Georg Fritz

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.

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.

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.

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:—

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:—

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

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.

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.

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.

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.

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.