PHOTO-LITHOGRAPHY
[Illustration]
BY
GEORG FRITZ
_Vice-director of the Court and Imperial State Printing Works at Vienna_
TRANSLATED BY
E. J. WALL
(_Fellow of the Royal Photographic Society_)
_Author of “The Dictionary of Photography,” “Carbon Printing,” etc._
[Illustration]
1895
LONDON
DAWBARN AND WARD, LIMITED
6, FARRINGDON AVENUE, E.C.
THE AUTHOR’S PREFACE.
Photo-lithography, with its many branches and its extended application,
when used direct and also as handmaid for the lithographer and printer
from stone, is, with the exception of phototypy and autotypy, indeed
that process for the preparation of letterpress plates which has done
the most towards making photography useful for the graphic arts, in the
artistic sense as well as from the practical point of view. And in the
near future it will be a great acquisition when it is once generally
recognized that colour plates can be prepared by photographic means
without any considerable amount of manual or artistic help. It is the
more to be wondered at that photo-lithography has not yet found that
extension and general use which it in so high a degree deserves.
I have written this book, impressed with the urgency of stimulating
the propagation of this useful process. In writing I have been careful
to avoid all those details which are for the practical worker of
minor interest—the description of the historical evolution, etc., so
instructive as these must certainly be—so that I have abstained from
many complicated and unintelligible formulæ. I leave this willingly to
a more ready writer. Starting rather from the standpoint of speaking as
a practical worker to practical men, I have recorded all the experience
which I have gained in the course of many years.
Should it occur to me in the future that it was my task to have treated
all photo-lithographic processes, with all their ramifications, in
the most complete manner, I have still the consciousness of having
described as completely as possible the practical processes, and think
that I have thus been useful to many workers, {2} and I dare say with
absolute certainty that only tested and tried formulæ have been noticed
in this book.
With the earnest wish that this book may be received with a fraction
of the goodwill with which I have worked at the writing of the same, I
present it to the technical world.
GEORG FRITZ.
Vienna.
* * * * *
On receiving this work for review I was greatly struck with the
thoroughly practical manner in which it was written, and thought that
an English translation might be acceptable to the large and ever
increasing class of photo-mechanical workers who might not otherwise
have the opportunity of reading it in the original. I have kept to the
author’s text as close as is consistent with the idiomatic construction
of German.
I am indebted to Messrs. Hazell, Watson and Viney for permission
to undertake the task of translating the work for another firm of
publishers, and I hope the translation may prove as acceptable and
useful to the readers as it has been pleasurable to me to do it.
E. J. WALL.
1, Creed Lane,
London, E.C.
{3}
INTRODUCTION.
1.—_The theory of printing from stone._ He who would study or practise
photo-lithography must first become acquainted with the fundamental
principles on which lithography rests. I find it therefore necessary
to first give in concise form a small treatise on the theory of this
process as well as on the most important materials which are necessary
in the practice of the same.
The theoretical principle of lithography is purely chemical, and is
based principally on the repulsion of water and other substances by
fatty bodies, and the alteration of these greasy bodies by acids. As
the support for this chemical opposition a stone or zinc plate is used,
which are sufficiently porous to allow grease, water, acid, and certain
resinous solutions to penetrate to a certain degree.
The fatty substances which are transferred to the stone by writing,
drawing, or transfer, are autographic ink, lithographic ink, and chalk,
the so-called transfer and photo-lithographic colours. There are also
other substances, which are used especially in photo-lithography, which
do not evidently penetrate the stone and which cannot be considered as
greasy substances, but which, as we shall see later on, have exactly
the same action.
The above-mentioned fatty substances actually penetrate the porous
stone and make it in places suitable to take more printing ink. By
the so-called etching—dilute nitric acid mixed with gum water—two
effects are produced. On the one hand the fatty bodies are altered
in chemical composition, being decomposed into the fatty acids which
combine intimately with the material of the stone—calcium carbonate.
On the other hand, the surface of the stone not covered with the
fatty substances is chemically changed, since the carbonate of lime
is converted into nitrate, which has now the property of keeping
moderately damp when moistened with water, and thus repelling grease.
If such a transfer of greasy bodies on to the stone is allowed to act
for some hours, and the fatty substances are removed with turpentine,
it will be seen that these places have a lighter colour than the other
parts of the surface of the stone, and if the stone be rolled up with
a leather roller, charged with a greasy ink, after the stone {4} has
been damped, only these places will take the greasy ink. By means of a
litho steam or hand press prints can then be prepared from this.
It is frequently necessary to make corrections or additions to the
drawing on the stone; if the stone has been already etched some means
must be used _which will remove the action of the etching_, or else the
stone will not take the greasy matter, or at least not so readily as is
desirable. Very weak acetic acid, about 1–2 per cent., will do this. If
the stone is flowed over with this dilute acetic acid or dilute table
vinegar, the action of the stronger nitric acid and the gum is stopped,
and the surface of the stone will again take fatty matter.
Before the penetration of the grease the stone is prepared by polishing
with a concentrated solution of oxalic acid. Oxalic acid poured on
to the stone would exert an etching action, but make the stone to a
certain degree capable of taking the ink. If this liquid is rubbed on
the stone with a cloth or linen pad with moderate pressure, the stone
receives a high polish—especially the hard kinds—and in this condition
the stone takes the ink well, like any flat object, but will not retain
it. If a transfer is made on to such a stone, and the same etched, the
image will completely disappear the first time the roller passes over
it. This polish can be removed with 1 or 2 per cent. acetic acid, and
the stone then has its primitive qualities. This method is used to
reverse the image, which will be described later on.
2.—_Litho stone_ is dense limestone of the mountain limestone group,
and is found in the Tertiary deposits at a depth of two to three
metres. Its constituents are lime, clay, and silicious earths, combined
with carbonic acid, but lime is in the preponderance; it only contains
a very small proportion of silica. In the stronger acids litho stone
dissolves completely. The varieties of very fine stalactitic chalk
of tolerable hardness, with flat shell-like fracture, without rust
spots, glassy crystals or impurities, and those with very even grain,
are the most useful for photo-lithography. Marble, which consists of
pure chalk, cannot be used for lithography because, on account of its
greater density, the greasy matter cannot penetrate so deeply, and
therefore such stones would give only a few pulls.
The commercial litho stones are of different colours, from whitish
yellow to greenish shining grey. The latter has a finer and more even
grain, and is considerably harder than the other kind. These two kinds
are briefly designated in the trade as “yellow” and “blue,” and the
brighter kinds are, as a rule, softer and cheaper than the darker.
The faults which the stones sometimes show differ considerably,
and these produce certain inconveniences in continuous work. Many
stones have dark and light spots, and as these spots have, as a rule,
different densities, the etching solution cannot exert the {5} same
action over the whole of the stone, and consequently in fine drawings,
autotypes, etc., there are formed bright and dark spots. This also
occurs with calcareous, speckled, and marbly stones. The very bright
stones have less density, and therefore suck up the damping solution
very quickly, and begin with repeated printing to become tinted. Stones
with calcareous, rusty or other veins split easily, especially in the
large sizes. Lime spots or lime veins, which are easily recognized
by their brighter colour, take in graining a very unequal grain. The
drawing is darker on these places, since the grain is greater according
to the softness of the stone. Such stones are unsuitable for those
photo-lithographic processes in which graining is used, such as the
processes of Orell and Füssli and Bartös. The so-called glass veins and
glass spots are crystallizations consisting of silicon, and are harder
than the other parts of the stone. On these places the fatty inks do
not penetrate deep enough, and the drawing does not adhere well, and
can be easily removed by the rollers.
