this will yield a solution which may be
      used as above, but poisoning, perhaps, twenty times its
      sensitiveness. The picture is developed with turpentine.


DIRECT PHOTO-LITHOGRAPHY.

This method is little known, and it may be said that it has never been
developed to a practical issue. It is here only incidentally referred
to, but at the same time the fact may be pointed out that these two
direct photo-lithographic processes possess a value, inasmuch as they
may be utilised in a comparatively easy manner for the production of
grained or half-toned pictures, presenting less difficulties than by
the transfer process.

On to a well-cleaned stone, the surface of which may be either finely
grained or polished, a solution of gum arabic and bichromate is spread,
dried in the dark, and exposed for a sufficiently long time under a
negative; if the latter be a film it will facilitate the examination
from time to time of the progress of the copying. On completion of the
exposure the stone should be well washed with water and rolled in with
ink.

Morvan’s process is of a similar nature; a stone is coated with an
admixture of albumen 200 g., water 300 g., bichromate of potassium
50 g., dried and exposed under a stripped or paper negative. The stone
is then first washed with soap, and afterwards distilled water, and
then rolled up, gummed, and the ink allowed to set awhile, after
which printing may be at once commenced. In none of these methods
is mention made of etching the stone after inking-in, as is usual
in lithography; it may be here noted that photo transfers will not
withstand so vigorous an etching as drawings executed upon stone in the
usual manner. A photo-lithographic transfer may be quite ruined, even
entirely destroyed, by careless etching; this is therefore a point of
great moment, and one which has not usually been considered or dealt
with in published methods of procedure. We shall have occasion to again
refer to it.


PHOTO TRANSFER FROM PAPER.

In this method, now universally employed, success may be said to depend
more particularly upon two points. (1.) The paper for the transfer.
(2.) The suitability of the negative for the purpose in view. The
properties and preparation of a suitable transfer paper demand a few
words. It should be of substantial body, smooth and well sized; that
known as bank post is usually employed in this country. Professor
Husnik in his patented process proceeds as follows: 1 part of finest
gelatine is swelled, and then dissolved in 24 parts of water a solution
of chrome alum 1-100 in water is added, and the solution while still
warm is poured into a large zinc dish heated to 34° R. by means of
a petroleum or spirit lamp. Remove any scum from the surface of the
solution, float the paper one sheet at a time, and suspend to dry. The
sheet is floated upon the gelatine solution a second time, and once
more suspended, this time by the diagonal corner to that by which it
was previously hung. Prepare a solution of white of egg 1 part, water
2 parts, and on this float the paper on one side. After again drying
it is ready for sensitising, for which operation prepare a bath of
water 14 parts, bichromate of potassium 1 part, methylated spirits 4
parts, adding sufficient ammonia to turn the reddish solution a bright
yellow. If the paper is not prepared in large quantities, but only
for immediate use, the ordinary gelatine paper of commerce[Q] may be
employed with advantage, if further prepared by floating upon a bath
of albumen (beaten to a froth and allowed to stand) 50 parts, water
50 parts, bichromate of potassium or ammonium 7 parts (Märkl), upon
which bath the paper should be floated for five minutes. This solution
is subject to the disadvantage that even in the dark it will not keep
for more than a day or two, therefore it must be used at once. All
photo-lithographic transfer papers, after sensitising, should be used
within a few hours of their preparation or their good qualities are
partially sacrificed, the solubility of the albumen layer in cold water
being impaired. Photo-lithographic transfer paper prepared as above
described has been for some time in the market, and may be procured
as an article of commerce, in an unsensitised condition; it will keep
indefinitely in this state, and may be sensitised as required. The
surface should not be allowed to remain in contact with the bath,
neither should the immersion be lengthy, as in either case the surface
of the paper would probably suffer. After drying by suspending by one
corner in the dark, the chromated paper is exposed under a suitable
negative—if possible to the sun—for a few minutes only; it may be
examined by non-actinic light, and when the image appears brown or grey
upon a yellow ground, and all details are visible, it is removed from
the copying frame and entirely covered with a thin coating of transfer
ink. This as purchased is much too stiff for use, and must be reduced
by means of turpentine to such a consistency that it is possible to
distribute an even and quite thin layer upon the surface of the print,
without its penetrating to the paper. The ink should be so thin that it
presents a grey, not black, appearance.

  [Q] For instance, the double transfer paper as used in the carbon
      process.—TRANS.

Those who may find it necessary, or who care to prepare their own ink,
should take—chalk ink (printing) 4 parts, beeswax 10 parts, resin 7
parts, turpentine 40 parts, tallow 8 parts, Prussian blue 6 parts,
ground and mixed in a paste. The chalk printing ink should be melted
by gentle heat, then add the wax and resin in a molten condition, then
the tallow, and lastly the Prussian blue and turpentine; on account
of the inflammable nature of the latter these operations should not
be conducted at an open fire. If, after prolonged keeping, this ink
becomes tough, and does not readily leave the transfer paper when
transferring to stone, the addition of a few drops of olive oil will
restore it to a usable condition. The ink is best applied by means of
a fine, dry sponge,[R] with which it should be spread on the transfer
as evenly as possible, during which operation the print must be
protected from actinic light; on its completion the print is placed
aside to allow the turpentine to evaporate. This in a warm room will be
about ten to fifteen minutes; the print is then placed in cold water,
care being taken to remove any air-bubbles from its surface. After
remaining for about half an hour the uppermost layer will have become
sufficiently loose to allow of its removal, together with the adherent
ink not forming part of the picture, upon the application of slight
friction.

