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.

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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.

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