The hard stones receive a much finer surface than the soft when
polished with pumice stone; they also reproduce every point, line, and
detail of the drawing much more delicately, finer, and sharper; and,
lastly, they have the advantage that they etch much more evenly, and
re-etching is easy if moderate care be taken.
For the finer photo-lithographic work, if quality and continuous
working is desired, only the good “blue” stones should be used; for
cheaper line drawings “yellow” stones free from faults may be used.
3.—_The zinc plates_ are now coming into pretty general use instead of
stones, especially in large establishments. Although their treatment
before and during printing is essentially different to that of the
stones, yet so far as regards this method of printing they come very
nearly equal to stones. At first smooth polished zinc plates were used,
but in consequence of some difficulty in using them, and the great
care necessary in choosing them, they have been almost replaced by the
prepared or oxidized plates.
Zincographic processes differ essentially in the preparation of the
plates. In the one, the plate is given a coating which has a similar
composition to a litho stone; in the other, the plate is roughened and
given a fine grain by a mechanical method, such as the sandblast, in
order that it may be then oxidized by a chemical process, with acids
or alkalies. All these processes are more or less advantageous. The
zinc plates cost about one-tenth to one-twentieth of the cost of the
stones, and this may well be sufficient grounds for the proprietors of
large establishments being interested in zinc plates, as the stones are
rather costly.
Excellent zinc plates, coated with a film or merely oxidized, can be
procured commercially in Germany and Austria. For those {6} who wish
to prepare their own plates the following tested formulæ are given:—
A zinc plate from 1 to 1·5 mm. thick is roughened by means of the
sandblast till it has a fine, even grain and appears smooth, but clean.
The following solution is prepared:—
Concentrated solution of alum 20 parts
Phosphoric acid 2 parts
Water 20 parts
or
Alum solution 10 parts
Gallic acid 15 parts
Nitric acid 2 parts
Water 30 parts
The roughened plate is first flowed over with water, and immediately
afterwards, with one of the above solutions, in the same way as a
plate, is covered with a developer. The plate is oxidized by this, and
there is formed on the surface a white precipitate. It is then washed
thoroughly under a rose tap and dried, and the plate may be either
coated with a light sensitive substance for printing or a transfer be
made on to it.
After the development or the transfer, the plate is gummed and then
etched with an etching solution consisting of—
Gallic acid 10 parts
Phosphoric acid 2 parts
Gum solution 10 parts
Water 30 parts
this being allowed to act for 30 or 40 seconds.
For repeated printing one to two per cent. of gallic acid is added to
the damping water.
If the plate has been correctly treated the print or the photo-litho
transfer will furnish thousands of good impressions, just like a stone.
Further details as to the printing on the zinc plates, or the transfer
of the chromated gelatine prints on to the same, will be found in
Chapter IV.
4.—_The greasy drawing materials_ which are necessary for lithography
are litho tusch, autographic ink, and fatty chalk.
The two first are used in the liquid state, the chalk, however, in
solid form. The ink can be obtained in a liquid form and the two
others in solid state. All three materials consist principally of
soap, tallow, wax, resin, and soot. Soap and tallow give the necessary
grease, wax and resin give hardness and consistency, and soot the
colour. The proportion of grease in the drawing materials must be
so great that even the finest lines or points of a drawing can be
well transferred to the stone, so that they may not be attacked by
the proper etching solution, and do not break away from the stone by
continuous printing. As much black as possible in the drawing materials
is pleasant for the draughtsman, but is not actually necessary for
this particular purpose. {7}
The tusch must dissolve well in distilled water and flow fine and
clean from the pen. It should be tolerably brittle, and the fractured
surfaces should be shiny. The photo-lithographer will frequently
require the lithographic tusch for additions or for corrections. The
best is the so-called Lemercier’s tusch, which is used in nearly all
works. It consists of—
Yellow wax 2 parts
Mutton tallow 2 parts
Marseilles soap 6 parts
Shellac 3 parts
Lamp black 1–2 parts
These ingredients should be melted together by boiling.
The autographic ink is, as a rule, used for drawing or writing on
paper, and the result is then transferred to the stone. Instead of
this, any litho tusch can be used, but for some work the autographic
ink is more advantageous. This ink must be thin, run easily, but not
patchily, from the pen, and must keep for a long time equal in quality
and action. It is very advantageous that specially-prepared paper is
not required, since this always makes the work more difficult; firm,
hard writing-paper is quite good enough for this work. The commercial
inks generally possess these good qualities, and if much is not
required one will hardly care to prepare it oneself. A good successful
autographic ink which draws in brown may be obtained from the following
formula:—
Marseilles soap 10 parts
Tallow 10 parts
Shellac 12 parts
Yellow wax 12 parts
Mastic 5 parts
Asphalt 4 parts
Vine soot 3 parts
Distilled water 125 parts
Originals prepared with this ink transfer as well immediately as after
several months, and ordinary well-sized writing paper can be used for
drawing or writing on.
Lithographic chalk is only prepared in the solid form for drawing on
paper direct or on stone. According to the nature of the work, it is
harder or softer, fatter or leaner. The hard kinds, which are also
usually leaner, contain more resin and less fat; the soft, on the
contrary, more grease.
Fatty chalk is composed of—
Wax 30 parts.
Marseilles soap 24 parts.
Tallow 4 parts.
Shellac 1 part.
Lampblack 6 parts.
{8}
Lean chalk is composed of—
Wax 12 parts.
Marseilles soap 8 parts.
Tallow 2 parts.
Shellac 10 parts.
Lampblack 4 parts.
For lithographic work a greasy ink is required in contradistinction to
ordinary printing ink, which consists of linseed oil and lampblack,
which would be called “lean.” For inking-up a photo-lithographic
chromated gelatine print such an ink cannot be used. In order to obtain
a good result in transferring, this ink must contain grease, soap, and
resin.
Any good transfer ink can be used for a developing ink, as this
is applied with a roller. It usually consists of equal parts of
tallow, wax, soap, some resin, and as much litho ink as all the other
ingredients put together.
That prepared by C. Kampmann, Technical Instructor in the K.K.
Lehr- und Versuchsanstalt at Vienna, contains, besides the above-named
ingredients, asphalt and gum elemi, and works well in practice.
Thin developing inks, which are distributed with a broad brush or
a pad, can be prepared by diluting good transfer ink with equal
quantities of wax, benzine, and turpentine.
A good developing ink must have the following properties: When spread
upon the print must give a clean, sharp, sufficiently dense impression,
which can be easily transferred to the plate or stone; on the other
hand, the drawing ought not to spread. The transfer should possess such
resistance that, without rolling up, it should resist a slight etching.