  [R] A smooth composition roller answers equally well.—TRANS.

=The Development= is readily effected by means of a small, fine wet
sponge, or a pad of cotton wool well moistened, which is passed
over the print a few times with gentle pressure; it will be found
convenient during these operations to place the transfer face upwards
upon a sheet of glass.

Judgment may be formed at this stage as to the suitability of the
negative, and also as to the correctness or otherwise of the exposure
under it of the sensitised paper; if it should have been too short the
finest lines will not be firm, but appear broken or “rotten,” as it is
technically termed. On the contrary, should the exposure have been too
long, the spaces between the lines, which should be quite free from
ink, will retain a certain amount, in attempting to remove which the
transfer will be damaged.

=Washing.=—Exposure, inking, and development being satisfactory, the
print is thoroughly washed to remove the chrome salt. Dry the transfer
by means of repeated applications of blotting-paper, and it is then
ready for transferring.

=Transferring.=—The print should retain a little moisture, but be by
no means wet. It should adhere to the warmed stone to prevent any
probability of it moving while passing through the press.

=Transfer too Adhesive.=—Should the gelatine surface, in the judgment
of the operator, appear likely to prove too adhesive, it may be further
dried before use, or placed for two minutes in a one per cent. solution
of tannin, and again dried between blotting-paper.

=Preparation of Gelatine Transfer Paper=, as used in the Imperial
Military Geographical Institute in Vienna, is described as follows
in the “Photographic Correspondence”:—A sheet of well-sized paper
is soaked in a dish of water, and when thoroughly limp is allowed to
drain, and then placed on a horizontal glass plate. All air bubbles
and superfluous moisture are removed by blotting-paper and a squeegee,
the edges of the paper are turned up to the depth of about 2 cm., and
a warm gelatine solution (1 to 30) poured upon the paper. It sets in
a few minutes, and the sheets are placed upon wire gauze to dry, this
operation usually occupying about two days. A day before using the
gelatine paper is sensitised by immersing for three minutes in a cold
bath of bichromate of potassium (1 to 15). On removal from the bath it
is allowed to drain, and the gelatine side placed upon a glass plate.
The back is dried with blotting-paper, and all air bubbles removed.
These operations and the subsequent drying must be performed in a
non-actinic light. It may occur that after these operations the sheets
when dry adhere partially or wholly to the glass plate. To prevent such
an occurrence it is well to wax the plate, as in the carbon process,
or to apply to the surface a weak solution of ox-gall.[S] When dry the
sheets are cut to the required size and printed under the negative. On
removal from the printing frame they are placed in cold water until
quite limp, removed, placed face upwards upon a glass plate, and
surface dried with blotting-paper. Should the gelatine swell too much
the sheet is placed for two minutes in a chrome-alum solution (1 to
200) and again blotted. Ordinary transfer ink, thinned with turpentine,
is now thoroughly rolled up on the inking slab by means of a leather
roller (as previously described in the instructions under Collotype);
a fine velvet roller, lightly charged with ink, is then passed over
the still moist transfer. Should the latter become dry in places it is
again passed through the water bath, and the inking is again proceeded
with. If the ink adhere to other parts than the design it is easily
removed by the application of a damp sponge or the tip of the finger.
The process of transferring to stone is as previously described. The
stone itself is prepared in the manner described for the autographic
process (see page 135). Damp the back of the transfer with water only,
and after passing through the press several times, remove the paper
from the stone; if of good quality this may be done without tearing.
The transferred impression being still easily obliterated, it is better
to let the stone stand for a few hours without gumming; this will allow
the ink to dry deeper into it. Coat the whole of the surface with a
moderately thick solution of gum, and again allow to dry. In this
condition it may remain indefinitely, but under any circumstances it is
advisable to allow it to remain a day before etching and printing. The
gum solution used should be freshly prepared, as when old it becomes
acid and acts as a mild etching medium. Remove the gum with a clean
sponge previously to printing, and while the stone is evenly damp with
gum solution the picture may be either rolled up with stiff chalk ink,
applied by means of a leather roller, or, as preferred by many, rubbed
in with a sponge containing thinned transfer ink. When the drawing
appears clean and perfect the stone is washed with a wet sponge, coated
with gum, placed aside to dry, and allowed to stand for a day. After
the removal of the gum proceed as previously described, viz., roll up
with stiffish ink, nowhere allowing the stone to become dry, and etch.
This operation must be conducted with care and judgment, or there
will be a probability of losing the finer lines of the drawing. The
best mordant to use is nitric acid, so dilute as to taste no stronger
than lemon juice, and which, placed upon the edge of the stone for a
few seconds, will show only slight effervescence. To this is added a
little gum-water, and it is then evenly and quickly spread over the
stone. After being allowed to act a few seconds, the stone is sponged
over with clean water, and is then ready for printing from.[T] There
are many practical lithographers who prefer to entirely remove the
visible image from the stone by means of turpentine before printing. A
little gum is left upon the stone, and while the latter is still moist
the drawing is removed by means of turpentine upon a piece of rag;
the latter must not be too frequently changed, or a too liberal supply
of turpentine made use of, or the drawing may be irreparably damaged.
Unless the latter be the case the picture will reappear upon applying
the roller charged with chalk ink. As may be expected, the first few
impressions are seldom so perfect as the later productions. After each
impression is removed the stone is at once slightly moistened. For this
purpose a soft, clean sponge is suitable, or damping cloth, as supplied
by dealers in printing materials. The sponge or cloth should be
thoroughly wetted, wrung as dry as possible, and in that condition will
possess the necessary dampness. In rolling it should be borne in mind
that as in Collotype a stronger grip of the roller handles and heavy
pressure with slow rolling will deposit ink upon the drawing—while, on
the other hand, light quick rolling of the drawing will tend to remove
the ink. To leave the stone without gumming after transferring is a
convenient method of rendering the transfer more receptive of the ink.
In lithographic as compared with Collotype printing the ink is reduced
to a far greater extent with varnish, while both the inking slab and
roller are charged far more heavily. The paper may be damp, or a dry,
well-sized paper may be used.

