Part 20 (2/2)
(8) While shading is obviated largely through enough intermixture of lampblack or other coloring substances to take away the fluidity of the printing-color, this intermixture will cause other troubles. The finer places will not take the harder color so well, whereas at other places too much will be taken. Also an impression made with much lampblack will off-set more than one made with color in which varnish predominates.
Neither will the impressions be so black. Experience teaches that a printing-color that has less lampblack will be blacker, because the sheen of the varnish will make the color strong and lacquer-like. I have tried to invent a kind of varnish that would not be so liable to shading and thus would permit a greater fluidity with safety, but lack of time has prevented me from exhausting the possibilities. I am sure, however, that it can be done, for I have found that the common linseed oil varnish can be made to lose its property of shading by admixture of fatty and resinous bodies. For instance, the addition of a slight amount of Venetian turpentine permits a greater fluidity. Very good is the following composition: Six parts linseed oil, two parts tallow, one part wax, melted together and thickened by boiling down and burning like the ordinary linseed oil varnish.
(9) The inner composition of the stone and the temperature have a considerable effect on the print and also react on the color. A stone, especially a porous one, has much less internal moisture on very warm, dry days. Then the dampening done before each impression often evaporates instantly and unequally, so that it is difficult to ink-in uniformly with a soft color or one lacking varnish, unless one wets the stone unduly, which, again, injures the impressions. In that case one must use a color that is firmer than should be used according to ordinary rule. It is also well, before printing from the stone, to lay it in clean water for a few hours, or overnight, so that it may soak in enough moisture to make it easier to dampen.
(10) If the drying of the printing-color is to be hastened, as is necessary with some work, a little finely powdered mennig may be mixed in. Finely powdered litharge of silver dries still better, but only a small amount of printing-color must be mixed with it, because it toughens within an hour. It will not keep for another day, because the mennig will dissolve after a while.
In printing from the pen design, the following must be observed:--
Even if the stone has been inked-in uniformly and well with a good color, the impression can be spoiled in various ways: if the paper has not been dampened as required by the nature of the color and the power of the press; if the pressure is not in proportion to the consistency of the color; if the sc.r.a.per is not even, and if the leather is not properly stretched.
Therefore care must be taken in printing pen designs:--
(1) The paper must not touch the inked design till the sc.r.a.per forces it down. It is not advisable to lay the paper directly on the stone. It should be in the printing-frame, which, as already described, should be so arranged that it will keep the paper at least one fourth inch away from the stone.
(2) The proper dampening of the paper is not a matter of the greatest importance in pen designs, so long as it is not too wet, in which case it causes squashed impressions, does not take color uniformly, and, if the printing-color is tough, will stick to the stone. In general, the rule holds good that the degree of dampening must be in proportion to the firmness of the varnish, and that a softer varnish permits increased dampening. Dampening is done chiefly to soften the paper, and the qualities of the paper dictate the amount necessary to a large extent.
(3) The tension of the press must be more powerful with hard printing-color and carefully graduated with soft color. Besides this, it depends--
(4) On the structure of the sc.r.a.per. If it is not absolutely uniform and well fitted to the stone, more power is needed. Thus the defect often is corrected; but this may make the color squash and spread in other spots, therefore it always is better to correct any defects in the sc.r.a.per. The sharper the sc.r.a.per is, the clearer are the impressions, because then the whole force of the pressure concentrates on the smallest area. But usually the sc.r.a.per soon becomes dull, and then the press must have more power.
(5) Insufficient tension of the leather also may produce poor impressions, especially if the color is soft and the paper very wet.
Therefore as soon as impressions appear blurred and squashed, the leather should be tautened and well lubricated with tallow.
Now we come to an important matter, namely, the correction of errors. It does not happen often that a drawing or inscription can be made entirely without error, and it would be a great imperfection in lithography if these mistakes could not be corrected at once.
Errors may be observed before etching or afterward. Different ways of making corrections are required.