5.—_The behaviour of asphalt on stone or zinc._ When a stone or plate
is coated with asphalt solution and exposed under a negative, and then
washed with turpentine, the exposed parts remain insoluble, and in
this way photo-lithographs can be prepared. The asphalt here takes the
place of the fatty ink, and is, after printing, so firm and hard that
without any rolling or inking up it can be etched with a weak, gummy,
etching solution, which gives a cleaner, sharper drawing than the
other processes. The asphalt and other light sensitive resins not only
intimately combine with the stone or plate, but chemically alter the
surface of the stone, and possibly in a more advantageous way than the
greasy inks. When a properly-exposed drawing on stone is, immediately
after printing and development, treated for a long time with rectified
or Neustadt turpentine, it is completely removed from the stone, and
it will be found that the drawing appears of a somewhat lighter colour
than the rest of the surface of the stone. If this is now inked up with
a roller, these places take up the ink _without having previously come
into contact with grease_. Numerous experiments which I have made on
various lines go to show that the {9} chemical theory of lithography
has found an important enlargement with the use of asphalt.
The following are principal conclusions to be drawn from my
experiments:—
(_a._) The exposed asphalt, whether this exposure is made by printing
or whether a drawing is first made and then exposed to the light,
adheres more firmly to the stone or zinc plate than if it was not
exposed. An asphalt drawing prepared in the dark and inked up does
not adhere to the stone, and this may be explained in that the grease
cannot act through the asphalt film. Insensitive asphalt behaves in
the same way. With correct exposure under a clear negative of about 20
degrees Vogel, and subsequent development and auxiliary exposure for
about half to one hour, the drawing adheres firmly to the stone. If
the image is to be washed off, the turpentine must act for five to ten
minutes on the film, till the exposed asphalt has dissolved. If, after
washing off, it is inked up, all the places take the ink well, and
the image appears clear and plain. The image can only be destroyed by
strong acids or alkalies, which actually dissolve the stone itself.
From this it is clear that the prints neither require inking up nor
strengthening in any other way, and my experiments have proved that in
all cases the prints are, by this treatment, clogged up, and neither
gain as regards a longer run nor in withstanding etching.
(_b._) Solution of asphalt, to which oil has not been added, behaves
as described above; if, however, oil is added to it, it acts still
better as regards the keeping of the drawing, and the prints need no
subsequent exposure. Too large an addition of oil has the disadvantage
that, in developing with turpentine, the asphalt dissolves too quickly.
The images wash off and one hardly has time to examine. The exposed
asphalt, to which oil has been added, also dissolves very readily. For
the preparation of colour plates this point is of some importance.
6.—The etching and preparing solutions are those solutions which make
the stone suitable or unsuitable for taking the grease or water.
Generally these are acids and gum arabic, either used alone or together.
Of the acids the most important is _nitric acid_, the purpose of
which is to convert the surface of the stone into a nitrate, so that
the grease cannot penetrate. This acid acts even when diluted very
energetically on the stone, and produces a fine grain.
_Hydrochloric acid_ exerts a less energetic action; it leaves the stone
smoother and does not attack it so evenly as nitric acid, but has the
same result finally.
_Sulphuric acid_ ought not to be used for etching stone. It forms
calcium sulphate on the surface of the stone, and this separates from
the stone in printing and spoils the pulls. {10}
_Phosphoric acid_ may be used for etching as well as for preparing the
stone; it exerts a very faint etching action and is seldom used for
this purpose, but principally for making corrections.
_Acetic acid_ plays a very important part in lithography. It possesses
the property, even in very dilute condition, of stopping the action of
the gum and oxalic acid, and, indeed, even that of the stronger nitric,
sulphuric, and hydrochloric acids. It finds, therefore, considerable
use in negative printing, in making corrections, etc. It converts the
stone into its original condition and makes it suitable again for
taking ink.
_Citric acid_ fulfils the same purpose, but is, however, much higher in
price.
_Oxalic acid_ is not used for etching, but only for preparation of
the stone. By rubbing the stone with a solution of oxalic acid with a
pad of cloth it takes a mirror-like surface or polish, into which the
fatty ink cannot penetrate. It is used for preparing the stone for
lithogravure, negative drawing, and negative transfer, etc.
_Tincture of galls_, or instead of this, what is simpler, gallic acid,
is used in lithography. It contains plenty of tannin, and is one of the
most efficacious means of preventing the combination of the stone or
zinc plate with fatty substances.
_Gum arabic_ or some other vegetable gum is indispensable for litho
and zincography. A 10 per cent. solution of gum is generally used. It
penetrates all the pores of the stone and the plate, and gives the same
a thin but very firm film, and prevents the ink taking on these places.
If it has become slightly acid it acts as a weak etcher, and as an
addition to nitric acid it makes the same of thicker consistence and
more easily distributable. The action of gum can be removed with acetic
or citric acid; with water alone this cannot be perfectly effected.
7.—_Etching the stone._ There are two principal etchings, the _simple
ordinary or first etching_, which obviously has the purpose of giving
the drawing the necessary stability and protecting the blank places
from taking ink, and _the deep or sharp etching_ gives for combination
printing a still greater lasting power, and for large runs keeps the
drawing clean and sharp.
The ordinary etching chiefly causes the fatty substances to assume a
new chemical condition, since in combination with the stone they form
insoluble fatty salts of lime, which represent the printing surfaces.
It has, however, also the property of cleaning the blank stone surfaces
from any adherent grease, and makes the blank parts of the stone
incapable of taking ink; also it makes the drawing clearer and more
precise.
The strength of the first etching may differ, according to the
following circumstances:—
(_a._) The stone; for hard stones stand a stronger, and soft stones a
weaker etching. {11}
(_b._) The printing image; fine drawings must at first be etched with
a weaker solution; coarser drawings, on the other hand, will stand a
fairly strong etcher.
(_c._) The material with which the print or drawing has been prepared;
very fatty developing inks and asphalt stand well even with strong
etching, whereas with lean or hard inks only a weak etching should be
used.
An etching solution which is at the limit of strength, but still
suitable for a hard stone or a very coarse drawing, would irretrievably
ruin a very fine drawing on a soft stone.
Commercial acids differ considerably in strength, and it is, therefore,
better to use a hydrometer than a measure. It is also always more
satisfactory not to use the acid by itself, but in conjunction with
gum. A solution of gum of eight to ten degrees strength is diluted with
nitric acid till it measures 10 to 12 degrees on the hydrometer. This
solution may be safely used for every case, and it is only necessary
to allow it to act longer for coarser drawings; it should be evenly
distributed over the surface of the stone with a clean soft pad. In
very hot weather it acts more energetically, and then it should be
used weaker for fine work. In any case it is advisable to let the
stone or plate stand for some hours before etching, so that the ink
may thoroughly combine. The etching of zinc plates will be more fully
described later on; in other respects the treatment is the same as for
stone.
8.—_Deep-etching process._ The idea of this is chiefly to increase the
printing form and to make the stone more resistant in printing. In
working this the principal thing is to sufficiently protect the drawing
from the action of the strong acid. This is generally done by dusting
with resin, which has a low melting point.
There are two deep-etching processes which are chiefly used, one in
which the resin is melted with a spirit flame, the other in which the
same thing is done by ether vapour.
