[Gk. lithos, a stone; and graphein, to write.] The art of tracing letters, figures, and other designs on stone, and of transferring them to paper by impression. It was invented in 1796 by Alois Senefelder in Bavaria, where the most suitable stones are still quarried. The stone "is a kind of limestone, composed of lime, clay, and silica, usually of a gray color and of a very fine grain. The stones are round in layers varying in thickness, the thickness required for printing-stones being from 1 1/2 to 5 inches, according to size. They are ground face to face with sand and water, until the surface of both stones is perfectly level. After being carefully polished with a smooth polishing-stone they are ready for use. Writings or drawings may be made on the stone with a fine pen or brush, or drawn on paper having a specially prepared surface, and then transferred to the stone. The methods of printing, consisting of etching out the spaces between the lines of drawing with an acid, inking, etc., are too complicated to be here described. Chromo-lithographs are lithographs in which many colors are printed in one picture. As each color is printed from a separate stone, from three to thirty stones are often used to produce colored pictures.