9° Beaumé) at a temperature of 15° C. Etch galvanically in this bath
by placing in it a clean |104| copper dish. The plate prepared for
etching as per page 84, is rubbed bright at the four corners and four
S-shaped narrow strips of sheet copper are so fastened to the bright
zinc that the S-shaped end rises about three millimetres over the
picture. Then place the plate face downward for three minutes into the
bath, above the copper plate, which is electrically connected with the
zinc by brass strips, so that instantly a strong galvanic current is
set up. The etchings are found to be very satisfactory and interesting.
In three periods (nine minutes) a beautiful preliminary etching is
obtained with rather perpendicular faces.
I cannot recommend etching by shaking, as the sediment causes rupture
of the finest lines.
PROCESS FOR HIGH ETCHING IN RELIEF.
Experienced etchers can also apply their art to the reproduction of
drawings by means of the printer’s press, in the following manner:
A plate, ready for etching and free from grease, is cleaned with weakly
acidified water, the remaining water drawn off with a blotter, and the
plate gently heated. By means of a pad a fine paste of graphite is
rubbed upon the surface; it is then moderately heated and a very thin
gauze-like layer of warm white wax is applied to the graphite surface.
After cooling the plate, spread upon it a coat consisting of the finest
orange-colored chrome yellow (rubbed to a fine dough with water and
gum). In this ground layer we can erase as for deep etching.
Brush the finished surface with writing ink dissolved in benzine (using
a fine wide brush). The plate should be warm. Take a pad made of
cotton, dip it into water and work over the surface in small circles
until the image has become well developed. From this point we can
continue according to the usual method.
J. O. MÖRCH.
THE RUNNING OF A WORKSHOP.
The great competition demands of every chemigraphical business a
ready, productive organization, which is also attentive to the rules
of economy. In following out the latter it is advisable to aim at
a division of labor. By giving to the single workmen more practice
in each particular manipulation, the quality of the work is also
promoted. To secure a lucrative trade, we need the following helpers:
1. A foreman thoroughly acquainted with the whole process. 2. A
photographic assistant, who is skilled especially in straight line
|105| reproduction, and who aids in the copying of negatives. 3. A
carpenter, at the same time polisher of the zinc and finisher of the
plates, who will also assist at other things in general. 4. A first
manipulator, who understands blacking of the plates and the examination
of the same throughout the whole process. 5. A man to form the etching
varnish on the plates. 6. A man to scrape off. 7. A man to etch. 8.
One to wash plates and to make himself generally useful. With the aid
of such a staff it is possible to produce 2000 square centimetres of
etching daily, and by the addition of a ninth assistant the capacity
can be raised to 3000 square centimetres.
A first manipulator can be trained in three months, a carpenter in the
same time, and the others in four to six weeks.
The head of the establishment will, of course, be doubly busy during
these first months. Upon his abilities depends the success of the whole.
I think it is inadvisable to introduce etching into all the printing
establishments, as production on a small scale is far more expensive
and less satisfactory. But it _is_ advisable to add to the chemigraphy
a small lithographical laboratory.—J. O. MORCH.
SOME WRINKLES AND DODGES.
As I had to stumble through to success like many others, I gladly give
a few little items of practice which may speed the work of others. I
like this for a sensitizing solution:
Bichromate of Potash in powder 1 ounce.
Water 15 ounces.
Alcohol (950) 4 ounces.
Liquor Ammonia 1 ounce.
After I have sensitized the gelatine transfer paper I increase the
surface quality by laying it upon a glass plate which has been heated
_very slightly indeed_ with vaseline. I use a squeegee to secure close
contact and then stand it up to dry, say over night. A slight start at
one corner with a knife point will cause the paper to leave the glass
readily.
It pays always to get the best material. Nothing is worse than a bad
quality of zinc. I use No. 10. A strong, well-made clotheswringer will
answer for a time, for making transfers, when a lithographic press is
not convenient. The pressure should be uniform.
Learn to be systematic until you are familiar with all the details
of the work. It might be well for you to make a numbered list of the
necessary operations |106| and paste it up where you can see it and
refer to it handily. Accustom yourself to having a place for everything
and everything in its place. I have seen many an etching lost by
disregard of this rule.—C. W. ROCHE.
CARBON PRINTING.
In Chapters III. and IV. on engraving on copper, the resist and relief
are made by what is called in photographic nomenclature the carbon
process—that is, printing in gelatine to which has been added a
suitable pigment. This pigmented gelatine, spread upon paper and dried,
is known in commerce as carbon tissue, and is sold of various colors
and degrees of density as regards the quantity of pigment incorporated
with the gelatine. For our purpose that tissue containing the minimum
quantity of pigment is the best (this only applies to the resist or
relief on the copper, not to the transparency necessary for printing
the resist from; in this case what is known as transparency tissue must
be used, and that is made with the maximum quantity of pigment (India
ink) incorporated with the gelatine), but as the subject of making
transparencies in carbon has already been treated of, the present notes
will be confined entirely to developing carbon prints upon copper for
resists (Chapter III. for reliefs Chapter IV.).
The carbon tissue of commerce is not sold in a sensitive condition;
therefore, the first care will be to render it sensitive to the action
of light, which is done by immersion in a solution of bichromates of
potash and ammonia.
First of all dissolve in eighty ounces of water one and a half ounces
of bichromate of ammonia, and one ounce of bichromate of potassium, and
filter. Then cut the carbon tissue into suitable sized pieces—_i. e._,
pieces a little larger than the subject on the transparency or negative
to be used, and a little smaller than the copper plate upon which it
is intended to develop the carbon print; next select a sufficient
number of glass plates quite free from scratches a little larger
than the pieces of tissue, now clean these glass plates carefully by
polishing with clean linen or silk cloth free from lint, then dust over
with French chalk and again well polish; then coat with thin plain
collodion, and when the film is well set place the collodionized plate
in clean cold water until the greasy appearance that shows on the first
immersion in the water has disappeared.
Place the filtered bichromate solution in a clean dish, then immerse
the pieces of tissue, one at a time, taking care that no air bells are
allowed to |107| remain upon the surface; if any form, remove them
by bursting them with the fingers. After the tissue has been in the
solution for three minutes, take one of the collodionized and washed
plates from the water and remove one of the pieces of tissue from the
bichromate bath, place the two face to face, lowering the tissue gently
down upon the collodion film, then place the glass plate upon a bench,
lay a piece of Macintosh cloth (larger than the plate) over the tissue,
and with a squeegee gently scrape along the Macintosh; this will bring
the carbon tissue into contact with the collodion film, and also expel
superfluous bichromate solution, but care must be taken not to remove
too much of the bichromate else the tissue will be insensitive and
print hard. The plate is now placed upon a rack, and all the remaining
pieces being done in the same way are also placed upon the rack.
The tissue being thus squeegeed into optical contact (the squeegee is
made with a strip of soft rubber fixed between two pieces of wood) with
the collodionized glass, it must be dried in the dark room in a current
of warm air, not higher than 60° F., else the pigmented gelatine will
melt and be useless (bye the bye, the bichromate solution in hot
weather should be iced so as to keep the temperature below 50° F.).
When the tissue is dry it is stripped from the glass and stored in a
tin tube, and care must be taken to keep it away from the light, as
if the tissue be once exposed to the light even for a short time, the
action will go on in the dark.
In treating of the transparencies, it is mentioned that the subject on
the transparency or negative is marked, this being necessary to form
what is called a safe edge to the carbon print. If such a safe edge be
not provided, the carbon print will not adhere to the copper during
development; therefore, the extreme edges of the tissue must be guarded
from the light during the exposure in the printing frame.
The exposure to light under the negative or transparency must be timed
by means of an actinometer, which may be improvised by dividing a strip
of tracing paper into ten spaces, and numbering these spaces so:
─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬──────
│ │ │ │ │ │ │ │ │
1 │ 2 │ 3 │ 4 │ 5 │ 6 │ 7 │ 8 │ 9 │ 10
│ │ │ │ │ │ │ │ │
─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴──────
Write the figures with good black ink and then cut other pieces of
white tracing paper into strips of the same width. |108|
Now lay the piece of tracing paper with the numbers on it, upon a
piece of glass 4-1/4 × 3-1/4 inches, and fix it in the centre, then
place thicknesses of tracing paper over this so that space 2 has three
thicknesses of tracing paper, space 3 five thicknesses, space 4 seven
thicknesses, space 5 eight, space 6 nine, and so on up to 10. Now if a
piece of ordinary sensitive albumen paper is put into a frame behind
this screen, it will form an actinometer, and when, after exposure to
light the figure 5 is just visible, five tints are registered.
This actinometer will with practice enable the operator to judge when
the carbon tissue has been exposed sufficiently long; the only guide
that can be given, is to err on the side of overexposure rather than
underexpose.
The carbon tissue being exposed, it is removed from the frame, and
placed in clean cold water; then as soon as it begins to uncurl itself,
the copper plate is placed in the water, and the two are brought into
contact, the tissue adjusted in position upon the copper, then removed
from the water, and a squeegee applied vigorously to the back of the
tissue, applying the squeegee first one way and then the other.
Now allow to stand a few minutes, then immerse it in water at a
temperature of 90° or 95° F., and in a few minutes the pigmented
gelatine will begin to ooze from under the paper backing, which may now
be stripped off and thrown away. The copper plate may now be raised
and gently laved with the hot water, or it may be allowed to remain
until the whole of the soluble gelatine is dissolved away, leaving the
picture upon the copper plate, which is rinsed in cold water and dried.
For the purpose of copper plate work, the image must be thoroughly
well exposed, every detail being impressed, else it will be impossible
to get a good photogravure; therefore, until the operator thoroughly
understands the use of the actinometer it will be as well to make a few
prints upon a piece of opal glass.
Carbon tissue does not keep in a sensitive condition more than a month,
under the most favorable conditions, the general time perhaps being a
week. The first sign of deterioration is generally shown when trying to
mount upon the copper, after soaking in cold water, the tissue refusing
to adhere after the application of the squeegee. The best way to test
the sensitive tissue is to take a small piece and immerse it in cold
water for a minute, then put it into water at 95°, and, if the coating
dissolves off the paper the tissue is all right; if it does not, it is
useless. Tissue will generally be found at its best about |109| three
days after sensitizing, and will gain rapidly in sensitiveness daily
afterward.
Carbon tissue can be made at home, the following being the formula:
Gelatine (soft) 10 ounces.
Sugar 4 ounces.
Water 30 ounces.