The procedure in each case is extremely simple. In the so-called
burnt-etching process, which has been perfected by Eberle, of Vienna,
the already etched stone ready for printing is rolled up with a very
stiff printing ink, not transfer ink, and then the drawing dusted
with the finest powdered resin. The stone is then gone over with a
cotton-wool pad and plenty of talc or French chalk, and then well
dusted off with a broad camel’s hair brush in order to remove all
traces of resin from the blank stone. To melt the resin a spirit lamp
with a side flame is used. The flame is passed over the drawing, and
ought only to be allowed to act sufficiently long to make the resin
combine with the ink, which can be recognized by the drawing looking
shiny. If it has been melted too long the sharpness of the drawing is
damaged. After this the etching may be at once proceeded with, and
this is effected with a solution of gum to which 8 to 10 per cent. by
measure of 44 per cent. nitric acid has been added. For fine drawings
4 to {12} 6 per cent. of acid should be used. In using this a fairly
strong effervescence takes place, which should not frighten anyone.
In the ether or cold-melting process exactly the same procedure takes
place, only that instead of melting with an open flame this is effected
by ether vapour.
For this work a wooden stick of about 2 mm. thick is laid on two edges
of the stone. On another ruler, which should be large enough to cover
the whole of the stone, and which should be covered with flannel or
stout cloth, ether is poured; this ruler is laid on the others, so that
it forms a right angle with them, and is slowly drawn over the surface
of the stone. The ether vapour falls on to the surface of the stone and
dissolves the resin which thus forms the protective film for the deep
etching, which is done precisely as described above.
Another melting process recommended by Scamoni consists in pouring
alcohol on the stone and then setting fire to it.
9.—_Differentiation of the printing processes._ Technically we
differentiate the principal printing methods into three, according to
the method of production. _The first and oldest_ is the typographic
or letterpress printing, which is founded on the principle that every
line or every point which ought to print must stand up on the plate,
and all those places which must appear white in the print must be
sunken in. The artistic effect is obtained by tones which are formed of
individual lines or points, which are closer together or further apart,
or else print finer or deeper. In printing a forme or plate, etc., it
must be “made ready,” that is to say, the pressure in printing must be
so arranged for each part of the picture that on the lighter places
or finer places less pressure must be exerted, whilst on the deeper
tones more pressure should fall, according to their gradation. This
balancing, which is technically termed “making ready,” is effected by
cutting out the delicate and building up the strong or dark parts on
the overlay. With a proper overlay the artistic effect of the picture
can be much increased; with a faulty overlay it can be quite spoilt. In
letterpress printing the artistic element lies in the making ready.
Typographic prints are distinguished by the lines, figures, etc., being
somewhat pressed into the paper, and show raised up on the back, which
is technically termed “impression.” When this “impression” is very
plain, that is to say when the printing has gone pretty deeply into the
paper, it is advisable before reproduction to remove this by strong
pressure.
The second method of printing is exactly the opposite of the first,
and is founded on the principle of printing from intaglio. The lines
and points which should print are cut mechanically (by engraving or
piercing) or chemically (by etching) into the stone. The etched or
engraved intaglio plate represents a negative, or a reversed wood-cut,
only with the difference that the lines do not {13} lay in the same
plane. In order to obtain an impression the ink is pressed into the
cut-out parts, and is wiped off from the surface of the plate. By
stronger or weaker wiping the print receives a stronger or weaker local
tone, which is of great advantage from an artistic point of view, but
which forms no small obstacle to the reproduction.
The impression is represented in relief on the paper. According to the
depth of the lines they take more or less ink, and appear therefore
raised up in the impression according to the amount of their depth in
the plate. Reproduction photography has to reckon on this disadvantage,
for with a side illumination the raised up lines cast shadows, and a
correct negative does not follow.
By the third method, lithography, of which we have already spoken,
the impression lies generally flat on the paper like a drawing, if
a very strong deep etching was not used, in which case it is also
slightly raised. In printing from the graver or from stone etching a
faint relief is generally noticeable, which is never so high as with
copperplate printing, and which is no important obstacle to making a
photographic negative.
{15}
CHAPTER I.
1. GENERAL NOTES ON PHOTO-LITHOGRAPHY.
By photo-lithography we generally understand that process by which
it is possible to prepare a printing plate or a stone by the aid of
photography from any original, whether it be a drawing, a print, or an
oil painting, either of the same size or smaller or larger than the
original, which can be reproduced in the lithographic press.
The main characteristic of this process is that either the original
from which the reproduction is to be made must be prepared in distinct
lines, strokes or points, or that any half-tone which may be present in
the photographic negative must be broken up on the stone or plate into
lines or points.
The basis for the preparation of a photo-litho is as a rule a
photographic negative on glass or gelatine, which, as the word negative
implies, when examined by transmitted light, must have all its tones
reversed, that is to say, the drawing or the lines, strokes or points
which must in the print be black, must look transparent, whilst the
other part of the negative which forms the groundwork must be covered
or opaque.
If every photo-lithographic process was to be described in detail
there would be a great many, but actually they may all be classified
according to two principal methods:—
(_a._) One, in which the stone or plate is itself coated with the light
sensitive substance and exposed under a reversed negative, so that a
reversed image is formed on the stone or plate, which in printing comes
in the right position, and
(_b._) The other, in which paper or a very thin zinc plate, provided
with a light sensitive film, is exposed under an ordinary, that is not
reversed negative, and thus is rendered capable of receiving fatty ink,
and is then transferred to the stone or plate by transfer.
Of the many processes which, though differing in detail, may, looking
to the final result, be assigned to one or other of the above-mentioned
principles, there are two which have been especially tested in
practice, namely, for _the direct transfer_, as we will call it, that
process which is based on the light sensitiveness of asphalt or of an
organic substance in combination with a {16} chromium salt; and for
_the indirect transfer_, that process which is founded on the light
sensitive chromium salt in combination with gelatine, or briefly on
the light sensitiveness of chromated gelatine. All other more or less
complicated methods have disappeared from technical practice and have
only the honour of being scientifically interesting and theoretically
correct, but for various reasons are not practically valuable.
It is indeed obvious that a discovery so important and useful to one
of the principal departments of the graphic arts as lithography is,
and which may be called even more essentially capable of variation
and multiplication, and perhaps in its way also more artistic, should
call forth an earnest movement on behalf of the technical experts,
principally with the endeavour for simpler forms and extension of its
powers of work. This, indeed, has not always been attained, and these
attempts will therefore only be taken into consideration in this book
as may appear necessary, and all others will be passed over in silence.
The methods used by some experimentalists for direct transfer, which
consist in coating the stone with a solution of gelatine, albumen,
or gum made light sensitive with a chromium salt, and after exposure
under a positive or negative, obtaining a printing plate, were in
execution complicated and troublesome, but in results fairly safe and
satisfactory, so that they are now more and more used in practice.
Iron and silver salts have been proved as not very suitable for
photo-lithography, and at the present time for direct transfer asphalt
is most generally used, and latterly also organic substances rendered
light sensitive by a chromium salt; for indirect transfer chromium
salts in combination with gelatine, or chromated gelatine.
_Asphalt_ exposed to the action of light undergoes a chemical change
which consists in its becoming less soluble in its original solvents.
This was known to Nicephore Niépce, one of the discoverers of
photography, whose endeavours to produce images by the action of light
were actually based upon this very property of asphalt. He used for
this purpose metal plates which were converted by a species of etching
into printing plates.
