LITHOGRAPHY (STONE PRINTING) is a surface-printing process based on the principle that grease and water repel each other. The image is drawn onto a ground limestone plate (8 to 12 cm thick) with greasy crayon and/or Indian ink. The surface of the stone plate is then etched with a weak nitric acid. As a result of the acid's effect, the grease in the paint chemically joins with the stone, while in the areas without an image the acid enlarges the pores of the stone and makes its surface receptive to the effect of the water. The plate is then covered with gum arabic to produce a protective layer for the image. While making the print, printer's ink is applied onto moistened stone. The ink remains onto the image, while the surfaces without an image repel the ink because of the water. The printing is done with a special lithographic printing press, and the number of prints is unlimited.