Dissolve the gelatine at as low a temperature as possible, then add
the sugar and churn thoroughly; then add sixty grains of India-ink,
previously dissolved in a little water, again churn, then strain
through muslin into a dish (which dish is placed in another containing
hot water). Now take two sheets of paper, grasp one end tightly and
drag them rapidly through the tissue compound, and directly they are
lifted clear of the solution let an assistant grasp the bottom and you
dropping the top, will reverse the sheets and keep the gelatine on the
surface of the paper; when the gelatine has set, divide the two sheets
and hang up to dry; when dry the subsequent proceedings are the same as
for commercial tissue.
COLAS’S BLACK PROCESS.
This process will often be found useful to reproduce a drawing on
yellow tracing-paper, so as to give a more suitable copy to photograph
from.
Coat with a fine sponge a hard, well-sized paper, with
Water 300 parts.
Gelatine 10 parts.
Perchloride of Iron (dry) 20 parts.
Tartaric Acid 10 parts.
Persulphate of Zinc 10 parts.
and dry in a dark-room.
When dry, expose under the tracing until the greenish-yellow tint of
the paper has disappeared, except where covered by the opaque lines.
Development is effected in a bath made by dissolving 20 parts of gallic
acid in 200 parts of alcohol and 1000 parts of water; then wash in
plenty of clean water.
MORDANTS FOR ETCHING.
I. MORDANTS FOR STEEL.—Nitric acid forms the basis of most fluids for
etching steel as well as for other metals. Acetic acid and alcohol are
sometimes added, and some formulæ contain nitrate of silver, corrosive
sublimate, salts of |110| copper, etc. Iodine is also a most efficient
mordant for steel, and Mr. Fox-Talbot used the chlorides of iron and
platinum for etching his plates through the coating of bichromated
gelatine.
_Plain Acid Mordant.—(Kruger.)_
First biting:
Muriatic or Nitric Acid 1 part.
Water 8 parts.
Stronger:
Acid 1 part.
Water 4 parts.
Deepest:
Equal parts acid and water.
_Kruger._—Chromic acid, diluted according to the effect to be produced.
This also serves for zinc, copper, and brass, and bites with great ease
and certainty, making a good vertical cut.
_Ed. Turrell._
Glacial Acetic Acid 4 parts.
Absolute Alcohol 1 part.
Nitric Acid (specific gravity, 1.28) 1 part.
The acetic acid and alcohol are mixed and allowed to stand for half an
hour, then the nitric acid is added very gradually. This mordant is
applied from one to fifteen minutes, according to the strength desired,
and may be strengthened by adding nitric acid.
_Etching Solution with Alcohol._
Alcohol seems to be added with the object of softening the action in
the first biting, and of making the mordant bite at once. For etching
Niepce de St. Victor’s asphaltum plates, M. Lemaitre used, for the
first biting:
Nitric acid, at 36° 1 part.
Distilled Water 8 parts.
Alcohol, at 36° 2 parts.
And finished off with nitric acid and water, without alcohol.
_Etching Solution with Nitrate of Silver._
Alcohol 6 parts.
Distilled Water 9 parts.
Pure Nitric Acid 16.6 parts.
Nitrate of Silver 0.83 parts. |111|
The liquid improves by keeping. Before beginning, wash the plate for a
few seconds with dilute nitric acid (at four per cent.), then apply
the above mordant for about three minutes, and wash off with distilled
water containing six per cent. of alcohol. Repeat the biting as often
as may be necessary, well washing between each operation.
_Deleschamps.—Glyphogen._
Acetate of Silver 8 parts.
Rectified Spirits 500 parts.
Distilled Water 500 parts.
Pure Nitric Acid 260 parts.
Nitric Ether 64 parts.
Oxalic Acid 4 parts.
This is recommended as being free from the defects of many of the other
mordants, and as giving a clean vertical bite.
Several formulæ contain salts of copper.
_Roret._
Nitric Acid 62 parts.
Distilled Water 125 parts.
Alcohol 187 parts.
Nitrate of Copper 8 parts.
Iodine is recommended as a very efficient mordant for steel, being free
from the inconveniences caused by the disengagement of gas, as when
biting with nitric acid. Messrs. Schwarz and Boehme give the following:
Iodine 2 parts.
Iodide of Potassium 5 parts.
Water 40 parts.
This may be further diluted up to 40 parts more water, for etching the
finest lines. It gives good deep lines, sharp, and with clear edges
even, for the finest and closely ruled lines have no tendency to run
one into the other.
The following resembles the etching fluids for copper, commonly known
as “Dutch mordant.”
_Cooley._
Hydrochloric Acid 5 parts.
Water 95 parts.
Mix and add:
Chlorate of Potash 1 part.
Water 50 parts. |112|
_Cooley._—For electric etching with the battery, a solution of common
salt is used.
II. MORDANTS FOR COPPER.—The most useful mordants for copper are nitric
and nitrous acids, more or less diluted with water. Latterly, however,
a mixture of chlorate of potash and hydrochloric acid, known as the
“Dutch mordant,” has come more into use. For some purposes, perchloride
of iron in solution is a useful mordant, particularly in photographic
work with gelatine films. These two latter mordants bite more quietly
than the acids, so that the lines are not so much enlarged, and
there is not the same risk of close lines running together and other
inconveniences caused by the evolution of bubbles of gas.
_Acid Mordants.—(Lalanne.)_
Nitric Acid, at 40° 1 part.
Water 1 part.
With a little old etching solution added, or pieces of scrap copper.
_Malaret._
Nitric or Sulphuric Acid 1 part.
Saturated Solution of Bichromate of Potash 2 parts.
Water 5 parts.
Fizeau used for daguerrotype etching a mordant composed of nitric,
nitrous, and hydrochloric acids.
_Dutch Mordant._
Fuming Muriatic Acid (specific gravity, 1.190) 10 parts.
Water 70 parts.
To this add a boiling solution of
Chlorate of Potash 2 parts.
Water 20 parts.
This may be diluted with from 100 to 400 parts of water as required.
Perchloride of iron, more or less diluted in water, is, according
to Hamerton, an excellent mordant. It bites deep and clear, without
enlarging the line much, and there is no ebullition, as with nitric
acid. It is particularly useful in photographic etching through
gelatine, as the latter is insoluble in it.
In most cases the mordant is flowed over the plate, or kept moving
on it in the same way as a photographic developer. Such mordants are
generally used for finishing off and deepening the light tints, and are
called _eau fortis à couler or à passer_. The following formulæ are
given: |113|
_Roret.—(Abraham Rosse’s.)_
Strong White or Distilled Vinegar 3 litres.
Sal Ammoniac 180 grammes.
Common Salt 180 grammes.
Pure Verdigris 120 grammes.
A little oxalic acid is sometimes added. The solids are ground up, and
boiled in the vinegar. Acetic acid at 3°, or pyroligneous acid, may be
used in place of vinegar, and, if too strong, more vinegar should be
added.
The following, used by Callot and Piranesi, is similar and prepared in
the same way:
Strong Vinegar 8 parts.
Verdigris 4 parts.
Sal Ammoniac 4 parts.
Salt 4 parts.
Alum 1 part.
Water 16 parts.
For relief etching use only 10 parts of water.
_Relief Etching._
For etching copper in relief, the following glyphogen is recommended by
Deleschamps:
Nitrous Acid, at 30° 2 ounces.
Acetate of Silver 6 drachms.
Hydrated Nitric Ether 16 ounces.
The nitric ether is prepared by mixing two ounces each of nitric acid
and alcohol, and, when the reaction commences, stopping it by adding
eight ounces of distilled water.
_Tint Etching._
Flour of sulphur mixed with oil forms a good composition for etching
tints. It can be applied with a brush. For a flat tint, Hamerton says
“Oil the plate liberally with olive oil, and blow flour of sulphur upon
this.” The sulphur, if allowed to remain on the plate, will produce a
flat tint, more or less deep in proportion to the time it remains.
Roret gives the following formula for tint etching:
Bay Salt 2 parts.
Sal Ammoniac 1 parts.
Verdigris 1 part.
These are pounded together, and the mixture kept in a bottle. |114|
When required for use, grind up a little in a glass with some syrup of
old honey, so as to make a mixture which flows readily. It may be used
with a brush like a color. It is used after the bitings of aquatint
plates with acid, to give finish and vary the tints.
_Fielding (for aquatint)._
Nitrous Acid 1 part.
Water 5 parts.
For the strongest touches, nitrous acid and water, equal parts, applied
with a feather or brush. No. 19 may also be used for this purpose,
either with or without a little gum.
_Hamman._—Dilute nitric acid at 12° (sp. gr. 1.09), mixed with:
Distilled Water 12 parts.
Alcohol 3 parts.
This is said to give a grain in biting, so that the ordinary grained
ground may be dispensed with.
_Electric Etching._
It has frequently been proposed to etch by means of electricity, and in
some cases it may be an advantage to do so.
The copper plate to be engraved is attached to the positive pole of
a suitable battery and placed as anode in a solution of sulphate of
copper, or in water acidulated with sulphuric acid.
In suitable cases, different degrees of depth may be given, putting
parts of the anode and cathode nearer together or further apart.
Grove etched daguerrotype plates with a single pair of Grove or Bunsen
cells, by inserting the plate to be etched, and a platinum plate of the
same size, in a wooden frame having two grooves a quarter of an inch
apart.
The daguerrotype having been attached to the battery as anode, and the
platinum plates as cathode, the frame is immersed in a suitable vessel
filled with
Hydrochloric Acid 2 parts.
Distilled Water 1 part.
Contact is made for about half a minute, after which the plate is
removed from the acid, washed thoroughly with distilled water, then
placed in a solution of hyposulphite of soda or ammonia, and the
deposit removed from the surface |115| with gentle rubbing with
cotton. It is again rinsed with distilled water and dried.
MORDANTS FOR ZINC.
The comparative cheapness of zinc would give it an advantage over
copper or steel for engraving or etching with the graver or point,
but it does not seem to be recommended for these purposes. It is
hard to cut with the graver, and, though it bites easily, it is not
suitable for fine work. Another defect is that it will not stand a
long impression; but this may be overcome by surfacing the plate with
copper. The principal uses of this metal for printing purposes are for
surface printing or zincography in the same manner as lithography, and
for the process of biting in relief, and zinco-typography or Gillotage,
now so largely employed as a substitute for wood blocks. It can also
be engraved very delicately in the same style as engraving is done on
stone, through a coating of gum.
The etching fluids for zinc are of two entirely different kinds:
first, mixtures of gum and weak acids used for preparing plates for
zincographic printing in the lithographic press, or for preliminary
inking preparatory to being bitten in relief by the Gillotage process;
and secondly, mineral acid, more or less dilute, used for biting in
relief and ordinary etching.