  [S] A more reliable method of imparting to the surface of the
      paper a high gloss is to squeegee it down upon a ferrotype
      plate, the surface of which requires no preparation, and the
      risk of sticking is _nil_.—TRANS.

  [T] For etching extremely delicate transfers a decoction of
      Aleppo gall with gum is to be recommended. 15 gr. of crushed
      nut galls are boiled for one hour in half a kilo of water
      and strained through a cloth. To etch the transfer add a
      few drops of this solution to a solution of gum of a syrupy
      consistency; spread over the stone with a soft sponge, and
      allow to dry.




CHAPTER XIX.

NEGATIVES FOR PHOTO-LITHOGRAPHY.


An unconditionally good negative is required for photo-lithography,
and those who have not seen one produced for the purpose by an expert
should endeavour as a first step to do so, or they will scarcely
be likely to devote the attention necessary for producing one of a
thoroughly suitable character. Not only must the lines of the copy
be represented in the negative by clear glass, and the white ground
of the original be represented by opacity, but the utmost sharpness
of definition of the finest dots and lines to the very corners of
the plate is absolutely necessary to render the negative thoroughly
serviceable. To produce such a negative a lens entirely free from
distortion, and capable of giving microscopic definition, is, of
course, a first necessity.[U]

  [U] Lenses of the rectilinear or symmetrical class are best.

=The Wet Collodion Process= is better adapted than any other for the
production of suitable negatives, possessing the necessary density
and freedom from fog or veil. The bath must work with the utmost
cleanliness, and the collodion should not be used too soon after
iodising. The developer works better when not quite fresh, and should
contain a sufficiency of acid, and the negative, after fixing, should
be subjected to a vigorous intensification.

Professor Husnik thus comments upon negatives for photo-lithography:—

“As in photo-lithography only subjects in black and white line or
stipple can be reproduced, to the entire exclusion of half-tone, the
negatives should represent the copy by clear lines and opaque spaces.
This is seldom the case except in instances where the drawings are
specially prepared, and the subjects somewhat bold and coarse. For
example, in copying a proof from a fine steel engraving the graduated,
grey, hair-lines, appear in the negative somewhat veiled, whereas the
intermediate spaces between close shading, and which are somewhat
toned in the print, are not developed actually opaque in the negative.
On this account the fine hair-lines will take longer to print in the
copying-frame than the bolder shadow lines. The latter may develop
faultlessly, while the ink may leave the hair-lines. The intermediate
spaces between close shading may not be sufficiently opaque in the
negative, consequently the print is over-exposed in these portions,
and during development remains covered with ink. Such faults must be
overcome as far as possible by shading the negative during printing in
the usual well-known manner.”

=The Colour= and condition of the original copy will greatly influence
the class of negative it is possible to obtain, and if allowable it
will be advisable

=To Bleach= old engravings or other copies, either yellow from age
or stained, by immersing them in eau-de-javelle[V] 10 cc., water
100 cc., wash in water for two hours, and finally in a weak solution
of hyposulphite of soda.

  [V] Chloride of lime     1 oz. Water  15 oz.
      Carbonate of potash  2 ”   Water   5 ”
      Mix the two solutions together, boil, and filter
      before use.