In the year 1852, the well-known Parisian lithographer Lemercier, in
partnership with Lerebours, obtained a patent in France for a process
by which they were in a position to obtain images on stone by the
exposure of asphalt, and thus reproduce the same by printing in the
ordinary way. They coated a lithographic stone with ethereal solution
of asphalt, exposed it under a negative and developed it with ether;
there remained behind then the parts which had been rendered insoluble
by light and formed a positive asphalt image on the stone, the outlines
of which had the property of taking up greasy ink and with suitable
preparation of giving an impression on paper. Such a stone was etched
in the ordinary way with acid and gum, and then it was possible to make
as many {17} pulls from it as was desired in litho ink. We have here a
practical photo-lithographic asphalt process, as it is at the present
time practised with various modifications, and which gave satisfactory
results.
Other resins besides asphalt may also be rendered sensitive to light,
and it is well-known that they also may be used with as good results as
asphalt for photo-lithography.
That the good qualities of asphalt were even earlier recognized is
proved by the fact that Negré, before the discovery of zinc etching,
exposed a copper-plate coated with asphalt solution under a negative,
washed out the places not affected by light, electroplated these blank
places in a gold bath, then cleaned the plate and deep etched it with
acid. He obtained in this way an intaglio printing plate similar to an
etching.
By using a positive with this process a relief or typographic plate
may be obtained, both of which processes are known as “gold etching,”
and were practised in the beginning of the ’50’s in the K. K. Hof- und
Staatsdruckerei.
The asphalt which is used for photo-lithographic purposes must possess
certain qualities, of which the most important is as high a light
sensitiveness as possible. With ordinary asphalt success will not be
attained, since it is only slightly sensitive to light; the so-called
Syrian asphalt is therefore generally used, which after having been
prepared is dissolved in chloroform and then benzole and oil of
lavender are added.
Professor Husnik prepares an asphalt from which all constituents not
sensitive to light have been extracted. Herr Valenta produces his
sulphurized asphalt. Both possess a far higher light sensitiveness
than ordinary Syrian asphalt, and are specially suitable for
photo-lithography.
The second, and considerably more extensively used method for
photo-lithography—a transfer process—is based on the light sensitive
property of the chromate salts in combination with gelatine, or
albumen, or gum.
That the bichromate salts possessed light sensitive properties, and
could be used for photo-lithography, Mungo Ponton discovered in 1839.
He printed on an ordinary paper, which had been rendered sensitive to
light in a solution of potassium bichromate, drawings and silhouettes,
and obtained after fixing, which was effected by merely washing in pure
water, brown images on a white ground.
Later Talbot found that the chromate salts in combination with
organic substances under the action of light altered the property of
the latter, and particularly that exposed chromated gelatine became
insoluble in hot water. Poitevin used this discovery for carbon or
pigment printing, and had produced in 1855 various pictures with this
process.
Poitevin discovered, further, that exposed chromated gelatine {18}
would not swell up in cold water and took up greasy ink, and therefore
after exposure under a photographic negative a picture could be
obtained exactly inversely corresponding to the tones of the negative;
and that these places affected by light could be inked-up and printed
from, or could be transferred to a zinc or stone plate, and from this
pulls could be prepared. By this discovery photo-lithography and
collotype were actually discovered.
Led on by his success, Poitevin used later, instead of gelatine,
albumen and gum arabic, and prepared with these photo-lithographic
prints, which were transferred to stone.
If a solution of gelatine is mixed with a solution of bichromate of
potash, and a sheet of paper coated with this mixture and exposed,
or if the paper is first coated with gelatine and then bathed in a
solution of bichromate of potash, various chemical changes take place
as the result of the action of light on the gelatine film, which we
will now consider.
As has already been mentioned, glue or gelatine is insoluble, and
only swells up in cold water. In warm water, however, the gelatinous
substance dissolves completely, and sets on cooling to a jelly. If a
suitable sheet of paper is coated with the warm gelatine solution,
either by floating or pouring it over it, and it be allowed to set, and
if this film is now made light sensitive in a solution of potassium
bichromate and dried in the dark, we shall have a photo-lithographic
paper which, according to the greater or less quantity of the chromium
salt used, has a more or less intense yellow colour. If the paper thus
prepared is exposed to light under a negative, or in another way if
some places before exposure are protected by black ink or strips of
paper, the places affected by light become dark coloured and brown,
and at the same time they have lost their power of swelling up in cold
water. The whole surface of the paper, that is to say the exposed and
unexposed films before being laid in water, are flat or in one plane;
if, however, the print is laid in cold water the exposed parts are not
affected by the water, that is to say they have lost the property of
swelling and remain in their original plane. The unexposed parts swell
up and appear raised up on the print, and thus make the drawing sunken
in.
The exposed places have, however, now received the property of taking
up and holding greasy ink, whilst the unexposed have taken up water and
repel greasy printing ink.
If the paper be exposed under a negative the drawing appears sunken in
after development with water; the other parts, which must in printing
appear white, are raised up; by exposure under a positive the reverse
is the case.
If these prints are in any way, either by rolling up or brushing over,
given a coating of greasy ink, the ink only adheres to the exposed
places and a print in greasy ink is obtained, which, like any other
greasy impression, can be transferred to a stone or a metal {19}
plate, which can be printed from direct, or the transfer may be
made on to a metal plate for relief etching, that is to say for the
preparation of a typographic block.
In Poitevin’s process the stone itself was coated with a light
sensitive chromated film, and exposed under a reversed negative. After
developing and careful preliminary preparation of the stone the ink
only adheres then to the places affected by light.
This is also the case if the stone is coated with light sensitive
asphalt, and the same printed on direct. After exposure the parts
not affected by light can be washed off with turpentine, benzine, or
linseed oil, so that the stone is laid bare; the places, the parts of
the drawing affected by light, however, are not dissolved. If the stone
is now prepared with the solution of gum as has already been described,
and then rolled up with an ink roller, these places will take the ink,
and by etching, etc., the stone may be so prepared that the same may be
printed from like any drawing or engraving.
By photo-lithography only line or grained drawings can be reproduced,
and half-tones, as is possible with collotype and photogravure, cannot
be obtained.
Now, with the aid of autotypic transfers and the asphalt process
on grained stones, we have a perfectly satisfactory method of
reproducing in an excellent manner half-tone drawings by the aid of
photo-lithography.
Photo-lithography in all its various branches of application is at
the present time so perfected, and rests on so comparatively a simple
principle, that a technical printer, with very little practice,
experience, and observation of the formulæ given, can attain in very
short time absolutely good results. At the same time it must be said
that frequently very great difficulties have to be contended with;
especially as regards the quality of the materials and negatives great
care must be used.
2. SUBJECTS WHICH CAN BE REPRODUCED BY PHOTO-LITHOGRAPHY.
The next question which arises is, “What can be reproduced or
multiplied by means of photo-lithography?”
The answer is, “According to the existing state of the technique of
photography and the perfection of the transfer process, everything.”