_Zincographic Etching._
This kind of etching is more of a preparation of the plate for printing
than engraving or biting, the object being merely to fill up the pores
of the metal with gum, and prevent it receiving printers’ ink from the
roller elsewhere than on the lines of the drawing.
The solution most commonly employed for this purpose is a mixture
of gum and decoction of nut-galls, in use at the Ordnance Survey
Office, Southampton, and given by Sir Henry James in his work on
_Photo-zincography_. It is prepared as follows: Four ounces of Aleppo
galls are bruised and steeped in three quarts of cold water for
twenty-four hours; the water and galls are then boiled up together, and
the decoction strained. The gum-water should be about the consistency
of cream. One quart of the decoction of galls is added to three quarts
of the gum-water and to the mixture are added about three ounces of
phosphoric acid, which is prepared by placing sticks of phosphorus in a
loosely corked bottle of water, so that the ends of the sticks may be
uncovered. The oxidation of the phosphorus produces phosphoric acid,
which dissolves as fast as it is formed. |116|
The etching solution should only just mark a piece of plain zinc.
In Richmond’s _Grammar of Lithography_ the following modifications of
this formula are given:
Decoction of Nutgalls 3/4 pint.
Gum Water as thick as Cream 1/4 pint.
Phosphoric Acid Solution 3 drachms.
Boil one and a quarter ounces of bruised nutgalls in one and a quarter
pounds of water till reduced to one-third, strain, and add two drachms
of nitric acid and four drops of acetic acid.
Richmond recommends, however, the use of a simple decoction of galls
without acid, and gumming in after etching.
Scamoni has the following, by Garnier: Boil about one and a half ounces
of bruised gall-nuts in a pint of water till reduced to one-third,
filter, and add two drops of nitric acid, and three or four drops of
muriatic acid. For very fine work this may be weakened with water. It
is applied for about a minute, then washed off, and the plate gummed.
_Zinco-typographic Etching._
In biting zinc plates in relief, the acid generally used is nitric of
different degrees of strength, according to the nature and state of the
work.
After the transfer is made, the plate is etched with one of the
foregoing preparations, then inked in and dusted with finely powdered
resin, which adheres only to the lines. This procedure is followed
after every biting, the plate being warmed to melt the resin and inky
coating, so that it may run down between the lines and protect them
from the undercutting action of the acid.
Kruger, in his _Die Zinkogravure_, recommends for the first relief
etching, nitric acid 30 to 40 drops to 100 grammes of water, applied
for five minutes. For each subsequent etching, 8 to 10 drops of acid
are added for each 100 grammes of water, and the time is increased,
from five to fifteen minutes. For the final etching of the broad lights
he uses:
Muriatic Acid 4 parts.
Nitric acid 1 part.
Water 16 parts.
To soften down the ridges between the lines the plate is inked and
dusted as before, and etched with dilute nitric acid at five per cent.,
applied for a |117| minute, and the inking, dusting, and etching
repeated as often as may be necessary.
THE DIFFERENCE.
Finally, in this department, only the novice will require an
explanation of the varied productions possible by means of the
processes already given. As actual examples, reference may be had to
the illustrations in this work. Figures 1, 2, and 3 are specimens of
line work, zinc etchings made from pen and ink drawings. The figures in
the following chapter were made in the same way.
[Illustration: Fig. 13.]
Figures 4, 5, 6, and 7, as well as some others, are zinc etchings
reproduced from Mr. Mörch’s work. With them more effort has been made
to secure half-tone by a variety and quantity, or filling, in of lines.
The example below was made by using the objects (ferns) themselves as
the negative, without any interposition from photography, and shows one
of the possible applications of zinc etching. It is delicate work and
is very beautiful when carefully done. An example of true half-tone,
obtained in the manner described in Part II., is the one which follows.
It was made by Mr. F. E. Ives, the earliest inventor of a half-tone
process, several years ago. The larger examples of half-tone work which
appear in this book are made after the most modern fashion and formulæ,
as described in Part II., and will serve well to show what the worker
in this fascinating process may expect to reach after patient and
persistent experiment. When we look upon Fig. 1 and see the very best
that zinc |118| etching could do a few years ago, and compare it with
the Mosstype and other half-tone pictures now possible, we may well
wonder at the growth of the art.
[Illustration: Fig. 14.]
It has been attained by the careful and persistent plodding of a few.
Many a method has been discarded for a newcomer, and there is no
telling what may come next. Photography has about revolutionized the
illustration of books and magazines, and has made the newspaper far
more attractive than it was a few years ago. It has made the faces of
almost every renowned individual familiar in every land and in every
household, and the attractions of every known country have been so
pictured by it that every intelligent child is familiar with them. It
has been said that process-engraving has supplanted wood-engraving.
This is not so. How many newspapers were illustrated before
process-engraving was made available? How many works of the old masters
and gems of the old museums abroad were made familiar to the lovers
of pictures everywhere, by wood-engraving? Instead of coming into the
arts to take the place of another, photo-engraving has made a place for
itself and a market for itself. Moreover, it is refining and educating
the masses by creating a love for art, where before its advent, there
was very little feeling for the beautiful. Its accomplishments have
been marvellous, and yet they have hardly begun. The good photography
has done in bringing the wood-engraver up to his duty in following the
artist in every line and light and shade, it will augment by teaching
him how to secure the loveliest effects of nature. It will make way for
more wood-engraving as well as for more process-pictures if you choose
to call them such.
|119|
PART III.
PHOTO-ENGRAVING ON COPPER.
CHAPTER I.
SUBJECTS IN LINE.
In printing from copper plates, the ink, instead of being spread on
the surface of the plate by means of a flexible roller as in ordinary
type printing, is smeared over the previously warmed plate and thereby
forced into the deep parts of the plate. Then, after the surface is
polished, the paper picks out the ink from these cavities and so forms
the picture. Therefore, instead of using a negative for producing the
resist, a transparency is required; and for the production of subjects
in line, the transparency must fulfil all the conditions laid down as
required in a negative for the production of prints for zinc etching
and for photo-litho. transfers, and must be from a subject in line or
in stipple.
The negative is made the exact size required, by the wet collodion
process (the lens being used without the reversing mirror). This
negative is intensified by immersion in the bichloride of mercury
solution, and after well washing is blackened by the application
of ammonia, as directed in Part I. of this book, under the head of
photographic manipulation.
The negative must be varnished, and the margin outside the actual
subject required to be shown in the copper plate, must be masked by
means of strips of tin-foil cut perfectly straight and laid in position
squarely and symmetrically. The object is to make this margin appear in
the transparency as perfectly clear glass.
The masked negative is next placed in the carrier of the dark slide,
film up; then a couple of thicknesses of blotting paper about the
eighth of an inch square are laid on the extreme corners of the
negative. Upon these pieces of blotting paper a sensitive wet collodion
plate is placed face down. The little squares of blotting paper serve
to prevent the sensitive plate from touching the negative. |120|
The camera, with the lens out of focus, should be pointed to a large
sheet of white paper; insert the dark slide, draw the shutter, uncap
the lens, and the light reflected from the white sheet through the
lens, through the negative upon the sensitive plate, will result, after
development, in a transparent positive of the negative.
The time of exposure will, of course, vary and can only be found by
experiment. The operations of development, etc., are carried on as for
a negative.
This method of making transparencies in the camera yields the best
possible results, as the rays of light are projected by the lens
perfectly parallel, and the resulting picture is far crisper than it is
possible to obtain by exposing in the ordinary manner.
If the negative to be reproduced is already made, and is larger than
required, mask the margin by means of the tin-foil, place it in the
holder of an enlarging camera, film towards the lens if the negative
was made without a mirror; but if the mirror was used and the negative
is a reversed one, the film must be placed away from the lens.
The camera is now adjusted so as to get the image the size required,
then a sensitive wet collodion plate is used to receive that image and
produce the transparency.
The transparency for printing upon a copper plate must, when laid upon
a piece of white paper, allow every detail, however minute, to be
perfectly distinct by reflected light. If this is not so it will be
impossible to get a good engraving on the copper plate.
The transparency being secured, a plate of highly polished copper
is cleaned with a little fine whiting and alcohol, then flooded
with water. Take care that all grease has been removed (which will
be detected by the water running in streaks); next wipe the plate
carefully with a clean, soft cloth, and place it in the jaws of the
whirler mentioned in the chapter on the apparatus for zinc printing. In
the dark-room coat the copper plate with prepared bitumen (see chapter
on engraving on zinc in half-tone), and set the whirler in motion. When
the film of bitumen is dry, place it in contact with the transparency
in a printing frame, and expose it to the light (sunlight, if possible).
The time of exposure will depend very greatly upon the time of year and
day, but, in direct sunlight, ten to fifteen minutes will be about the
time.
After exposure, the copper plate is removed from the frame, and placed
in a dish containing turpentine. Keep it rocking until the image is
developed by the unaltered bitumen being washed away, then remove the
plate from the dish, |121| and wash it well under the tap. When quite
dry, coat the back and edges of the copper with ordinary black varnish
laid on with a camel’s-hair brush, so as to prevent the mordant to be
used from attacking the back.
Alterations and additions may now be made by means of transfer ink
thinned with turpentine, applied by a sable brush, or by means of an
etching needle or scraper, remembering that the etching needle or
scraper will make a black line and the transfer ink will cause a white
mark, or exactly the reverse of a type block. The plate is now ready
for etching in a
Saturated solution of Perchloride of Iron 2 ounces.
Water 10 ounces.
Use a porcelain dish for the solution. Immerse the plate, and keep it
rocking for about ten or fifteen minutes, then remove it, and wash
it under the tap, rubbing it gently with cotton-wool. After drying
it, warm it slightly, then roll up with a glazed leather roller, or a
smooth India-rubber roller charged with the hard ink used during the
clearing-up of the zinc block, viz.:
Beeswax 1/2 ounce.
Resin 1 ounce.
Shoemaker’s Wax 1 ounce.
Litho-printing Ink, black 2 ounces.
Melt together. When cool, mix with turpentine to the consistency of
soft soap.
The roller is charged with this ink, and the plate warmed and rolled
up, so as to close up the high lights and half tones, leaving only the
deepest portions bare. Immerse in the etching fluid again for about
three minutes, rocking during the immersion, and finally wash the plate.
Next remove the resist of bitumen, by means of turpentine, and take
proofs in the press. If deeper etching is required, proceed as before.
The following is equally satisfactory, and a little quicker:
Fuming Muriatic Acid (sp. gr. 1.190) 10 parts.
Water 70 parts.
To this is added a boiling solution of
Chlorate of Potash 2 parts.
Water 20 parts.
This is diluted for use by adding 1 part to from 100 to 400 parts of
water.
