Lithograph

Lithography is a printing process based on immiscibility of oil and water. Artists draw or paint onto the surface of a limestone (traditionally stone but now usually aluminium) using a greasy crayon or liquid wash. A chemical solution is then applied over the surface, etching the portions of the surface that were not protected by the grease-based image. The printing surface is kept wet, so that a roller charged with oil-based ink can be rolled over the surface, and ink will only stick to the grease-receptive image area. Paper is then placed against the surface and the plate is run through a press. Each color requires its own stone and several subsequent runs through the press.