The stone used in lithography is a limestone (carbonate of limestone) of very hard and compact texture, admitting of being ground to a fine surface. There are three qualities recognized by dealers, which are called the blue, gray, and yellow stones, of which the blue is regarded as the best, and commands the highest price. The best lithographic stones are the production of a very limited district, in the kingdom of Bavaria. Several localities are known in the United States, and some years since it was reported that a quarry had been discovered in the State of Missouri of very superior quality. The stone must have the qualities of imbibing both water and grease or oil; the crayon used in drawing upon it being composed of grease, wax, soap, shellac, and ivory-black, which is also the composition of the ink used in printing, with little variation.
The stone must be rubbed down with fine sand to a perfect level, after which it is ready to receive the drawing; a weak solution of nitric acid should be thrown over the stone. This operation will slightly corrode its surface, and dispose it to imbibe moisture, with more facility. While the stone is still wet, a cylinder of about 3 inches in diameter, covered with common printer's ink, should be rolled over the whole surface of the stone. While the wet part refuses to take the ink, the chalk, being greasy, will take a portion of it from the roller. The stone is then ready for printing.
The press consists of a box drawn by a wheel, under a wooden scraper, pressing on it with great power. After the first impression, the stone must be wetted afresh, again rolled over with the cylinder, drawn under the scraper, and so on.
The same process is employed for ink drawings, except that the solution of nitric acid must be stronger, and the printing ink stiffer.
Imitations of wood-cuts are produced by covering the stone with lithographic ink, and scraping out the intended lights. As the finer touches may be added with a hair pencil, prints far superior to wood-cuts may be obtained, but the chief advantage of wood-cuts, that of printing them at the same time with the text of the book, is lost.
Within the last 20 years the art of engraving on stone has been brought to great perfection, and at this time nearly all maps used for school atlases and by engineers, surveyors, etc., and nearly all bills of exchange, checks, drafts, and other blanks used for commercial purposes are thus engraved. The engraving is done with a pointed or sharp instrument, and is very similar to copper-plate engraving. The engraved stones are printed only when very small editions are required, transfers from these to other stones being much more easily printed.
The art of transferring and printing from transfers is now one of the most important and useful processes of lithography, and in the United States constitutes the greater part of the business of the lithographer. It is applicable to engravings on either stone or metal, and it is done from copper-plates, to a considerable extent, in maps, charts, and other engravings, which consists mainly of lines and letters, without elaborate shading. This process was invented in Europe about 30 years since. An impression is taken from the engraved plate or stone with a greasy ink, and on paper having the surface prepared with a composition which is essentially albumen. This impression is carefully applied to the surface of another stone, and on removing the paper by dampening it, and with very careful manipulation, the impression in ink remains. It is then treated with diluted acid precisely as a drawing, and becomes fixed, as it is technically called, in relief on the stone, and can be printed from with entire facility. Much care is required in this process, and the method of doing it was for some years regarded as one of the most valuable secrets of the lithographic art. Engravings of any kind can, of course, be transferred, but in finely engraved pictures, or when there is much shading, the fine lines become massed together, or blurred in transferring. In printing small maps or other suitable descriptions of engravings, printing from transfers has a great advantage over plate-printing, in the fact that several copies of the same engraving can be put upon the stone at once, and thus printed much more rapidly and economically. Maps printed from well-prepared transfers can scarcely be distinguished from those printed from copper or steel-plates.
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