(b and c) Copies of lithographs, type, plates for printing of any kind, plates for deep printing, I make on well satinized copying paper*; in making the prints, I employ a copying ink as thick as possible, with the addition of a few drops of a thick solution of asphaltum in lavender oil, rolling a long time with but little color, so as to get a sharp rather than a heavy print.
* Instead of the paste-gelatine-chalk, I prefer to prepare the surface with a decoction of semina psyllii.
Plates for deep printing, I heat equally throughout before applying the color. Instead of color, I rub them with chemical Indian ink, wipe the surface carefully, even polish it finally with a ball and some Frankfort black. I then draw it through and again heat it uniformly, so that the copy comes off of itself. Fine, sharp transfers, with perfect relief, are thus obtained.
(d) Anastatic copies are no longer of great value, since they always turn out roughly and cannot compare with photographic copies. Although I possess a safe method, I believe that I will have to omit it on account of the limited space of my work and the minute importance of the results.
(e) Photographic fat or resin prints should be treated like ordinary prints. Moisten them on the back with water—which is preferable to placing them between moistened blotting-paper, since the drawing does not grow too wet—and wait till they are easily flexible. Drops of water on the film can and often do destroy the proof. Draw the plate through with increasing pressure and one intermediate moistening. Prints in fatty inks necessitate a temperature of plate of 35° C. Prints with dissolved etching varnish (resin) as a printing film should have from 50°–60° C. When loosening the paper avoid warming, but moisten well. Sticking of the gelatine film happens, especially with Husnik’s paper; a safe remedy is to dry the copy in strong light, after developing. Old sensitized paper, on the contrary, seldom sticks at all, and fresh paper should always be sought.
In printing with the rolling press, I observe that the rollers of the press need only once to be regulated, and that greater or less pressure can be attained by thicker or thinner covering of the print with sheets of paper. This gives much greater security than can be had when constantly readjusting the rollers. {76}
THE FURTHER TREATMENT OF THE TRANSFER.
Should we now proceed directly to etch the copy, the acid would act through the drawing, which is as yet but loosely attached to the zinc, and would at last cause the lines to appear broken, if not destroy them.
It is, therefore, necessary to replace the loose copy by a possibly dense etching varnish, attached fast to the zinc, and to produce an intimate connection between the latter and the etching varnish. Here we meet a difference between the French and Austrian methods. The former, totally based on the lithographic process, favors the use of a resinous dense color as a strengthening material, whereas the Austrian method employs an ordinary copying color and endeavors to form an etching varnish by sprinkling and melting in a quantity of finely pulverized resin. In the method of etching with copper sulphate, it was attempted to restrict the corroding action of the sulphuric acid by the following method: The drawing, rubbed with color and thinly besprinkled with resin, was slightly melted in, then sprinkled and rubbed with the finest silver graphite or real water-gold. It was thus made an electric conductor. A thin coating of copper was then deposited on the drawing, which, in point of fact, hindered the destruction of the film. At the same time, however, the process became uncontrollable, since often a deposit of amorphous copper became tightly fastened to the metallic surface. The lateral action could not well be ascertained, since the narrowest parts were often clogged with metal, without preventing corrosion from below.
The French method of etching is this: A thick solution of gum-arabic is mixed with extract of nutgalls; this is carefully spread over the surface of the plate by means of a fine sponge, and dried by a fan. Then a knife’s point full of etching color (composed of 500 grammes chalk color, 40 grammes coagulated mutton suet, 40 grammes soap, 125 grammes yellow wax, 40 grammes margarin, and 40 grammes oleine, melted in the warm bath and passed through the color mill) is dissolved in oil of turpentine, and a portion of this solution is spread uniformly on the grinding stone by means of a fine sponge, so that the latter contains a similar layer of color throughout. The fatty gum film is then washed, with a wet sponge, free from fat and acid; a fresh quantity of the gum and nutgall solution is poured out, and the copy is by degrees strengthened by rubbing on the etching color with a sponge. This is repeated until the drawing has attained the proper strength throughout. The superposed layer of gum is then washed off, the superfluous water is removed with a sponge, a wet cloth, and blotting-paper, dried with a fan, then gently warmed. {77}