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Lithography was invented c.1796 by Aloys Senefelder, and the Bavarian limestone he used is still considered the best material for art printing. Lithography is based on the antipathy of oil and water. A drawing is made in reverse on the ground (flat) surface of the stone with a crayon or ink that contains soap or grease. The image produced on the stone will accept printing ink and reject water. Once the grease in the ink has penetrated the stone, the drawing is washed off and the stone kept moist. It is then inked with a roller and printed on a lithographic press. As a process, lithography is probably the most unrestricted, allowing a wide range of tones and effects. Several hundred fine prints can be taken from a stone.
In color lithography or color photolithography, a stone or plate is required for each color used. The term photolithography is also applied to a process used in integrated circuit manufacture. Light is shined through the non-opaque portions of a pattern, or photo mask, onto a piece of specially coated silicon or other semiconductor material. The portions of the coating that were exposed to light harden, and the unhardened coating is removed, as by an acid bath. The uncovered silicon is altered to produce one layer of the integrated circuit. Advances in this technique have replaced visible and ultraviolet light frequencies with electron and X-ray beams, which permit smaller feature sizes in the patterns.