=Intensifying.=—Having developed a clear, sharp negative, wanting
only in density, it must be intensified to the utmost limit—without
fogging—first with citric acid, pyrogallic acid, and silver. This
solution may be applied either before or after fixing, preferably
the former; if this course is adopted, after washing and fixing, and
again thoroughly washing, the final intensifying operations may be
proceeded with. Opinions vary as to the actual best method to adopt,
but preference is usually given to an intensification by a salt of
mercury or lead; under any circumstances there must be a good deposit
of silver to work upon, or the necessary density cannot be obtained.
In fact, a negative too thin, submitted to mercurial combinations,
particularly the bichloride, will become more bleached and spotty, and
the after application of sulphide of potassium will not again restore
it; the deposit will assume a dark brown appearance, but the spots
arising from the mercurial salts will still be apparent. The two
mercurial salts referred to are—(1) Bichloride of mercury, corrosive
sublimate, a well-known and highly-poisonous substance used in solution
in water, and (2) iodide of mercury, which, used in intensification,
acts more evenly, though with somewhat less energy. This substance,
which is of a beautiful red colour, is insoluble in water, but is
soluble in sublimate, and also in a solution of iodide of potassium. It
is recommended for intensification, and is easily obtained by dropping
into a solution of bichloride of mercury—with agitation—a concentrated
solution of iodide of potassium until the red precipitate as first
formed is again dissolved. This yellow solution may be diluted as
required by an addition of ten times its volume of water. If, instead
of flowing the solution over the negative, a dipping bath be used,
into which the negative is steadily lowered for a few seconds, a more
uniform intensification is likely to ensue. Carefully watch the plate,
and stop the action before it goes too far, or the silver deposit will
lose strength in parts. An important gain in density may be obtained
by exposing to sun or daylight a negative which has been developed and
intensified with pyrogallic acid, fixation taking place after drying.
The negative must be thoroughly washed before exposure to light, and
with ordinary care there is little danger of fogging.

=Illumination of the Copy= should be perfectly even, a front light
being made use of, and direct sunlight if possible. The latter is
seldom admitted direct into the studio, and against outside work wind
and rain are almost fatal objections. Where much copying has to be done
it will be found an advantage, if at certain hours of the day the sun
shines direct upon the studio, to remove all blinds, screens, or other
obstructions, and so allow the rays to fall direct upon the print or
drawing to be copied.

=A Side Light=, particularly if direct sunlight, must be avoided, as
any unevenness or grain of the paper will be exaggerated and rendered
more apparent if lighted in such a manner.

=Under Exposure=, if slight, is a fault much to be preferred to an
error in the opposite direction.

=New Transfer Paper for Photo-lithography.=—In the photographic office,
Calcutta, a new method of preparing the photo-lithographic transfer
paper with arrowroot has quite recently been introduced, which, as
is said, has the advantage of being much cheaper than the method of
coating with gelatine usually adopted, and of giving results quite as
good, if not even better, than by the old proofs. Bank post paper is
coated in the usual way with two coats of the following mixture:—

  Arrowroot                 140 parts
  Bichromate of potash       70   ”
  Water                   3,500   ”

After exposure to light, the prints are coated with transfer ink in the
press as usual, the transfer ink used being composed of—

  Hard re-transfer ink (plate to stone)    100 parts
  Lithographic chalk ink                   100   ”
  Palm oil                                   7   ”

After inking in the prints are washed off with hot water, hotter than
is required for gelatine transfers. The arrowroot transfer prints are
found to go down well on the zinc without sticking, and give clear,
sharp transfers.

=Gelatine Plates= have hitherto been considered almost useless for
photo-lithography. Messrs. Mawson and Swan, however, have recently
introduced a special make, known as the “Photo-mechanical” plate, which
gives negatives of great density, and at the same time clearness in
the shadows. The makers recommend the ammonia-pyro developer, with
meta-bisulphite of potash. It will be found of considerable advantage
if, before proceeding with the development, the plate be submitted
for one minute to a bath of water 2 ounces, gallic acid 6 grains;
this, without prolonging the development, will add considerably to the
density of the resulting negative.




CHAPTER XX.

APPLICATION OF THE CARBON PROCESS TO PHOTO-LITHOGRAPHY.


=An Ingenious Process=, capable of yielding satisfactory results,
is one in which a carbon print is transferred to and developed upon
the stone direct. Such operation will present no difficulty to those
familiar with the details of the process. In the “Photographic
Archives,” vol. 17, page 193, are to be found working details, and
it is there shown that by this method it is possible to directly
transfer to stone pen and ink sketches, impressions from woodcuts,
or copper-plates, without the necessity of a photographic negative.
This process may, therefore, be available in cases where anastatic[W]
printing is not applicable.

  [W] The anastatic process consists in reproducing by zincography
      a copy of any recently printed matter. The subject for
      reproduction is moistened on the back with dilute nitric
      acid. It is then laid face downwards upon a freshly polished
      sheet of zinc and passed through the press. Printing is then
      proceeded with as in zincography. A lithographic stone may
      also be used, if, before laying down the impression, the face
      is moistened with turpentine, and allowed nearly to dry.