It is very easy to make corrections before etching. If the error is observed as soon as it is made, while the ink still is wet, it may be corrected by merely wiping out the defect with the finger. If the ink is dry, oil of turpentine is required. In each case the ink must be well removed so that it will not resist the etching fluid later. If only tiny spots are defective they can be corrected by delicate use of a sharp eraser. Defects that need merely to be destroyed without drawing anything else in their place may be sc.r.a.ped off with a knife or with pumice stone.
After the plate is etched, errors demand treatments that differ according to whether a defect or blemish is merely to be removed, whether something else is to be drawn in place of the removed part, or if something has been forgotten and is to be added. The area of the correction also makes a difference.
If it is only a matter of removing small defects or places, delicate erasure will do. The same, or polis.h.i.+ng with pumice, is done if the area is larger. Then the corrected spots must be coated with a mixture of gum and aquafortis, using a soft brush very carefully that it may not touch any of the sound places.
If something new is to be drawn in, the process is different. Ink-in the stone very clean, and coat it with gum and water that is very thin and delicate. Let it dry. Then sc.r.a.pe the defective places away very carefully or grind them away by rubbing with pumice stone. Coat the spots cautiously with soap-water or oil of turpentine and clean off again as thoroughly as possible. (This coating is not necessary in the case of a few isolated small lines or points.) Now draw in your new design with chemical ink, and as soon as this is dry, etch the corrections carefully with a small brush and then prepare with gum.
The third case, where something has been forgotten, is treated almost the same way. If it is only a very small thing, the stone need merely be sc.r.a.ped carefully. Then the drawing may be put in, preferably with a thicker ink. If the area is large, the stone must be ground where the design is to be added, coated with soap-water or oil of turpentine, and then treated as explained before.
When the stone has been corrected and prepared for printing, it can be used at once or set aside for some length of time. In the latter case it should be inked with a firm color and coated delicately with gum solution. Then it can be held as long as desired. Coating with gum solution is advisable not merely for storing away, but for every interruption of printing that lasts more than five minutes.
If a stone has stood longer than a day without being freshly inked, it must be wiped off first of all with gum solution and oil of turpentine, that it may take the color well, so that the very first impression may be perfect. During the progress of printing, the following points are important: Uniform distribution of water, the same of printing-color, frequent inking of the inking-roller, and the very greatest speed possible.
In the main points the brush process is like that of the pen. The chief difference is that it is not possible to make the brush strokes as strong as those with the pen. Therefore, brush work does not resist etching so well and must not be treated too powerfully. Much depends on the treatment of the brush and the consistency of the ink. The brush does not permit such a flow of ink as does the pen, and generally requires one that is more fluid. A good brush ink is made as follows:--
Mix two parts of pure white wax and one part of good tallow soap into a ma.s.s not larger than a hazel nut. The ink loses its good properties quickly and should be made fresh day by day. Mix the two materials with a thick knife on a lukewarm (but positively not warm) stone, separate into small parts and moisten with rain water. As soon as the water has softened the ma.s.s a trifle, add as much lampblack as will lie on two knife points and mix the whole ma.s.s together once more till it is thoroughly mixed and quite firm. When required, a bit of this is rubbed down in a clean saucer with rain water.
As a better flow of ink is needed for brush work than for pen work, it is evident that it would not be requisite to treat the stone with soap-water and oil of turpentine, as for pen work. However, it often pays to make certain fine lines with the pen, and therefore it is better to combine both processes and prepare the stone as for pen work. It is well, however, after drying the coating, to rub it very gently with dry sand, which will not make the pen strokes flow to any extent and still will prepare the stone so that it will take the brush strokes well and not make necessary such strong etching.
If a brush design is to be etched in high relief, for ease in printing or for durability, it must be etched only to the extent absolutely required at first. Then it must be prepared with gum and inked-in with good acid-proof color. Set it aside for a while, that the color may concentrate so that it will resist the acid well, and then etch the stone to the desired degree. After etching, wash with water, coat with gum and put aside to dry. Owing to this latter procedure any fine parts that may have been unduly affected by the acid will adhere to the plate anew and it can be printed then like a pen design.
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