The time of immersion in either of these mordants is ruled by the
temperature of the room and of the liquids used. One or two careful
trials will soon give the desired information.
|122|
CHAPTER II.
HALF-TONE INTAGLIOS.
We now come to quite a different class of work, namely, the production
of half-tone intaglio plates. They may be produced in many ways, each
way giving results quite unlike the others.
The first process is based on the half-tone method given for
typographic blocks, modified to suit intaglio.
In this, as in fact with ALL methods, we must first of all produce
a satisfactory transparency. That is best done by reproducing in an
enlarging camera.
Place the negative, with the subject masked with tin-foil, in the
window, then focus upon the ground-glass screen of the camera the
requisite size; then prepare a wet collodion plate, and, having fixed a
grained screen* in front of the carrier, put the plate in its place,
then expose to the light and develop as directed for wet collodion
pictures; the result, however, will be a positive and not a negative,
and instead of the grain being interspersed through the high lights,
the shadows will be grained.
* The grained screen is a copy from a proof from a fine ruled
copper plate. See Chapter on “Half-tone Blocks on Zinc.”
The transparency must be made in this manner—_i. e._, from an ordinary
negative with a screen in front of the sensitive plate, so that the
shadows and half tones are grained or broken up. This would not be
the case if the transparency was made from a negative grained for
the production of a type block, as in such a negative the blacks are
represented solid and the lights and half-tones grained should be made
on large sized plates.
The transparency made must fulfil all the conditions necessary for the
production of type blocks—_i. e._, the film must be perfectly free from
veil or fog; it may be varnished or not.
The mark put upon the negative from which the transparency is made,
will cause the edges of the transparency to be quite clear. Coat a
clean piece of polished copper with the bitumen solution, using the
whirler as before; then |123| place the transparency in the printing
frame, film up, and place the bitumen coated copper plate in position,
so that the image is quite in the centre of the plate: fasten the
printing frame and expose to the light.
The exposure will, of course, vary according to the strength of the
light, and should always, if possible, be made either in direct
sunlight or by electric arc light.
The development is effected by immersion in turpentine, and with the
washing and drying, has already been described.
The image on the copper plate being satisfactory, it may be retouched,
if necessary, then immersed in either of the etching fluids described
in the last chapter.
Rebiting, if necessary, may be done after rolling up with the resist
ink there given, but care must be taken in this rebiting to guard
against interfering with the grain of the plate.
|124|
CHAPTER III.
HALF-TONE INTAGLIOS—(_Continued_).
The next process under consideration is that in which the grain is
given to the copper plate by dusting it with fine powder of resin
(colophony) or of asphalt. To do this a dusting box is required, which
may be an ordinary aqua-tint box hung on centres for the purpose of
revolving it when desired to cover large plates with the powder. The
following figure will illustrate a box suitable for small work.
[Illustration: Fig. 15.]
The box should be eighteen inches high, twelve inches wide, and eight
inches deep; it may be made of cardboard with the inside quite smooth.
It should be closed all around except at A, where there is a small door
four inches high; the bottom of the box is either studded with small
nails or some coarse wire netting is stretched across, upon which the
copper plates can rest, as near level as possible. To use this box,
four ounces of resin or asphalt are powdered in a mortar until quite
fine. The powder is placed inside the box, and the door closed; the box
is now vigorously shaken, then placed on the table, the door opened,
and a copper plate (previously cleaned and polished) is at once placed
face up on the nails or wire netting. By the time the door is opened
and the copper plate or plates are in position, the coarser particles
of the resin will have subsided, leaving only the fine dust floating in
the interior of the box; now close the door, and leave the copper plate
within until it is judged that it is powdered sufficiently, which, of
course, will be a matter for the operator to find out by practice.
When the plate has been sufficiently powdered, it is carefully
withdrawn and placed upon a hot iron plate and allowed to remain there
until the resinous |125| powder is just sufficiently melted to adhere
to the copper plate, preserving as much as possible the separate
existence of each atom of dust. Take care to stop the action of the
heat before the resin is melted completely and made to run together and
form a smooth surface.
The heat having acted long enough, carefully withdraw the prepared
copper from the hot plate and allow it to cool. Any desired quantity of
these plates may be prepared and stored away for future use. When they
are required the grain may be selected to suit each picture, as the
operator can prepare at will (after practice) either a coarse or a fine
grained ground.
Instead of using a hot plate the resin may be melted over a gas flame,
but the hot plate will be found the best.
There is another method of laying this aquatint ground that is simple
and novel, viz., by using the air brush. Those who are in possession of
this instrument need no further instructions than to be reminded that
ordinary bitumen dissolved in benzole, or a resinous-spirit varnish,
is placed in the color reservoir, and then the brush will coat the
clean copper plate with an aquatint as fine or as coarse as required,
according to the distance between the plate and the “brush.” Another
advantage with this method of laying the ground is, the ground need not
be even, as in the dusting method, but the artist may lay the ground
coarse in some places and fine in others, _verb sap_.
The next step in this process will be to get a transparency of the
subject. This may be made by any known process (at last, some one says
we are getting away from the wet collodion) so long as it is clean,
vigorous, and free from fog.
The transparency being at hand, that portion of it required to be
transferred to the copper plate is carefully surrounded by a mask of
tinfoil, or of non-actinic paper, which will serve as a safe edge to
the carbon tissue to be used in making the negative resist, as well as
to keep the margin of the plate free from extraneous picture.
This done, a piece of sensitive carbon tissue, a little smaller than
the copper plate, which has been previously sensitized with bichromate
of potash and dried, is placed upon the masked transparency and exposed
to light until sufficiently printed; the tissue is then removed from
the printing frame and placed in a dish of clean cold water; then one
of the copper plates with aquatinted ground is also placed in the
water, and the face of the tissue and the copper plate are brought in
contact. After adjusting the tissue on the copper |126| plate, the two
are withdrawn from the water, laid upon a bench, and a squeegee passed
over the back of the tissue. Thus the driving away of the water from
between the two surfaces will cause the tissue to adhere to the copper
plate.
Now let the plate stand a few minutes, then immerse it in a dish of
warm water at about 90° F. As soon as the tissue compound is melted,
lift away the paper backing and throw it aside, then gently lave the
copper plate with the warm water until all the soluble pigmented
gelatine is dissolved; after that wash it under the tap, and place it
in a strong solution of alum for fifteen minutes, and again wash and
allow to dry.
When the gelatine image on the copper plate is quite dry, the margin
outside the picture is coated with bitumen or spirit varnish, then the
plate is placed in the etching bath of perchloride of iron (see page
121), in which it is allowed to remain until the high lights under
the thickest portions of the gelatine image just change color; then
remove it and wash it under the tap; next clean off the resist image,
and after drying and cleaning up, try a proof. If necessary, ink up as
directed in Chapter I., page 121, and rebite.
To succeed with this process it is only requisite to have a well-laid
ground, a good, vigorous transparency, and the carbon tissue in good
working order.
* * * * *
N. B.—In order not to confuse the above directions by interpolating the
working details of carbon printing, these will be given in a chapter
further on, together with formulæ for making suitable tissue.
|127|
CHAPTER IV.
HALF-TONE INTAGLIOS. ELECTROTYPING METHODS.
The preceding methods of obtaining intaglio plates have been by the
etching process. We now try another method whereby the printing plate
is obtained by depositing a film of copper upon the photograph, and
from this copper electrotype the prints are to be made.
There are many ways of proceeding to make these copper intaglios, the
grain being obtained in many ways, but the foundation is the same in
all, and consists of incorporating bichromated gelatine with grit of
such a nature as to cause the image to be rough instead of smooth, or
else the roughness is given to an ordinary or modified so-called carbon
image developed upon a silvered copper plate.
The silvered copper plates upon which the gelatine images are to be
developed are prepared by dipping clean polished plates in a solution
of cyanide of silver, made by adding cyanide of potassium solution
to a solution of nitrate of silver until there is a slight permanent
precipitate. The copper plate remains in this for three or four
minutes; it is then removed, washed under the tap, and dried.
The gelatine tissue compound is had by first of all making a jelly of
Gelatine (soft) 8 ounces.
Sugar 5 ounces.
Water 25 ounces.
Soak the gelatine until soft, then melt it at as low a temperature as
possible, add the sugar and churn all for fifteen minutes; then add to
one-half of the jelly one ounce of finely powdered graphite, and to the
other half one ounce of a coarser powdered graphite. Churn these well
together.
Paper is coated with the above mixtures, floating it first upon that
containing the coarser graphite, then after drying, coat again by
floating the paper upon the gelatine containing the fine graphite, and
again drying.
The paper is then sensitized by being immersed in a three per cent.
solution of bichromate of potash. Dry it in the dark. After exposure
to light under |128| a _negative_, it is developed upon the silvered
copper plate, after which the electro is made.
Another plan is to expose a piece of ordinary carbon tissue under a
negative in the usual manner, then develop it upon the silvered copper
plate, and sift over the wet gelatine image some finely powdered glass,
sand, or emery which has been previously soaked in paraffine. The
gelatine is then allowed to dry, when the grit is brushed away, leaving
the gelatine image all marked and pitted. This pitted image is then
black-leaded, and the electrotype is taken from it.
Another method is to place the newly developed carbon print on the
copper plate, inside the aqua-tint box, Chapter III. (having previously
shaken up the powder); when it is well dusted over, allow it to dry,
and then remove the powder by dissolving it out with either alcohol,
turpentine, or benzole, after which the electrotype is made.
|129|
PART IV.
PHOTO-LITHOGRAPHY IN LINE.
CHAPTER I.
This process is for making photographic reproductions of a subject in
black lines on a white ground, half-tones and shadings being indicated
by hatching, or stipple, but no washes of color are permissible. The
object sought for from such a subject is to produce a transfer which
can be laid down upon stone or zinc, and proofs printed therefrom in
the ordinary lithographic press or machine.
To gain this end there are three methods: the first, by printing upon
paper prepared with bichromated gelatine, the lines of which, after
exposure to light under a direct negative (_i.e._, a negative taken
without a mirror behind the lens), will retain ink, whilst the gelatine
protected from light absorbs water, and rejects the ink. The result is
a replica of the original in fatty ink, and may be transferred to stone
or zinc, and printed from by the usual lithographic method.
In the second method, a print is made upon zinc from a reversed
negative (in the same manner as directed in Chapter V., Part I.) in
bichromated albumen, which is rolled up in transfer ink, and from
that a transfer is pulled on Scotch transfer paper, which may then be
transferred to stone or zinc, and printed from at a litho. press or
machine.
In the third, and by far the best method, the print is made from a
reversed negative on zinc, in bitumen, as directed in Chapter V., Part
I., then rolled up in transfer ink, the transfer pulled on Scotch
transfer paper, then transferred to stone or zinc, and printed from at
a litho. press or machine.