Any line or wash drawing, any oil painting or other plastic object,
any photograph of living creatures or lifeless objects—briefly, any
photograph can, under certain conditions, be transferred to stone
or a metal plate, and from this any number of impressions in greasy
ink be obtained. Before the discovery of the method of breaking up
half-tones into points or dots, only line drawings could be reproduced
by photo-lithography. Since, however, it has been possible to break up
half-tone into line or points or grain, nothing stands in the way of
reproducing by this {20} method any kind of original. This breaking up
of the half-tone into a regular or irregular grain can be effected by
means of a crossed line screen in making the negative, as in autotypic,
or half-tone, block-making, or independently of the making of the
negative, as in the asphalt process of Orell, Füssli and Co., and in
Bartös’ process and various other methods.
The undesirable half-tone must, however, always be broken up in
some way into the requisite points or lines, as it is one of the
characteristics of lithography that it is only possible to print from
distinct figures on the stone. Lithography and letterpress printing
produce impressions of sharply-defined lines or points, each of which
must form a distinct whole. Any tone which is lighter or not absolutely
black must be formed by lines or points standing in close proximity to
one another. The tonality must be formed by stronger or weaker lines
or points, by black and white spaces, or by more or less close line
and point patterns. An absolutely closed tone, as in collotype or
photogravure, is not attainable with lithography, and although numerous
experiments have not been wanting to reach this end, the same have
hitherto been without success.
The half-tones are broken up and separated into solid printable points:—
(_a._) By the autotypic transfer, which is effected by placing in front
of the sensitive plate when making the exposure the above-mentioned
crossed-line screen.
(_b._) By the so-called asphalt process, by means of preliminary
graining of the stone before coating with asphalt and printing.
(_c._) By means of the production of a grain on chromated gelatine.
(_d._) By the use of a sand blast, which is the chief point of Bartös’
process.
(_e._) By transfer of a close grating or network on to a polished
stone, which forms the basis of the litho-heliogravure process of
General-Director Chas. Eckstein, which is included in photo-lithography.
All these methods have for their purpose the breaking up of the light
tones into regular or irregular but separate points. There are other
methods besides those mentioned above which have the same purpose.
We generally distinguish two kinds of reproduction:—
(_a._) Those from line drawings, in which a negative is made without
the interposition of a cross-lined screen, and for which no other means
is used for the production of a grain, and
(_b._) Those from wash-drawings, paintings, photographs from nature,
etc., in which reproductions the half-tones are either broken up into
lines or points by the use of the screen when making the negative, or
by any of the other above-mentioned means after making the negative.
{21}
(A.) LINE DRAWINGS.
By the first method the drawing must be prepared according to certain
formula if a good negative is to be obtained which shall not require
much after work and disadvantages for photo-lithography. A poor
original may cause a partial or complete failure of the work, or
at least cause much cost and waste of time; therefore it appears
advisable to pay the necessary attention to the original which is to be
reproduced.
What a line drawing must possess which should be reproduced well by
photo-lithography in order to give a good transfer on to stone we will
now point out.
Before all things should be noted that the paper must be pure white
and smooth, yet not strongly reflective and not too weak. Smooth white
cards of medium thickness are the best to use. Since all lines of the
drawing appear in the impression of the same colour, there is not only
no purpose, but it may even be very disadvantageous to the reproduction
when the draughtsman, in order to increase the artistic effect of his
work, or to produce good perspective, etc., draws fine lines or other
points in a lighter colour. The striving of the artist for effect,
perspective, etc., so far as this is attained by lines or parts of a
lighter colour, has for this process of reproduction no advantage, but,
indeed, the disadvantage that by this the subsequent manipulations are
rendered more difficult, the whole work will turn out more costly and
finally less satisfactory.
Although from the present position of photography drawings in any
desired colour can be reproduced, yet it is most advantageous if the
originals for photo-lithographic reproduction are drawn with fine black
matt ink on smooth white papers, and the principal point to which
attention should be directed is that all lines, even the finest, should
be a good black, and should be kept of the same strength of colour as
the other parts of the drawing. The thick lines must be quite filled
up like the shadow lines of a strong letter. Shading must be obtained
by strong, fine running lines quite separate from one another. In this
the single black lines must not be too strong, and the white spaces
in between must not be too narrow, or otherwise when reduced in size
the white interstices will disappear and will finally form a solid
tone. The laying on of a tone or wash is not permissible, as even a
light tone will appear in the reproduction as a black spot. It is not
permissible also to draw on the same original with inks of different
blackness or consistency, and even if a coloured ink be used the whole
original must be prepared with one colour (red, dark blue, green, or
brown), and that as intense as possible. When we start from the only
true standpoint, that every reproduction should be a reflex of the
original as true as possible, artistic effects have from this point
of view no purpose, since the printer in printing with {22} one ink
is not in a position to give grey lines as well as black, but can
only give the appearance of everything in one colour only. He is,
however, able to give with the strongest line the finest with their
own characteristics, and can, therefore, in this direction attain the
tonality of the original.
It is obviously, therefore, the artist’s duty to draw in one colour,
and since for photographic reproduction black is the best, that is to
say Chinese ink, he will do well to completely lay on one side all
other artistic materials or effects. At the same time it should be
noted that originals drawn in any other colour can be reproduced by
photo-lithography, but if the drawing is to serve no other purpose than
for reproduction it is best to prepare it in black.
A further important requirement is that the drawing be sharply and
cleanly worked, and since the reproduction of a ragged or broken line
cannot make a full smooth beautifully running line, they will appear
in the reproduction in the same defective way, and then require at
least tedious retouching or make the printing of the subject actually
impossible. If it is necessary to cross the lines in the shadows this
must be done with great care. The points of crossing must be clean and
sharp, and the ink must not run. Too close or too frequent crossing
of the lines should be avoided, and would produce a bad and different
effect in the reproduction. Smudges or wrinkles in the original appear
in the reproduction more intense and more vigorous, and therefore it
must not be forgotten to carefully avoid these, also any tracing lines
must be erased, without, however, damaging the ink lines or rubbing up
of the paper.
Pencil and chalk drawings, assuming that they are cleanly executed,
can be well reproduced by photo-lithography, only they ought not to
be smudged or inked. Erasure marks on pencil drawings appear in the
reproduction as smudgy spots.
Drawings of architecture for illustration or other purposes, after
consideration of these remarks, can be well transferred without much
trouble by photo-lithography on to stone or zinc.
In drawings of maps, plans, etc., there are still some rules to be
observed besides the above. Boundary lines or mountain ranges with fine
hatching, waterlines for large rivers, seas or lakes, as well as the
introduction of figures, are better left out of the drawing, and can be
afterwards drawn on the stone; they will then be cleaner and sharper.
If all these details, however, must be introduced into the original
drawing, they should be executed in a pale blue colour, which will not
appear in the ordinary negative.
For plans with large letters it is better not to draw the latter, which
are frequently a lot of trouble, but to employ the simpler plan of
getting the titles, writing, legends, explanations, etc., printed by
a book printer on paper of the same colour as the original, and stick
them on the latter. The same method may be {23} adopted when preparing
railway, postal, and telegraphic charts or maps with a lot of names or
other titles, etc. The network of lines may be drawn with litho ink as
suggested above, but the names of the stations, etc., can be printed
with letterpress and stuck on in the proper places. Working in this way
not only will much labour be saved, but at the same time sharper and
more correct titles be obtained on the reproduction.
