LITHOG'RAPHY (Gr. /am, a stone), the art of printing from stone, was invented by Aloys Senefelder, at Munich, about the end of the 18th century. It consists, first, in writing and drawing on the stone with the pen and brush, with the graver, and with the crayon or chalk; or in transferring to the stone writings and drawings made with the pen or brush on transfer-paper, or impressions from copper, steel, and pewter plates, taken on a coated paper, and then in printing off from the stone the writings or draw ings thus made upon it. The principles of the art are these: an unctuous composition having been made to adhere to a calcareo-argillaceous stone, those parts covered by it— i.e., the writing or drawing—acquire the power of receiving printing-ink, whereas those parts not containing thc writing or drawing are prevented from receiving ink from the inking-roller by the interposition of water; and lastly, an absorbent paper being laid on the stone, and subjected to strong pressure, copies are obtained.
The best lithographic stones are found at Kelheim and Solenhofen, near Pappenheim, on the Danube, in Bavaria; but they have been found also in Silesia, England, France, Canada, and the West Indies. These stones are composed of lime, clay, and siliceous earth, and Etre of various hues, from a pale yellowish-white to a light buff, reddish, pearl-gray, light-gray, blue, and greenish color. Those of uniform color arc the best. The yellow-buff ones, being soft, are adapted for lettering and transfer; the pearl-gray ones, being harder, for chalk-drawings and engraving. They are found in beds, com mencing with layers of the thickness of paper, till they reach the dimensions of one and several inches in thickness, when they are easily cut, being yet soft in the quarries, to the sizes required for printing purposes. The stones are ground plane with sand, and, when required for the pen, the brush, the graver, or transfer, they are polished with pumice and water-of-Ayr stone; and for chalk-drawings and graduated tints, an artificial grain is given by ground glass or fine sand.
When any writing or drawing has been finished on stone, it then requires to be etched, thus: a mixture of 2 parts of nitric acid, and from 40 to 60 parts of dissolved gum arable, is poured over the stone once or several times, according to the nature of the work. The etching changes the surface of the stone, raising the work on it to a degree
scarcely perceptible to the naked eye. The writing or drawing, which has been effected by greasy ink or chalk, remains protected from the action of the acid, and those pro tected parts retain the natural property of the stone, which is the qualification of receiv ing printing-ink; and, when the printer wets the stone before applying the inking-roller, the water enters only those parts of the stone which have been affected by the acid. while the ink adheres only to those parts, however fine, on which the acid could not operate, owing to tbe unctuous composition of the ink or chalk with which the drawing or writing has been done, and which, being greasy, rejects the water. Thus it is called chemical printing.
The chemkal ink, for writings and drawings in line, is composed of 2 parts of white wax, 2 shellac, 1 hard soap, tallow, carbonate of soda, and 1 of powdered lamp, or better, Paris black. The chemical chalk (cmyon) is made of 3 parts of white wax, 2 hard soap, 1 shellac, 4- "drops of " mastic, 1 tallow, old lard, Venetian turpentine, I Brunswick black, carbonate of soda, and 1-1- of Paris black, properly melted and burned together.
When the drawing or writing with ink on a polished stone is completed, the etching is proceeded with, and a portion of the etching composition allowed to dry on the stone. The printer then adjusts his stone in the press, washes off the dried gum, removes the whole drawing or writing with turpentine, wets the stone with a sponge or damping canvas, then applies his roller containing the printing-ink, and rolls it several times over the stone till the lines appear again. When sufficient ink has been applied to the lines, the paper is laid on the stone, drawn through the press, and the impression effected. The damping and inking of the stone are renewed for every impression.