To those unacquainted with carbon printing it may be pointed out that
it is a most valuable process, affording great facilities for the
reproduction and reversal of negatives for Collotype. A knowledge
of the process is here presumed, as it would necessitate too wide
a digression to give an ample idea of the many useful applications
of this beautiful and permanent method of printing. Very complete
instructions will be found in Dr. Leisegang’s “Carbon Process.”[X] As
regards the application of this process to lithography, only pictures
devoid of half-tone, such as drawings in line and dot or impressions
from engravings, are suitable for reproduction by this method, if
upon clean paper (not too thick) and printed on one side only. The
sensitised tissue may be printed from the original by contact, in
the printing frame, instead of producing a negative in the camera by
contact upon a dry plate. Should it be decided to print direct from
the copy surround the edges of the same with strips of black paper or
tinfoil, half-an-inch wide, and in a weakly actinic light. So adjust
the ordinary sensitised carbon tissue that its edges are about in the
centre of the surrounding strips, care being taken that the edges of
the tissue nowhere extend beyond them.

  [X] Translated by R. B. Marston, and published by Sampson, Low
      and Co., Fleet Street, E.C. The “A B C of Pigment Printing,”
      published by the Autotype Co., Oxford Street, W.C., may also
      be recommended.

=Expose to Daylight= for a time, gauging the exposure by means of the
actinometer. Probably it will be necessary to print till the 7 shows.

=A Finely-polished Stone= is dusted and adjusted in a horizontal
position, and flowed over with cold water.

=The Exposed Tissue= is placed in cold water, and allowed to soak
till quite limp. It is then placed face downwards upon the wet stone,
covered with indiarubber sheeting, and squeegeed into close contact
with the stone; allow to remain under pressure for half-an-hour to an
hour.

=Development= is effected by pouring warm water about 100° F. over
the back of the exposed tissue. So soon as the colour exudes around
the edges of the paper backing, the latter may be removed, and the
development proceeded with by continuing to pour warm water over the
surface. Only a slight impression should remain—the lines showing the
bare stone perfectly clear and clean. Allow the stone to dry in a cool,
shady place without the application of artificial heat.

=Roll Up= with lithographic chalk ink until the surface presents a
solid black appearance, stand the stone aside for a few hours to allow
the ink to penetrate its surface, and then

=Remove the Negative= carbon print from the stone by means of a piece
of woollen cloth moistened with a thin solution of gum. This takes some
time, but it will be found that the fatty ink has penetrated where
unprotected by the carbon negative, and has formed a complete positive.

=Gum In=, etch, and proceed as in ordinary lithographic operations.
It cannot be expected that the operation, as conducted above, will
produce the finest results; the drawing will usually require a certain
amount of retouching at the hands of the lithographic artist, who will,
however, often be saved a vast amount of trouble. It is obvious that
if the proceedings, as described, be carried out, using, however, a
photographic glass positive in place of the printed impression, the
process will be found capable of giving much finer results, and the
exposure will be very materially decreased.


TRANSPOSING—BLACK AND WHITE.

A modification of the foregoing process may be utilised for the
reversal or transposition of black to white, or _vice versa_, of any
subject of which a print may be obtained in printing ink.

=An Impression= is first obtained either upon sensitised carbon tissue
or, preferably, on a thinner paper, coated and sensitised as for
photo-lithography. Such paper must not be submitted to a light of much
actinic power during or before printing, and as much ink as possible
should be used without risk of filling up the work.

=Dust Over= the impression while still wet any dense opaque colour,
applied by means of wool or camel-hair brush, carefully going over
every part and piling on as much colour as possible, after which

=Expose the Paper= bearing the print so treated to the light for a
short period, dependent upon the light and sensitiveness of the paper.
If it be a full impression, well dusted, the latitude in exposure will
be very considerable.

=Ink Up= the whole surface of the paper with lithographic transfer ink,
thinned with turpentine, and applied by means of a sponge or roller.

=Develop=, as in photo-lithography, either by means of warm or cold
water, according to the coating upon the transfer-paper. The sensitised
paper, where protected by the ink impression, has not been hardened by
the action of the light, and readily parts with the ink and colouring
matter. If the impression has been one from ordinary type it will now
show in the form of white letters on a black ground.

=Transfer to Stone=, and otherwise treat as an ordinary
photo-lithographic transfer.


ENGRAVED NEGATIVES FOR PHOTO-LITHOGRAPHY.

In certain processes for the production of photo-relief blocks many
operators prefer artificial negatives, in the production of which
photography has played no part, but which are, on the contrary, the
direct production of the artist’s hand.

=Factitious Negatives= may be produced by coating a plate with a
transparent but non-actinic coating, and by removing or erasing in a
suitable manner designs may be copied without the use of a camera or
lens. Professor Husnik and others have published different methods
whereby the artist is enabled to transfer the creations of his pencil
to zinc or stone, without resorting to the aid of the photographic
negative process, although the subsequent operations may still entitle
it to be styled photo-lithography.