The defects inherent to the first method are, first of all, in the
preparation of the gelatine paper; this is tedious and messy. Then
there is always danger of breaking the lines in transferring, and also
the difficulty of working exactly to scale. |130|
The second method is quick, easy, and simple, the only drawback being a
tendency of the lines to thicken. With this and the third method there
is no difficulty in getting absolute scale.
The third method is perfect, and presents no drawbacks.
The two latter methods having been amply explained in Part I., it will
not be necessary to redescribe them, except to explain that when the
print is made on the zinc in albumen, it is gummed in, fanned dry, then
damped off with a wet sponge, followed by a damp cloth, rolled up with
transfer ink, and the transfer pulled upon good Scotch transfer paper.
The same remarks apply to bitumen prints.
For a transfer printed in bitumen, the image is developed in
turpentine, and when this is completed, wash the plate thoroughly under
the tap, then immerse it in the graining bath (Part I., Chapter I.,
page 24), and keep the tray rocking for a few minutes; the effect of
this will be to destroy the polished surface of the metal, substituting
a pearly matt surface, which will show up the picture properly, and
allow the operator to judge whether any of the fine details are
wanting; if there are, it will be necessary, if the details are
dissolved out, to repolish the zinc, first with pumice-stone, then with
snake-stone, then with pumice powder, finishing with fine rouge; then
coat with bitumen, whirl, and again expose to light, giving this time,
longer exposure under the negative.
But if the fine details are buried in undissolved bitumen, a further
immersion in the turpentine bath will soon clear them; then again wash
under the tap, immerse in the graining bath, again wash, then, with a
sheet of clean blotting paper, remove the surplus water, and allow the
surface to dry in a cold current; but beware of using heat, as it has a
tendency to make the bitumen image refuse ink in rolling up.
The zinc being dry, it is gummed in, fanned dry, then the gum is
washed off, and the image rolled up with a leather roller charged with
transfer ink. As soon as the bitumen has taken the transfer ink all
over, a transfer is pulled upon Scotch transfer paper, which in turn is
transferred to stone for printing from.
In rolling up these prints upon zinc, care must be taken to keep the
surface (whether the image is in albumen or bitumen) properly damp.
The preparation of paper transfers will be treated upon in the next
chapter.
The negative from which these transfers are made, must have all the
characteristics of a good negative for printing on zinc for etched
blocks, viz., the lines |131| must be represented by clear glass, and
those portions of the negative representing the whites of the original,
must be as near opaque as possible.
The subjects to which photo-lithography is applicable, are those that
are strictly in line, or stipple, or dots, or cross hatched, or chalk
drawings; in fact, any subject that may be done by lithography, or in
black and white; but no shading by color washes is permissible.
Transferring to stone or zinc is done as follows:
First of all, the transfer is trimmed to proper size; it is then placed
in a damping book, made by placing wet sheets of brown or good printing
paper alternately with dry sheets, then placing all under a weight for
a few hours, until the whole of the book is evenly damp; the trimmed
transfer is allowed to remain here until limp; it is then sponged on
the back with a very little of oxalic acid (half an ounce), water
eighty ounces; now lay the transfer carefully down on a perfectly clean
and polished stone, backing the transfer with a piece of smooth paper.
Having adjusted the pressure of the scraper on the stone, pull through
twice, then reverse the stone in the press, and pull through twice
more. Then remove the backing and lift the transfer from the stone,
when the whole of the ink should be upon the stone, leaving the paper
quite clean. Now, if the picture is quite satisfactory, wipe the stone
first with a wet sponge, then with a damp cloth, then gum in and allow
to dry, and, if possible, to stand with the gum on all night.
|132|
CHAPTER II.
PAPER TRANSFERS.
Paper for photo-lithographic transfers may be made by coating bank post
paper or a good hand-made writing paper, with
Gelatine (Nelson’s) 2 ounces.
Water 20 ounces.
Put the above into a wide-mouthed bottle or jar, and allow the
gelatine to soak until soft; then place the vessel in a large saucepan
containing cold water, and set on a fire, or over a gas-burner, and
by the time the water in the saucepan is hot the gelatine will be
dissolved. Then add slowly (stirring the gelatine with a glass rod) one
drachm of a ten-grain solution of chrome alum. Now strain the gelatine
solution through fine muslin into a clean dish, standing it in a larger
dish containing hot water; float the bank post paper upon this solution
(taking care to avoid air-bubbles) for two minutes, then lift it off
slowly and hang it up to dry, pinning it by two corners to the edge of
a shelf.
When dry, the operation is repeated, but this time the paper is hung
up to dry by the two opposite corners, so as to equalize the coat of
gelatine.
When dry a second time, it must be floated for two minutes upon
White of 5 eggs.
Water 13 ounces.
(Shake up well, and filter into a cold dish.)
Paper prepared as above will keep for any reasonable length of time.
For use, it is drawn slowly through a solution composed of
Bichromate of Potash 1-1/2 ounces.
Water 20 ounces.
Alcohol 5 ounces.
Liquor Ammonia 10 minims.
This being done, the paper is again hung up to dry, this time in a dark
room.
When dry, the paper should be laid face down, upon a polished litho.
stone, and be pulled through the press three or four times, so as to
get the surface as smooth as possible, and insure absolute contact.
|133|
This must be done in a yellow light, or in a room lighted by gas or oil
light.
The paper is now placed in contact with the negative, in a
printing-frame, and exposed to light; the exposure for such paper
should be from five to fifteen minutes.
Note well that these paper transfers are printed from negatives taken
direct in the camera, without the intervention of the mirror, therefore
negatives suitable for printing paper transfers will not do for
printing upon zinc, or _vice versa._
The progress may be watched by undoing one side of the back of the
frame, and examining the image in the dark room; but in damp weather
this should not be done too often, as the paper may expand or contract,
and blur the image.
The exposure to light under the negative being complete, the print is
removed from the frame in the dark room, and is next coated with a thin
film of ink as follows:
A smooth litho. stone is carefully coated with a fatty ink by means of
a leather roller, extreme care being necessary to insure an even coat
of ink over the stone; this being attained, the exposed print is laid
face down (the room being lit by yellow light or gaslight) upon the
inked stone, then a piece of backing paper laid upon it, and pulled
through the press, with a good nip upon it; pull it through twice,
then reverse the stone on the press, and again pull through twice,
which will leave a fine, thin film of ink upon it. Now take the inked
print, and place it in a tray of clean, cold water, allow it to remain
therein for five minutes, then lay the print upon a piece of glass,
and rub it gently with a pad of cotton-wool—previously wetted in the
water. This will remove the ink from those portions of the paper that
were protected from the action of light by the opaque portions of the
negative, representing the whites of the original.
The application of the pad of cotton-wool is continued until the whole
of the picture is cleared from superfluous ink, and the lines composing
the image are evenly coated with ink. The ink adheres only to those
portions of the paper which the light has acted upon, through the
negative.
Now wash the transfer under the tap, then hang it up to dry. When dry
it is ready for transferring to stone or zinc.
To transfer to stone or zinc, place the transfer first of all in the
damping book, and when limp place it upon a clean, cold, polished
stone, and pull it through the press. |134|
When transferred, the image is treated in exactly the same manner as an
ordinary transfer on stone or zinc.
The enamelled double transfer paper sold for double transfer carbon
work may be used for photo-litho. transfers by floating it upon
Albumen 5 ounces.
Water 20 ounces.
Saturated Solution of Bichromate of Potash 3 ounces.
Liquor Ammonia 10 drops.
and then dried.
Paper thus prepared must be kept in a dry air-tight case, and just
before using is laid face down upon a smooth litho. stone, and pulled
through the litho. press. After this, it is placed in contact with the
negative in the printing frame, and exposed to light until the details
are visible. Although the progress of the action of light can be seen,
the frame must not be opened too often, or the paper is apt to expand
and blur the image. After exposure the print is inked up, developed,
and treated exactly as explained above.
The ink suitable for inking up the stone, previous to laying upon it
the exposed print, is composed of
Best Chalk Litho. Printing Ink 3 parts.
Mutton Fat 1 part.
Put the ink and fat into a small iron or earthenware pot, and place it
over a Bunsen burner, or a paraffine stove, or on the hot plate of a
kitchen stove (_but not over an open fire_); allow the heat to melt the
two ingredients, stir so as to incorporate them thoroughly; take great
care not to allow it to catch fire; if it does, at once extinguish the
flame, as the firing would be apt to spoil the ink. When thoroughly
melted and incorporated, pour into a tin, or pot, for use when cool;
the time occupied in making this ink will not exceed twenty minutes.
The mutton fat is obtained by dropping solid kidney suet (shredded)
into a pan of clean boiling water, then allowing to cool, when the fat
is taken off the surface of the water, freed from damp and stored for
use.
Another formula for the preparation of paper, to be inked up, after
printing in the same manner as the above transfers, is to coat paper
twice with the following preparation, drying between each coat:
arrowroot, 1 ounce; wet this thoroughly with 5 ounces of cold water,
stirring well with a spatula, adding more cold water, if necessary, to
moisten the lot; then pour over it 20 ounces of boiling water, stirring
all the time; if, when the 20 ounces are added, |135| the arrowroot
has not thickened, add more boiling water until it does do so; now add
1/2 an ounce of powdered bichromate of potash and stir until dissolved;
then strain through muslin into a warm dish and float the paper upon it
whilst hot, and dry at a temperature of 70° F.
If the bichromate of potash be omitted, the paper may be prepared
in quantity and stored away for future use, being made sensitive by
floating for five minutes upon
Bichromate of Potash 1 ounce.
Water 25 ounces.
Paper for either gelatine or arrowroot transfers, after keeping so long
after preparation as to be useless, should not be thrown away, but
should be again floated upon bichromated gelatine or arrowroot, and
after drying will give finer results than new paper.
Prof. Husnik’s photo lithographic transfer paper is obtainable in
England and in America. He recommends the following chromate bath:
Bichromate of Ammonium 1 ounce.
Water 15 ounces.
Alcohol 4 ounces.
Liquor Ammonia 1 ounce.
Keep well corked in a dark place.
|136|
CHAPTER III.
PAPER TRANSFERS—(_Continued_).
Prepare a solution of
Gelatine 5 ounces.
Sugar 1 ounce.
Water 20 ounces.
Soak the gelatine in the water (cold) until quite soft, then melt it by
the application of heat (nothing is better for this sort of work than a
_Bain Marie_, a domestic utensil with a porcelain pan enclosed in one
of tin); then add the sugar and stir well, continuing the application
of heat until a temperature of 150° F. has been reached; now strain
the gelatine through muslin, into a clean dish placed in a larger dish
containing boiling water, the heat from which will keep the solution of
gelatine in a properly liquid state during the operation of coating the
paper.