Any necessary instructions for carrying out the drawing should never be
made on the paper with red pencil, but either with pale grey or pale
blue. For this paper rubbed with indigo or graphite can be used or a
scratched gelatine proof which has been rubbed with finely powdered
milori blue.
With commercial drawings it frequently happens that ornaments are
repeated. It is not necessary for the designer to draw all the
ornamentation, which may frequently be very complicated, if it runs
over the whole of the design. It is quite sufficient, according to the
size or the number of times that the ornament occurs, for the artist to
draw it twice or three times, or sometimes ten to fifteen times; the
lithographer will duplicate it by transfer. This also applies if there
is a border, or if there are any corner or centre pieces repeatedly
used. It is quite sufficient to draw one-fourth of the frame or border,
or with very complicated designs a complete corner, and to give the
printer a rough sketch of the complete border. He will make the
necessary impression on transfer paper by photo-litho transfer on the
stone; he will also reverse the drawing from right to left, join up the
different parts, and thus construct the whole border. This applies also
to the corner and centre piece.
(B.) DRAWINGS ON BLUE PRINTS.
As a substitute for a proof cyanotype or blue prints may be used for
preparing drawings for photo-lithography and other graphic arts. When
a photo-lithograph like a pen and ink drawing is to be prepared from
a coloured picture, or from a sepia or Indian ink wash drawing of a
plastic object or a photograph from nature, or from an object not
suitable for photographic reproduction an autotypic transfer is to
be prepared, a proof of the desired object must be first prepared,
and then from this the drawing is to be made. It is obvious that the
proofs of the first-named can only be made in the original size, which
under some circumstances may not be just what is required, assuming
that the original can be used in this way. In all cases this will be
inconvenient and tedious, and possibly from the nature of the drawing
many proofs be lost. The end will be attained far more quickly and
safely if a negative is made of the original, either of the same size
or enlarged according as may be desired. The negative thus obtained is
used to make a ferro-prussiate print. {24} For this we use a good firm
drawing paper, which is sensitized in the following mixture:—
Solution A.
Potassium ferridcyanide 8 parts.
Water 150 parts.
Solution B.
Ammonio-citrate of iron 10 parts.
Water 100 parts.
When dissolved each solution is filtered and mixed in the dark room
immediately before use in equal parts. The solution thus formed is
sensitive to light and is spread on a well-sized drawing paper as
evenly as possible with a broad brush, equalized with a distributing
brush, and then dried in the dark room.
The coated side of the paper appears yellowish. It is then printed as
usual until the deepest parts look grey, as the prints look weaker
after developing. The prints are developed by floating them face
downwards on a dish of pure water not too cold, and then washed till
the drawing appears quite white on a blue ground. The washing must be
thoroughly done or else the prints turn blue afterwards when exposed to
light. These prints contain all the finest details, even in the deepest
shadows, plainly visible, and will now be the most, perfect and most
convenient proofs for the artist. The tracing or drawing is now done
with good black dull surface ink as already suggested. When the drawing
is done it is allowed to dry thoroughly, which will be in from two to
three hours. The following solution should be prepared:—
Oxalic acid 1 part
Water 10 part
which should be poured into a flat dish and the drawing allowed to lie
in it for about thirty minutes. It is then again well washed and then
immersed for fifteen minutes in a bath of
Hydrochloric acid 1 part
Water 20 part
The blue colour will now have disappeared, and the ink drawing will
appear pure black on the white paper. It should be now hung up and
dried in the ordinary way. This drawing prepared in wash or line with
ink now forms the original for a further photographic negative, which
is made in the correct size of the reproduction with or without the
intervention of the crossed screen according to the character of the
drawing. With the negative thus obtained a photo-litho on stone or
zinc, or a typographic copper or collotype plate, or a photograph on
wood for xylography may be prepared.
The use of this process appears specially important for those cases in
which an ordinary photographic negative is not sufficient, {25} for
example where a printing plate cannot be prepared from the negative.
It ought also to be useful when the light could not be controlled
in making the negative, and thus incorrect effects appear in the
reproduction, which often occurs in negatives from nature and with
polished plastic metal objects. The enlargements from the original are
then used because the details can be better seen, and the artistic
character can be more easily seen. The fineness of the drawing must
obviously be in proportion to the after reproduction, while tones may
be partly or entirely lost.
(C.) DRAWINGS ON PREPARED PAPERS.
For photo-litho transfer without the use of a screen there are some
commercial papers, toned, grain, net or pyramid grained papers which
may be used with excellent results.
On these papers, according to their preparation, various excellent
results can be obtained, which possess high claims as illustrations.
A smooth white scraper board made by Angerer and Göschl of Vienna,
which has a very even film of chalk, and which takes the lines clean
and vigorously, is especially suitable for pen and ink work. On this
paper plucky drawings like woodcuts can be executed. The perfect whites
of the paper, combined with the vigorous beautiful black, facilitate
reproduction with excellent results and without much trouble.
An ordinary writing pen and ordinary Chinese ink are used for drawing.
The ink gives sufficiently black and matt lines.
The deepest parts are covered with ink, and the desired shading or
stippling put in with the toothed scraper or engraving tool. The
shading off of the shadows may also be worked up with the toothed
scraper, and thus very delicate shading be obtained.
Two more very useful papers by the same firm are known as scraper
boards with printed lines or points, and white scraper boards with
simple or double lines stamped on to it. These papers are also coated
with a chalk film.
[Illustration: Fig. 1.]
With these papers the printed lines or dots serve as half-tones for
the artist, and by scraping with smooth or toothed scraper knives very
many effects can be obtained. Lead pencil, chalk or litho ink can be
used for drawing. For laying on, ordinary ink with a small addition of
soap may be used, and new tone effects {26} may also be produced with
a half dry Chinese ink brush, but for any drawing for line reproduction
washing with paler or darker inks is excluded. By scraping with the
smooth scraper, points are formed in place of the lines, which by
further scraping disappear entirely into white, by which means the
transit into the highest lights is effected. If a black surface is
scraped with the smooth knife a line tone is produced in the opposite
direction to the printed one. By the aid of the toothed scraper lines
in any desired direction can be obtained. When the printed tone is only
desired in parts in the picture, the other parts can be covered up
with white paper. The paper is only stuck down by the edges with mouth
glue; if it were stuck down all over with gum or starch it would be
distorted. On the white paper stuck on, drawing may be done with the
pen, and thus new effects again be obtained, as thus in a manner pen
and wash drawing are combined.
The white scraper boards without printed lines or dots are either
impressed with a single line or with lines crossed at right angles.
On this paper pen and ink drawings combined with grained tones may be
done. The outlines and everything which is to be treated like a pen
drawing may be done with a hard pen or a marten brush. Bright tones
are so worked with the brush that smooth surfaces are not formed, but
dotted darker or lighter tones. Those parts which have been laid on
quite black can be brightened up afterwards with the smooth or toothed
scraper knife or the needle, and thus many gradations obtained. Instead
of the litho writing ink pastell or very black good litho chalk may be
used for drawing. Obviously this paper also ought not to be washed or
smeared.