The process most likely to lead to success consists of _first coating_
a glass plate with a strongly iodised collodion, _sensitising_ as
usual, well washing on both sides and drying. _To engrave_, lay the
plate upon a black cloth, and the design may be traced and engraved
upon the surface by means of etching points or needles. _Remove all_
loose particles of collodion from the plate by gentle brushing when the
drawing is completed. _Immerse the plate_ a second time in the silver
bath, and _develop_ with either pyrogallic acid or sulphate of iron
developer.

Husnik proposes to _first coat_ the plate with a solution of pure
fuchsin, and afterwards with one of gum, and then engrave as previously
indicated.[Y]

  [Y] Major Waterhouse has published the following ingenious method
      of transforming a drawing on paper into a photographic
      negative:—“A tracing, or drawing, is made in lithographic
      ink on tracing paper, using plenty of ink on the lines.
      The drawing is then placed on a board over a piece of
      blotting-paper, and brushed all over with a strong solution
      of aniline brown in water; when dry it is rubbed over with
      a tuft of cotton wool soaked in turpentine, which removes
      the ink without altering the coloured ground. The lines then
      appear clear on a dark reddish brown ground. The negatives
      thus obtained are good, but more suited for coarse than
      fine work.” It may be suggested, why not transfer the
      drawing direct to stone, and produce the necessary copies by
      lithography?—TRANS.

By either of these methods negatives of extreme density and absolute
clearness in the lines may be produced and used for obtaining
impressions in ink, the transfer of which to stone presents no
difficulty.

It remains to be added that there are several methods of producing
grained negatives for photo-lithography in half-tone, and therefrom a
transfer for stone, and so obtaining impressions at a much greater rate
than is possible from a Collotype plate. They may each produce results
with a certain amount of success; but even those from the best methods
indicated cannot be compared with Collotype. The too obtrusive grain of
the half-tone pictures so produced destroys much of the finer details,
and it is to be regretted that all such processes leave so much to be
desired.




APPENDIX.

THE STEAM COLLOTYPE MACHINE.


The earliest steam machines for Collotype printing were made by Faber
& Co., of Offenbach; they were, however, so complicated and delicate
in construction that other machines have entirely supplanted them.
The three principal varieties are those of Alauzet & Co., of Paris;
Koch, of Leipzig; and Schmiers, Werner & Stein, each of which may
be considered entirely successful; they possess features of great
similarity, differing not in principle, but only in details of
construction. Contrasting the work of the machine with that of the
press, the printing is much more rapid, and the prints more uniform
and regular, while the “life” of the plate is greatly lengthened; one
capable of yielding 250 impressions on the scraper press would, in
all probability, give 1,000 on the machine—a fact easily accounted
for when it is considered that the one is produced by a scraping
pressure while the other is made by the rotation of a cylinder. As
will be seen by the illustrations, the machines bear a considerable
resemblance to those used in lithography—they may, in fact, be used
for lithographic printing—with very greatly increased inking power.
The machines are so constructed that the plate may be inked once,
twice, or three times, each inking giving more vigour, but, of course,
a corresponding decrease in the number of impressions yielded; the
output may be relatively estimated at 1,500, 1,000, and 800 per day. It
is, of course, an impossibility to teach machine printing by means of
instructions such as may be conveyed in a work like the present, and
the following remarks are added more with a view of giving a general
idea of the nature of the necessary operations than with any idea of
making the reader a competent machine minder.

=The Preparation of the Plate= for the machine is identical with its
preparation for the hand-press, but greater uniformity, both in the
negative, exposure, and etching, are demanded than by the hand-press.
For the latter considerable latitude is permissible, as the intelligent
printer may, by varying his rollers, his rate of rolling and other
little dodges, produce perfect impressions from plates which would,
under the entirely mechanical action of the machine, fail lamentably.

=Adjustment of the Rollers= is so effected that they are lifted about
2 mm. when passing over the inking slabs and the printing plate; if a
greater lift is necessary to bring them upon the printing surface marks
will be produced upon the plate, and if arranged for a less lift they
will probably skid over the plate, damaging the printing surface. They
should also be adjusted perfectly parallel with the surface of the
inking tables, or one side only may come in contact with the work.

=Fixing the Plate= to the bed of the machine is effected in several
ways, but usually with small clips, as described for the hand-press.
All adhering gelatine, etc., must be removed from the plate, and a thin
sheet of white paper inserted between it and the bed of the press. The
faces of the metal clips must be protected with strips of leather,
cork, or some such elastic bodies, otherwise the pressure exerted would
cause the glass to fly. A straight edge is placed across the machine,
and the bed lowered by means of inclined planes attached to suitable
gearing until the surface of the plate is well below the circumference
of the cylinder, and from this position it is brought up to its proper
level, raising each side equally, that the pressure may be perfectly
uniform.