The best for these transfers is a good hand-made writing paper, or good
bank-post.
Cut the paper into suitable sizes, leaving a little extra margin at one
end, and float it upon the hot gelatine solution as above; be careful
in laying the paper upon the gelatine, that air bells are avoided; when
the sheet is laid upon the surface, raise it rapidly, and throw it at
once over a cylinder of cardboard or of wood, and at once commence
to revolve this cylinder rapidly, first in one direction, and as the
limit of the length of paper is reached, revolve it in the other,
which motion will alternately bring first one end uppermost and then
the other. By this means an even coating of gelatine upon the paper
is secured, which is not possible when the paper is hung up by clips
directly it is taken from the surface of the hot gelatine. The cylinder
is kept revolving until the gelatine has set, when it may be hung up to
dry upon clips, or laid face up, over a line upon a piece of cardboard;
during the operation of revolving the cylinder, any air bells formed in
the gelatine coating may be removed by blowing or pricking them.
This, to my mind, is a most elegant method of coating small sheets (up
to thirty inches long) with a coat of gelatine, for which I willingly
give the |137| Royal Engineers the credit, it having been demonstrated
to me by Ex-sergeant Dalton, of that corps.
Paper coated in this manner, when dry, is ready for sensitizing; but if
coated in the ordinary manner, it should, when dry, be coated a second
time and hung up to dry in the opposite way that it was the first time.
Paper coated with gelatine solution as above, may be stocked, as the
coating does not deteriorate with time; but the operator must be
careful not to allow the solution of gelatine to get below 125° during
coating, else the surface will be sticky. The temperature of the drying
room must not exceed 70°, in fact, 60° will be best.
Paper so coated is sensitized by immersion for three minutes in
Bichromate of Potash 2 ounces.
Water 50 ounces.
In hot weather this solution must be kept cool with ice.
When the time of immersion has expired the paper is removed, and laid
face down upon a sheet of glass free from scratches—which sheet of
glass has been well polished with finely powdered talc (or French
chalk)—now squeegee the back of the paper vigorously, to remove the
superfluous solution and bring the surface of the paper into absolute
contact with the glass plate. The sheet of glass is now placed in a
rack, in the dark room, until the paper is quite dry, when it may
be readily stripped off the glass, and is ready for printing the
transfer. The operation of drying should be done in a current of air
at a temperature of about 60°, and the paper must be quite dry before
attempting to strip it from the glass.
The exposure under the negative is the same as described in the
previous chapter.
When sufficiently exposed, the print is removed from the frame in the
dark room, and at once immersed in cold water, where it is allowed
to stay for five minutes, when it is withdrawn and laid upon a piece
of plate glass, or a zinc plate, the face being uppermost; then the
loose end of the paper (provision for which must be made in cutting
the paper) is tucked under the plate, so as to hold the transfer in
position in the subsequent operations.
Now take a glue roller (the same as used for inking up the albumen
image on zinc, described in Part I., Chapter IV.), and having spread
a little of the ink described in the last chapter (chalk, litho. ink,
and mutton fat) upon the slab, charge the roller carefully with a thin
coating of ink, and then, having |138| removed any moisture from the
face of the transfer with a soft sponge, apply the inked glue roller,
rolling one way only—_i.e._, from the body (presuming that the edge
of paper tucked under the slab is next the body of the operator);
continue rolling until the whole of the lines forming the picture are
coated with ink, and the whites quite clean and free from ink. If the
roller should get wet from water oozing from under the transfer, wipe
it with a damp cloth and then roll it a few times on the inking slab,
and continue rolling the transfer. Be careful that the portion of the
transfer representing the whites of the picture has absorbed its full
modicum of water before beginning to roll up, and also that there is
not too much ink upon the roller. When the transfer is successfully
inked up, it is hung up to dry, and when dry is trimmed to size, placed
in a damping book, and transferred to stone.
The exposed transfer, after wetting, and being placed upon the plate
of glass, or zinc, may be developed in another way. First remove the
superfluous water from the surface with a soft damp sponge, then rub it
gently all over with a pad of cotton-wool dipped in a thin mixture of
ink thinned with turpentine and well mixed with a palette knife (this
ink should be a little thicker than ordinary copying ink); all the
image must be covered with the ink. The turpentine is then allowed to
evaporate, when by rolling with the glue roller from the body, the ink
will clear away from the whites, leaving the lines sharp and distinct.
Do not use too much pressure, else the ink may be removed from the
lines, in which case cover the whole picture with a fresh coat of the
thin ink, and again roll off. The subsequent operations are the same as
for the other paper transfers.
The ink for this method is made by melting over a Bunsen burner, or
paraffine stove,
Chalk Printing Ink 4 ounces.
Beeswax 1/2 ounce.
Stearine 1/2 ounce.
Resin 3/4 ounce.
When these are melted and well stirred together, set the mixture on
fire and allow to burn for three minutes, then extinguish by putting
the cover on the pot or pan, then pour it into a tin. When cold it is
ready for use.
In handling the sensitized gelatine paper for transfers, every care
must be exercised to keep the paper from being exposed to the action of
light, before and after exposure in the printing frame, else there will
be great difficulty in getting clean transfers.
|139|
CHAPTER IV.
TOOVEY’S NEGATIVE TRANSFER PROCESS.
A good smooth paper is floated for five minutes upon finest picked
Gum Arabic 5 ounces.
Water 15 ounces.
Bichromate of Potash 1 ounce.
This is dried in the dark, then exposed to light in a printing frame
under a direct negative. It is then laid, face down, upon a polished
zinc or stone, if a line subject, or on a grained zinc or stone, if a
half-tone subject; upon the back of the print several sheets of damp
paper are laid, and then the whole is subjected to very heavy pressure
in a hydraulic press, so that the water in the damp paper may be forced
through the print and dissolve the gum in the unexposed parts of the
sensitive gum coating (which is still soluble). The dissolved gum
attaches itself to the stone, whilst the exposed parts being rendered
insoluble by the action of light, the damp has no effect upon it, and
the stone is protected in those parts.
When the stone has been under pressure for a sufficient length of time,
to allow the small traces of gum in the deepest shadows to attach
themselves to the stone, the pressure is removed, the stone withdrawn,
and the paper carrying the photographic print is carefully lifted up,
leaving the bare negative image on a gummed ground. The stone is well
dried, and covered all over with a greasy ink applied by a roller or
otherwise. The ink is thus brought into contact with all parts of the
stone or zinc unprotected by the gum.
The image is then washed out with turpentine, and the gum removed by a
damp sponge, after which the stone or zinc is rolled up in the ordinary
manner with a leather roller, and is printed from in the ordinary
manner.
Of course, it will not be expected that the best results are obtainable
by so simple a process. Perhaps in no other branch of work does an
outlay of thought and time “pay” so well as in the practice of these
interesting photo-printing methods.
|140|
CHAPTER V.
PHOTO-LITHO. TRANSFERS.
TO DEVELOP PHOTO-LITHO. TRANSFERS.
_To develop photo-litho. transfers on paper_ there are two methods. The
first and oldest is, after exposure, to coat a smooth litho. stone with
a thin layer of transfer ink, by means of a leather roller, then to lay
the exposed print face down upon this inked stone, and pull it through
the press. Of course, this must be done in a dark room, or by gas or
oil light, as daylight would spoil the transfer.
Now the inked and exposed transfer is placed in water at 80° F., and
allowed to remain for three or four minutes, when it is taken from the
water and placed upon a plate of glass, and the superfluous ink is
removed by means of a sponge dipped in the hot water. If the negative
has been sufficiently opaque, and the exposure right, the image will
quickly develop, the lines retaining the ink, while that upon the
whites will come away.
Hot water is used where the coating is of gelatine only; if gum arabic,
or albumen has been used, then, after inking up on the stone, the
transfer must be developed in cold water, and cotton-wool used to
remove the ink from the whites, rubbing very carefully with very little
pressure.
Paper prepared with a thick coat of gelatine may be developed in
another way; after removing it from the printing-frame, the transfer
is inked up on the stone, then placed in a dish of cold water and left
there for five or ten minutes; then removed and placed upon a thick
glass slab, the end tucked under so that when placed on the bench
the slab will press the paper and keep it in position. Now, with a
sheet of clean blotting-paper, remove the water from the transfer,
using pressure with the hands from the end tucked under the slab;
then, with a glue roller, roll from the tucked under end until the
image is developed. Instead of inking the transfer up when dry, the
transfer may be placed in the cold water directly it is taken from
the printing-frame, and allowed to remain for ten or fifteen minutes,
during which time the image will swell, by the whites absorbing water.
Now place upon the glass slab (one end being tucked under), and remove
the superfluous water first with a |141| sponge, then with a damp
cloth; now dip a sponge in transfer ink thinned to the consistency of
cream by turpentine, and dab all over the damp transfer, then allow
it to stand until the turpentine has evaporated. Next take the glue
roller and roll the transfer until the whites are clear; only roll one
way—_i.e._, from the end tucked under the slab.
The transfers being developed, they are rinsed with clean water,
and hung up to dry in a current of cool air. If dried at too high a
temperature, the transfers will be inferior, and difficult to handle.
[Illustration: Fig. 16.]
Instead of using a slab of glass, and tucking the end of the transfer
underneath, a proper developing-board may be used as follows: A is a
clamped board 18 inches by 12 inches, by 1 inch thick; B is another 4
inches by 12 inches; these are hinged together at C, the hinges being
let into the boards underneath. Now, if the transfer be laid upon the
board A, the end placed in the aperture C, then the pressure of the
roller will cause the piece B to clamp the paper quite tight.
A few little differences in manipulation are required by the various
transfer papers found on sale in the market. For this reason I add the
instructions given by Prof. Husnik for his transfer paper.
_Making the paper sensitive._—Pour the solution in a shallow glass or
porcelain dish (such as photographers use), take hold of the paper
on two opposite ends, dip one end (prepared side _upward_) in the
solution, and draw the paper through so that the whole surface is
covered evenly with the solution; drain off and hang it up for drying
in a _dark_ room. Pins may be used for this purpose. Never _reverse_
the paper in hanging it up. Wet only as much of the paper as you intend
using at every one occasion. In hot summer weather the so prepared
paper must be used within a few hours. In cold and damp weather it
keeps good for three days. After the paper has passed through the bath
the _prepared side_ of it must not be brought in contact with anything
whatever, as the least touch will create a spot in the picture. For
pouring back the solution into the bottle use a glass funnel. It is
very advisable to run the sensitive |142| paper on a polished stone or
metal plate through a lithograph press to give a smooth surface.