The pyramidal grain paper prepared by Schäuffelen of Heilbronn is also
very suitable for drawings for photo-lithographic reproduction. The
paper is coated with a chalk film of blinding whiteness, and is stamped
with a regular grain of truncated pyramids, and is produced in three
numbers. Grain No. 1 contains 2,500 regular projections per square
centimetre; grain No. 2 contains 1,500; and grain No. 3, 750 pyramids.
This paper is drawn on with litho chalk or black pastell crayons.
The deepest shadows are laid on quite black, and light effects are
introduced with the scraper or engraving needle as with the above
described papers. The same rules apply to the other parts of the
drawing.
For drawing in general or the use of effects in drawing it should
be noted that with all these papers the drawing may be somewhat
overdone, and this is necessary in order to obtain the corresponding
vigorous action in the reproduction. The printing ink is, as a rule,
never such a deep black as the drawing ink, nor is the paper which is
used for printing ever so white as the lines of the toned paper. The
contrasts would, therefore, in printing become too {27} little, and
flat unsatisfactory pictures would be obtained. With these drawings,
therefore, the two opposites, “black and white,” may be used to the
extreme, even if the drawing is not satisfactory to the artistic eye.
For making the drawing red paper ought not to be used, as when
photographed red appears dark. Then blue proof paper, or paper rubbed
with lead pencil, should be used.
A drawing for photographic reproduction ought never to be rolled, and
still less be folded; if it is to be sent away it should be packed flat.
(D.) REPRODUCTION OF PRINTS.
It is frequently required to make photo-lithographs of old prints.
As already mentioned in the introduction, we distinguish three
different methods of printing, of which the two first, typography
and lithography, are confined to the rendering of well-defined lines
or points, whilst copper-plate printing can to a certain extent
reproduce lines and tones. As regards the reproduction of the first
two, so far as their fundamental character goes, no insuperable
difficulties present themselves, when they correspond at least to
the general requirements of a drawing. Since a reproduction, with
exceptions, can never be better—obviously without very complicated
retouching—but always somewhat inferior to the original, the appearance
of the original will always be some guide as to the quality of the
reproduction that can be produced.
If, however, prints are prepared specially for this purpose, the
following points should be observed:—
1. For printing a matt surface a so-called pure white chromo paper
should be used.
2. The ink should be black and of good body, the impression clean and
sharp, every line exact and not in the least fuzzy.
The expert lithographer will easily prepare his impression. Assuming
that he has a good original stone, he will more easily make good and
correct prints from the engraving from the chalk, pen or other drawing
than the typographer. The latter has to give his impressions the
correct finish by means of overlays, without the correct making and use
of which no good picture, whether it be characters or a drawing, can
be obtained actually on a typographic press. The reader is referred
to my article in Professor Eder’s “Jahrbuch für Photographie und
Reproductionsverfahren” for 1891, where I have treated of this at
length. Prints produced by the third method, copper-plate printing,
give far greater difficulties to the photo-mechanical worker. Every
pull from the engraved plate—etching scraper drawing and photogravure
excepted—possesses a tone on its surface, which is, moreover, very
unequal, and although increasing its artistic qualities, offers,
however, considerable difficulties for reproduction. This can {28}
only be avoided by very troublesome retouching, which is frequently
prejudicial to the beauty of the picture.
If pulls are specially prepared for reproduction the copper-plate
printer must very carefully polish his plate and print without a tone,
but still this must not be done so that the plate is too strongly
polished that the depths lose their vigour; this would give an
absolutely incorrect picture as regards gradation of tone.
Etchings can, as a rule, only be reproduced with the aid of a
cross-grained screen, and the same applies to photogravures, although
the latter will seldom be required.
All tone or painted originals, such as wash or sepia drawings,
photographs from nature, collotypes, photogravures, water-colours
and oil-colours can only be reproduced by photo-lithography by the
interposition of a screen when making the negative, or by a process
in which the breaking of the tone is effected independently of the
photographic negative, and which will be described later on.
With old photographs which have faded it is as well to increase the
lights and shadows by painting.
(E.) SIZE OF THE REPRODUCTION.
A question frequently asked is, “Of what size should a drawing be made
in order to obtain a good photographic reproduction?” This question
cannot be precisely answered, for a good deal depends upon the object
itself, and on the kind of drawing.
It may be generally said, however, particularly as regards pen and ink
drawings on smooth paper, that they should never be smaller, only very
rarely of the same size; they should be drawn one-third or one-half
larger generally. The artist can execute fine details more easily and
precisely on a large drawing than on a small one.
The enlarged reproduction gives any faults or mistakes which may happen
to be in the drawing in proportionately larger size quite independent
of the fact that an enlarged reproduction is always somewhat rough and
ordinary. Reproduction in the same size reproduces the faults the same
size as they exist in the drawing; the reduction, however, also reduces
the failings of the drawing if it cannot also absolutely remedy the
same. The reduced copy has always something finer and more delicate.
The degree of reduction must be kept in mind, and the drawing be done
with this in view.
If a drawing is executed very finely and full of detail, and, besides
that, contains very small lines of drawing or titles, they do not
gain in reduction, but the opposite; they lose, as much that in the
drawing appears plain and distinguishable becomes by strong reduction
indistinct and unrecognizable, or appears to the eye as a tone. {29}
Individual cases, in which for specimen purposes or to show how far
reduction can go, many times linear, five, six, to ten times, cannot be
taken into consideration, although the effect is usually well attained.
It should also be observed that the drawing must be considered not
only as regards its size, but also the strength of the lines and
tones generally for reduction; this specially applies as regards the
tones. By reduction the tone gradations are compressed, the picture
becomes poorer in tones, and although, theoretically considered, light
and shadow, that is to say black and white, are actually distributed
in the same ratio as in the original, yet the reduced image appears
proportionately darker and loses in artistic effect.
Great reductions will, however, be useful when for some special purpose
such as the exact reproduction of geometrical figures or surface
ornaments are required, as for instance in printing designs for
cheques, bank notes, etc. In such cases the drawings should be made as
large as is necessary for the most exact and easiest carrying out of
the figures, as in this way the precision of the drawing is better kept
by reduction. In such cases, assuming that the ornaments are clear and
open without shading, the reduction may be carried beyond one-tenth
linear.
This kind of reproduction should present no difficulties either to the
reproduction or printing.
It is quite different, however, with drawings on scraper boards or
grained paper. If it is kept in mind that with too great reduction the
gradations of tone of the print will be destroyed, and that in the same
degree the difficulties of printing will be increased, care should
be taken that reduction is not carried too far. When it is further
considered that in a reproduction with 2,000 to 3,000 points to the
square centimetre the individual points disappear to the unaided eye,
and the different thick layers of points appear as closed tones, the
limit of reduction will soon be found.
If we reckon according to this view, we can assume that those kinds of
paper with coarse grain should be reduced at the most one-third, those
with a finer grain a sixth, at the most a fourth, in order to obtain
good printing plates which will give large editions. In this obviously
will a good deal depend on the character and more or less rich in
detail execution of the drawing. Still there are photo-lithographic
processes such as the asphalt process of Orell Füssli & Co., which
contains about 15,000 points, and Bartös’ process, which contains
11,000 points to the square centimetre; still for reproduction in
large quantities these processes offer many difficulties, and cannot
therefore really be taken into account when considering this.
{30}