=Packing the Cylinder.=—The cylinders are so constructed that the iron
surface does not come in actual contact with the printing paper. In
fact, there is a deficiency between the actual and necessary diameter
of the cylinder of a few mm., sometimes as much as 7 mm. This is
compensated for by the addition to its surface of “packing,” which
gives a more elastic pressure than the unyielding surface of iron. This
packing is not applied to the entire surface of the cylinder, but is so
devised that it exerts pressure upon the surface of the picture only.
A sheet of smooth four-ply cardboard is attached to the cylinder by
means of thin glue, this first sheet usually exceeding the size of the
picture. To this is attached a second piece, cut of the exact size of
the image, and attached by means of the glue, forming a raised block in
exact register with the position of the picture on the printing plate;
this is covered with a thickness or two of fine blotting-paper, and
over the whole the sheeting of the cylinder is tightly stretched in
the usual well-known manner. It is self-evident that the circumference
of the cylinder must traverse at exactly the same speed as the bed of
the machine, or there will be a horizontal rubbing or friction between
the surface of the printing paper and that of the printing layer,
which will result in impressions lacking in sharpness, and ultimate
destruction of the plate.

=Masking the Prints= for the production of white margins is usually
performed by one of two methods, each having advantages and
disadvantages which should be carefully considered before adopting
either; both are in practical use. In one is used a light rectangular
iron framework or “frisket,” conforming to the size of the cylinder,
to which it is attached by hinges. This framework is opened and closed
automatically, remaining open during the period the cylinder is resting
and the inking is taking place. At this point the “layer-on” inserts
the paper, it is seized by the grippers, and the masking frame closes
down into suitable grooves in the circumference of the cylinder, such
grooves being useful to prevent any lateral movement of the frame. To
the latter are attached four movable strips of thin zinc, which may be
adjusted by means of set screws to form an opening of any desired size.
The printing paper being inserted in the grippers, the frame closes,
holding the paper upon the cylinder, the strips of zinc at the same
time protecting the edges of the paper from immediate contact with the
printing layer, the cylinder revolves, and the printing is effected. In
large sizes the zinc strips are necessarily of such strength that the
edges would cut and damage the printing layer; it is therefore usual to
adjust the strips to within about 5 mm. of the edges of the picture,
and by attaching strips of varnished tissue paper to the zinc, reducing
the aperture to the size of the picture in hand. In large sizes—where
thin paper is used, or where narrow margins are desired—this system of
masking is best, as the whole of the operation is entirely automatic.
The layer-on may devote the whole of his attention to removing
impressions and inserting fresh paper.

=Another System= of masking frequently made use of is one in which an
aperture of suitable size is cut in a piece of cardboard, such aperture
being, say, 2 mm. larger than the print. The portion removed is
reduced in size by 2 mm. all round, leaving it exactly the size of the
impression desired. This piece is utilised for packing by attaching to
the cylinder as previously described. The cardboard mask, presenting
the exact appearance of a sunk mount, is affixed by means of a bar to
the cylinder, and when folded down upon the latter, the “cut out” used
as packing exactly occupies the centre of the mask, leaving a marginal
space all round of 2 mm. Before printing, the mask must be varnished
with negative varnish, bitumen in benzol, or otherwise waterproofed, to
prevent adhesion to the print layer. The mask has to be turned back by
hand at the insertion of each sheet—a considerable disadvantage when
compared with the automatic frame. On the other hand, its advantages
are simplicity of preparation, and the possibility it allows of masking
and printing several irregularly-disposed pictures on one sheet.

=Damping the Plate.=—The use of the cylinder pressure has further
advantages than merely prolonging the life of the plate—the operation
of damping is much less needed than on the hand-press. The printing
paper does not come in contact with the plate before the instant of
printing or remain upon it after the operation, but is held to the
cylinder by the grippers and mask, and so carried over the inked
plate, consequently little opportunity is afforded for absorption of
the etching fluid. With chalk paper and a new plate damping may be
necessary every twenty-five impressions, but as the plate becomes older
fifty or even one hundred may be printed between the etchings. On plain
paper of hard surface much longer numbers may be expected.

=The Inking Tables=, two in number, are provided one at either end of
the machine, necessitating two sets of inking rollers—one of leather
for applying the thick ink, and another of composition for supplying
the “half-tone,” the latter set requiring such light application
to the plate that no riders are required. There are also the usual
distributing rollers, to which the ink is generally supplied by the
printer as may be necessary, the quantity being so small that no
actually satisfactory automatic duct has yet been devised. A proper
adjustment of the consistency of the two inks to the requirements of
the plate in hand is a matter of considerable delicacy, for should
the ink supplied to the leather rollers be too thin it is immediately
removed from the printing plate by the composition rollers; these
again transfer it to the table devoted to the thin ink, and a general
“wash up” is the necessary result. The ink first supplied to the
leather rollers should be as stiff as possible, afterwards reducing as
experience may dictate, while to the composition or tone rollers merely
coloured varnish, or even varnish alone, is applied, as the latter
often remove enough colour from the printing plate to sufficiently
tint the varnish applied to their surface. The leather rollers should
be cleaned daily by scraping, and the composition set washed, unless
the weather be very cold or damp. In such cases they may be allowed to
stand under ink, as they will in that condition be less susceptible to
atmospheric changes.