_The development_ of the picture can begin after the mentioned time and
is to be accomplished with a fine, solid, and very soft sponge, rubbing
in circle-form with it over all parts of the picture until all the ink
is washed out of the lights, the lines becoming clear and distinct
and the shade properly open. The water must be changed several times,
passing always with the sponge delicately over all parts of the picture
to remove all uncleanliness from it. But never go over the picture
with a dry sponge. After washing the picture clean it is laid between
damp printing paper and slightly pressed with the hands to remove
the superfluous water. Was the exposure of the picture too _long_ it
will be very difficult, yea, impossible to develop it. Too _short_ an
exposure will lose the fine lines. The proper time of exposure will
easily be learned.
_For very fine reproductions_ the paper should be dried and inked in
the following manner:
Take a pane of glass, coat it with a fatty substance, as tallow or wax
dissolved in benzine; wipe the glass clean, so as to leave only a trace
of fat on; lay the paper in the solution about one minute, drain off
and then lay the paper face down on the glass, removing all air bubbles
by rubbing over the back with a rubber straight edge, or better, a
squeegee. When dry, the paper will leave the glass easily and will have
a glass-like surface.
_The inking._—Take common lithographic transfer ink, mix with it
one-fourth part of the photo-lithographic ink and coat a smooth stone
with an even tint, taking care not to make it too thick (a smooth
lithograph or composition roller will answer). Lay the printed picture
face down and run it through the press with a good pressure; the
picture will be covered with an even tint, showing the picture through
it.
The development is the same as above described. This later method gives
excellent results.
_Transferring._—When all the water is removed from the picture, and
while damp, lay it on the stone and make the transfer with the same
care as other transfers are made, starting with a very light pressure;
and if the paper sticks to the stone, increase the pressure. It is
advisable to wash the stone with pure turpentine, and dry it before
transferring.
|143|
PART V.
PHOTO-LITHOGRAPHY IN HALF-TONE.
CHAPTER I.
This process, like photo-engraving, has been the subject of many
applications to the Patent Office, but the first notable progress was
made by Messrs. Bullock, in 1865. They seem to have gone into the
subject thoroughly, as the elaborate and practical specifications
prove, but although the patentees issued some fine specimens of their
work, and advertised the sale of prepared paper, nothing came of it.
Messrs. Bullock’s method comprises the printing from grained stone
tile, or a stone upon which has been laid a transfer, from a stipple
plate, or a plate engraved in lines or dots—upon sensitive transfer
paper in stiff ink.
The sensitive paper, with such imprint upon it, is exposed to light
under a negative, the specks of ink forming a medium for breaking up
the half-tones.
Suitable grain may be obtained from machine stippled plates, as well as
from grained stone.
Half-tone photo-lithography may also be made by making, from a proof
pulled from a machine stipple, or a ruled plate, or a grained stone, a
wet, collodion negative, which, being stripped from its glass support
(by any of the means mentioned in the chapter on stripped films) is
placed between the ordinary half-tone negative and the sensitive
surface—zinc, coated with bichromated albumen, or with bitumen, or
either of the transfer papers treated of in Part IV.—the result will be
a grained transfer.
Grained zinc, coated with bichromated albumen, or with bitumen, and
exposed under a very thin half-tone negative, will also yield transfers
suitable for a good many subjects, but the most successful methods are
modifications of the collographic printing processes.
Transfers made by any of the methods mentioned in the following
chapters may be transferred to polished zinc, and then etched in
relief, as directed in Part I.
|144|
CHAPTER II.
INK PHOTOS.
The various methods named in the last chapter for breaking up and
transferring to stone the delicate half tints of a photograph from
nature, are in a great measure rather crude and do not give the fine
results yielded by the following modification of the collotype process,
nor are they so certain and simple in their working.
The production of ink photos is as follows: A plate of flat copper is
grained by means of graining sand and a piece of litho. stone, the
sand being put through a fine sieve (about 120 holes to the inch). The
copper plate being, first of all, well polished and without scratches,
is placed upon a flat board, the graining sand is then sieved over it,
and moistened, then with a light, firm motion of the wrist, the whole
of the surface is evenly ground. The operation of graining is very
difficult to describe, except to say that the stone muller is shuffled
all over the plate until the polished surface of the copper is replaced
by an even matt. Renew the sand when necessary. Do not try to get
through the operation rapidly by taking large circles, else scratches
are sure to result.
The copper plate being grained, it is well washed, back and front, so
as to free it from all grit, then coated whilst wet with
Stale Beer (not lager) 5 ounces.
Water 5 ounces.
Silicate of Soda (syrupy) 1 ounce.
Tannin 1 grain.
Shake well, then filter; coat the plate twice and stand it on a rack to
drain and dry. When dry swill the plate under the tap and again dry.
These plates may be prepared in advance, as they improve by keeping.
Now prepare the following solutions:
Best Cologne Glue 1 ounce.
Water 10 ounces.
When dissolved add
Bichromate of Potash, in powder 30 grains. |145|
Stir until dissolved, then add
Nitrate of Silver 30 grains.
Dissolved in Water 1 ounce.
Stir well, then add
Chloride of Calcium (crystals) 10 grains.
Dissolved in Water 1 ounce.
Stir up well, then add
Acetic Acid 1/2 drachm.
Again stir.
Warm the coated copper plates by letting them lie upon the slab of
the drying oven. The drying oven is described in the chapter on
collotype printing, and for this process the slab should be at about a
temperature of 150° F. Now strain the above mixture through muslin into
an invalid’s cup with a long spout, and holding the warm copper plate
horizontally on the palm of the left hand, proceed to pour over it as
much of the gelatine mixture as will well cover it. Do not have a very
thick film, else the grain will be too coarse; nor too thin, or there
will be no grain at all. Practice will soon enable the operator to
apportion the proper quantity to each plate. As a rough estimate, about
one fluidounce of the mixture for a plate 12 × 10 will be required.
The plate being coated, it is placed on the slab of the drying oven and
left there until dry. That will take from one and a half to two hours.
The exact temperature at which to dry these films cannot be arbitrarily
stated, as so much will depend upon the picture which is to be printed;
therefore, a few experiments will be necessary before settling down
to an exact form of working. A good plan that answers admirably is to
raise the water in the tank of the drying oven to boiling point before
coating the plate, then coat the plate, lay it on the slab, let the
water in the tank boil for a few minutes then turn out the gas and let
the plate dry.
The plate being dry it is exposed under a good ordinary (reversed)
negative until the whole of the details are well out. Time the exposure
by means of an actinometer.
After exposure under the negative, remove the plate from the printing
frame and in the dark room cover it with litho. transfer ink by means
of a leather roller, taking care that the whole of the surface is well
coated with the ink. Now place it in clean cold water for three or four
hours, then with a soft |146| sponge remove as much of the ink as will
come away. This operation will take time, as every care must be had not
to scratch the film.
Now rinse the plate under the tap and allow it to dry.
When dry soak it in cold water for half an hour, then place it on the
press (an ordinary letter press), and with a sponge and soft cloth
remove the superfluous water from the film; then roll up with a leather
roller charged with litho. transfer ink as thick as can be worked.
When the image is properly inked up pull a transfer upon good Scotch
transfer paper.
Perhaps the first two or three pulls will not be satisfactory;
therefore, it will be best to pull a few before using the transfer
paper, damping and wiping between each pull just in the same way that
is done in printing from a lithographic stone.
A good transfer being obtained, it should be given to a lithographer
to put it down upon a grained stone, an operation which requires great
skill and experience. The student’s interest will be best consulted by
not attempting to give a description of how to transfer to a grained
stone.
Another formula for a sensitive coating for the copper plate is
Gelatine 1 ounce.
Water 6 ounces.
Soak the gelatine till soft; then melt, and add one drachm of
bichromate of potash in powder; stir until dissolved; add twenty grains
of good fresh dextrine and let the mixture cool to about 120° F.;
then add one drachm of liquor ammonia and six ounces of alcohol. The
subsequent operation of coating, etc., is the same as above.
|147|
CHAPTER III.
HUSBAND’S PAPYROTINT PROCESS.
This is a process for the production of photo-lithography in half-tone,
direct from the negative, without the intervention of a collotype plate
from which to pull the transfer, and is a distinct step in advance.
This process has been named papyrotint, being a modification of Captain
Abney’s improved method of photo-lithography, named papyrotype. It is
specially adapted to the reproduction of subjects in half-tone, such
as architectural drawings in monochrome, or subjects from nature, and
it is inexpensive. Its advantages over other methods of half-tone
photo-lithography are, that a transfer can be taken in greasy ink, for
transfer to stone or zinc _direct_ from any negative, however large,
without the aid of a medium, the grain or reticulation being obtained
simply by a chemical change. The transfer paper being in direct contact
with the negative, the resulting prints are sharper than by those
processes where interposed media are used; whilst the same negative
will answer either for a silver print, platinotype, or a transfer
for zinc or stone. The advantage of being able to use a non-reversed
negative is very great, now that gelatine plates have so largely
superseded those made with collodion.
The method of manipulation is as follows: Any good surface paper is
floated twice on a bath composed of
Gelatine (Nelson’s Flake) 8 ounces.
Glycerine 1-1/2 ounces.
Chloride of Sodium (Common Salt) 2 ounces.
Water 50 ounces.
Great care should be taken that the solution is not overheated, and
that the paper is coated without bubbles. It is then dried in a
temperature of 60° F. The paper will take about ten hours to dry, and
in this state will keep for years. When required for use, it should be
sensitized by floating on, or immersing in, a bath of
Bichromate of Potash 1 ounce.
Chloride of Sodium 1/2 ounce.
Ferridcyanide of Potassium 100 grains.
Water 30 ounces. |148|
This need not be done in a dark-room, as the solution is not sensitive
to light.
The paper, after sensitizing, is dried in a temperature of 70°, and in
a dark room. When dry, it is exposed under any half-tone negative, in
the ordinary printing frame. It is preferable to print in sunlight,
and, for negatives of medium density, an exposure of three minutes is
required; but the exposure will vary according to the density of the
negative. The correct time of exposure can best be judged by looking at
the print in the frame. When the image appears on the transfer paper
of a dark fawn color, on a yellow ground, the transfer is sufficiently
printed. It is put into a bath of cold water for about ten minutes,
until the soluble gelatine has taken up its full quantity of water;
then taken out, placed upon a flat piece of stone, glass, or zinc
plate, and the surface dried with blotting paper.
The action of the light has been to render the parts to which it has
penetrated through the negative partly insoluble, and at the same time
granulated. A hard transfer ink is now used, composed of
White Virgin Wax 1/2 ounce.