=Double Printing= is sometimes resorted to for work of a high class,
and when negatives too thin to produce good results otherwise are
unavoidably used, such work is usually printed on chalk paper and
without masking. The printing plate is usually inked up twice and an
impression taken; without removing the impression from the cylinder the
plate is again twice inked and a second impression pulled on the same
piece of paper, the two images being exactly super-imposed. The great
gain in contrast will be understood when it is considered that while
the high lights of the picture gain absolutely nothing, the strength of
the shadows is exactly doubled. The results produced in this way are
simply astonishing when contrasted with silver prints from the same
negatives.




ADVERTISEMENTS.


  HUGO KOCH,
  LEIPZIG-CONNEWITZ, GERMANY,

  MANUFACTURER OF
  COLLOTYPE STEAM PRESSES.

  Awarded First Prizes at all Exhibitions where our Presses have
  competed.

  —> World’s Exhibition, Antwerp, 1885, Diploma of Honour. <—

  [Illustration]

  THE
  KOCH COLLOTYPE STEAM PRESS IS THE BEST IN THE MARKET
  MADE IN FOUR SIZES.
  AUTOMATIC FEED BOARD, FRISKET, AND INK DUCT.

  If desired, the press can be arranged also for litho or type printing

      *.* That these machines have been adopted, _to the exclusion
          of all others_, in establishments of such repute as those
          of Albert, of Munich, and the “Phototypisches Institute”
          of Berlin, are facts of the greatest significance.

  PRICES AND PARTICULARS ON APPLICATION TO
  HUGO KOCH, Leipzig-Connewitz, GERMANY,
  OR
  BEESLEY & CO., YORK PASSAGE, BIRMINGHAM.




  SCHMIERS, WERNER AND STEIN,
  MANUFACTURERS OF
  PRINTING MACHINERY

  [Illustration]

  OUR COLLOTYPE MACHINES have now been introduced for upwards of twelve
  years, during which period they have been adopted by the most renowned
  Collotype establishments in all countries.

  They are manufactured in four sizes, with all recent improvements,
  and may be ordered either with or without masking frames, the utmost
  satisfaction being guaranteed.

  They may be utilised for Lithographic Printing.

      Litho Steam Machines in Five sizes.
      Bronzing Machines in Two sizes.

  Further information in reply to all questions on application to

  SCHMIERS, WERNER & STEIN,
  DÖSENER WEG, LEIPZIG.




  _ESTABLISHED 1823._

  BERGER & WIRTH,
  LEIPZIG, GERMANY,

  Ink Manufacturers.

  SPECIALITIES—

  COLLOTYPE INKS
  In all Shades.

  PRICES AND SAMPLES
  _FORWARDED UPON APPLICATION_.




  [Illustration]

  THE MAWSON
  “Photo-Mechanical” Plates
  ARE SPECIALLY MADE FOR
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          PHOTO-ETCHERS & COPYING.

         *       *       *       *       *

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         *       *       *       *       *

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  GELATINE.

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  Sold Retail by all Dealers in Photographic Materials. Wholesale by the
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  STRIPPING FILMS

  [Illustration]

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  AN INTRODUCTION TO
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  THE INDISPENSABLE HANDBOOK
  TO
  The Optical Lantern:
  A COMPLETE CYCLOPÆDIA ON THE SUBJECT OF
  OPTICAL LANTERNS, SLIDES, AND ACCESSORY APPARATUS.

         COMPILED BY         EDITED BY
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  CONTENTS.

  SECTION I.

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  400 PAGES. NUMEROUS ILLUSTRATIONS.
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  AND ALL BOOKSELLERS AND BOOKSTALLS

  Editorial and Advertisement Offices: VICAR LANE, COVENTRY.




Transcriber’s Note:

Punctuation has been standardised. Spelling and hyphenation have been
retained as they appear in the original publication except as follows:

  Page 26
  two to three in cm. width over _changed to_
  two to three cm. in width over

  Page 30
  on the mercury and quntiaty of air _changed to_
  on the mercury and quantity of air

  Page 38
  may be also used in photo-zylography _changed to_
  may be also used in photo-xylography

  Page 97
  with a mat surface or varnished _changed to_
  with a matt surface or varnished

  Page 103
  The Artotype Co. take _changed to_
  The Artotype Co. takes

  Page 107
  If this fail to produce sufficient _changed to_
  If this fails to produce sufficient

  Page 122
  we owe the orgination of this _changed to_
  we owe the origination of this

  develope the invisible image _changed to_
  develop the invisible image

  Page 126
  60° Reamur _changed to_
  60° Réamur

  Advertisements
  DÖESENER WEG, LEIPSIG. _changed to_
  DÖSENER WEG, LEIPZIG.

  LEIPSIC, GERMANY, _changed to_
  LEIPZIG, GERMANY,

  INKS, ROLLERS, CHEMICAL S _changed to_
  INKS, ROLLERS, CHEMICALS

  Schweinfurt a/ Maine _changed to_
  Schweinfurt a/ Main

  A. & M. ZMIMERMANN _changed to_
  A. & M. ZIMMERMANN





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