Stearine 1/2 ounce.
Common Resin 1/2 ounce.
These are melted together in a crucible over a small gas-jet, and to
them are added four ounces of chalk printing ink, and the mixture
reduced to the consistency of cream with spirits of turpentine. A
soft sponge is saturated with this mixture and rubbed gently over
the exposed paper (in this stage the nature of the grain can be best
seen). An ordinary letter-press roller, charged with a little ink from
the inking slab, is then passed over the transfer, causing the ink to
adhere firmly to the parts affected by the light, and removing it from
the parts unacted upon. It will be found that with practice, rolling
slowly and carefully as a letter-press printer would his form, the ink
will be removed by the roller according to the action that has taken
place by light, leaving the shadows fully charged with ink, and the
high lights almost clear, the result being a grained transfer in greasy
ink. The transfer is next put into a weak bath of tannin and bichromate
of potash for a few minutes, and when taken out the surplus solution
should be carefully dried off between clean sheets of blotting paper.
The transfer is hung up to dry, and when thoroughly dry, the whole of
the still sensitive surface should be exposed to light for about two
minutes. A weak solution of oxalic acid should be used for damping the
|149| transfer (about 1 in 100), and this should be applied to the
back of the transfer with a soft sponge. After it has been damped about
four times, it should be carefully put between clean sheets of blotting
paper, and the surplus moisture removed. A cold polished stone is then
set on the press, and when everything is ready the transfer is placed
on the stone and pulled through twice. The stone or scraper is then
reversed, and the transfer is again twice pulled through. A moderate
pressure and a hard backing sheet should be used, care being taken not
to increase the pressure after the first pull through. The transfer is
taken from the stone without damping, when it will be found that the
ink has left the paper clean. Gum up the stone in the usual way, but,
if possible, let the transfer remain a few hours before rolling up. Do
not wash it out with turpentine, and use middle varnish to thin down
the ink.
It should have been mentioned that varying degrees of fineness of grain
can be given to the transfer by adding a little more ferridcyanide of
potassium in the sensitizing solution, and drying the transfer paper
at a higher temperature, or by heating the paper a little before
exposure, or by adding a little hot water to the cold water bath, after
the transfer has been fully exposed; the higher the temperature of the
water, the coarser the grain will be. The finer grain is best suited to
negatives from Nature, when a considerable amount of detail has to be
shown.
The coarse grain is best for subjects in monochrome, or large negatives
from Nature, of architecture, etc., where the detail is not so small.
Even from the finer grain, several hundred copies can be pulled, as
many as 1200 having been pulled from a single transfer. It would have
produced a great many more if required.
|151|
PART VI.
COLLOGRAPHIC PRINTING.
CHAPTER I.
HALF-TONE PHOTOGRAPHIC NEGATIVES.
In all the processes and methods treated of up to Part III., the
photographic negative has been what may properly be termed, a black
and white negative, the lines being rendered clear, and the portions
representing the whites of the original being as near black as
possible. The extremes of clearness and opacity in these negatives are
obtained by having the nitrate of silver bath kept and worked in a
very acid state; then the opacity is obtained by intensifying with a
solution of mercury followed by ammonia.
Now for the methods to be treated of in this part. An entirely
different class of negative is required in which the half-tones
are fully preserved, both in the shadows, and in the lights. These
half-tone negatives may be made either by the wet collodion process,
or upon ordinary gelatine dry plates. For producing them by the wet
collodion process, directions are given on page 11.
In the processes treated in Part II. the aim has been to get the
photographic half-tone broken up in such a manner that the picture
could be reproduced by the same means as an ordinary wood block, but
in collographic printing the half-tones are not (visibly) broken up,
the gelatine holding the ink in exact proportion to its exposure to
light, thereby giving a print with the smooth gradations of an ordinary
photograph.
The collographic methods are called “heliotype” and collotype. They
are analogous in principle, but differ in detail; the heliotype is
printed from a film of gelatine, which, after being dried upon a plate
of glass, is stripped off, exposed to light under a reversed negative,
then mounted upon a plate of pewter to support it during the operation
of printing from. The collotype printing surface is the film of
gelatine upon the glass or metal plate upon which it was dried. Note
also the different printing methods.
|152|
CHAPTER II.
THE HELIOTYPE PROCESS.
A heliotype print is made in an Albion or other type-printing press,
from a film or skin of bichromated gelatine, which, having been dried
upon a plate glass (finely ground and waxed), is stripped off, then
exposed to light in an ordinary printing-frame, under a reversed
negative, then removed from the frame, laid face down upon a piece of
black velvet, and the back of the skin exposed to light for a short
time. The skin is next mounted upon a pewter plate, coated with a thin
film of India-rubber, and placed upon the bed of the press, where the
skin is covered with water from a sponge, and is allowed to soak for
twenty or thirty minutes. It is then inked up, first with one roller,
and then with another of a slightly different composition; the margin
of the skin is then covered with a mask, with a suitable opening cut in
it, then the paper that is to receive the image is put into position
upon the mask. The picture is then printed.
The above is a rough outline of the process; now for the working
details.
First of all, it will be necessary to understand that the gelatine skin
from which the picture is printed must be of such a size as to allow a
margin outside the actual picture of at least two inches all around,
so that the rollers used in inking up will not overlap the margin, and
strip the skin away from the pewter plate upon which it is mounted.
For pictures 10 by 12, and under, a convenient size for the heliotype
skin will be 21 inches by 15 inches, so the present chapter will treat
entirely of skins 22 by 16, and the sizes of rollers, etc., given, as
well as formulas for quantities of gelatine, etc., will be those most
suitable for that size of skin; so if larger skins are adopted, the
quantities here given must be modified accordingly.
The first consideration will be the apparatus and materials necessary.
The first thing that commands attention is the press—an Albion or
other typographic hand press—(the pressure necessary to print from a
heliotype skin must be vertical, not scraping, therefore a lithographic
press will not do). The press must have the bed fitted with several
thicknesses of Kamptulican sufficient to _nearly_ bring a sheet of
thick zinc type high—“nearly” is said, because |153| due allowance
must be made for the pewter plate (one-eighth of an inch in thickness)
upon which the heliotype skin is mounted. Inside the tympan place a
piece of good blanket, and also provide a loose blanket to lay over the
paper when placed in position for receiving the impression.
The press must be fastened down to the floor, as plenty of pressure
will be required in printing; a bench will be required close to the
press, upon which either one large inking slab or two small ones can be
placed, as well as the stock of printing papers, and a dish of water. A
couple of good sponges are also required, as well as a supply of thick
plate paper, to blot off the superfluous water.
THE ROLLERS.
The quality of the print from a heliotype skin depends greatly upon
having good rollers at hand for inking the image; therefore, the
preparation of the rollers (two) must be made with every care. Get the
usual printing office pattern, with handles in the centre. The stocks
of these rollers are to be coated with India-rubber sponge, upon which
is cast a mixture of gelatine, etc.
First of all, procure two 12-inch rollers with handles complete, and
get the stocks coated with India-rubber sponge a quarter of an inch
thick; then, with strong twine tie down about a quarter of an inch from
each end, trimming off the edges outside the string, so as to make them
nice and round; now place one of the stocks in position upon the base
socket of a 15-inch seamless roller mould, then carefully smear the
inside of the mould with a rag saturated with whale oil (taking care
that the whole of the surface of the mould is smeared with the oil);
now place the mould in position over the stock, put the loose socket in
position at the top, when it is ready for receiving the composition for
the inking roller, made as follows—
Scotch Glue 1 pound.
Gelatine 1 pound.
Soak all night in sufficient cold water to cover it. In the morning
squeeze out the superfluous water, and in a suitable size glue kettle,
“Baine Marie,” or a jar placed in a pan of water, melt over a fire or
Bunsen burner, then add 1 pound of green treacle, mix, and add 2 ounces
of castor oil, 1 ounce of glycerine; stir well until all are thoroughly
mixed, then pour into a warm jug, and from the jug pour into the mould
as gently as possible; when the mould is full, take a piece of wood,
and tap the outside of the mould all round, from bottom to top. That
will cause any air bubbles that may be imprisoned in the mixture to
rise |154| to the surface; then, if the mixture in setting should
shrink, pour in more until the mould is quite full.
Now allow to stand for 12 or 18 hours, then remove the mould from the
block, the socket from the top of the mould, then gently push the
roller out. If due precautions have been taken, it ought to come out
quite smooth. If it does not, the composition must be melted off in hot
water, and the roller recast.
Composition for the clearing roller—Scotch glue, 1 pound; gelatine, 2
pounds; green treacle, 1/2 pound; castor oil, 2 ounces; glycerine, 1
ounce.
The glue and gelatine are soaked as before, then melted and mixed with
the other ingredients. The stock (covered with India-rubber sponge) is
placed inside the greased mould, and the roller cast exactly as before.
The rollers being pushed out of the mould, trim the ends square with
the ends of the stock, then dip the ends of each roller in hot water
placed in a saucer to a depth of half an inch, until the composition is
slightly softened. In this condition the sharp edges are rounded off
with a damp cloth wound round the fingers.
The object of thus rounding the edges is to prevent the roller marking
the picture when rolling up the image.
These rollers are not fit for use directly after casting, but should
be placed on the handles, and washed with turpentine on a slab, then
allowed to hang for two or three days, and occasionally washed over
with a rag dipped in alcohol.
When in use the inking roller should never be washed, but if the ink
upon it requires cleaning off, it should be done by rolling it upon a
clean piece of hard paper. When put away after a job, the roller should
be coated with fatty ink. Clear it for work next time by rolling it on
the paper.
The clearing roller will require keeping free from a superfluity of ink
by washing.
Instead of making the roller composition, and casting rollers, some of
the high class composition sold for type printing may be used, or the
rollers may be obtained ready cast, which will, perhaps, be found far
more economical in the long run.
PREPARATION AND CARE OF THE ROLLERS.
Leather rollers when new should first of all be warmed in front of a
brisk fire, and when warm rubbed with a piece of Russian tallow until
the leather will not absorb any more. Then allow the roller to stand
twelve hours |155| and repeat the operation; then take some middle
varnish, smear some of it along the roller, and on a clean slab roll
vigorously, and repeat the operation two or three times, scrape the
roller with the grain, then roll up in varnish, allow to stand all
night, scrape again, roll up again next day, scrape, then roll up with
collotype ink, scrape and roll up, repeating this until the roller
takes the ink evenly. After each time of using, scrape the roller
before putting away, and if, after using, the roller is likely to be
some time before being wanted again, after scraping smear it with
Russian tallow, and wrap it up in paper, scraping it before rolling it
up in the ink again.