Lithography

Lithography (Greek lithos, “stone”; graphein, “to write”), process of printing developed in 1798 by the German map inspector Aloys Senefelder. Lithography involves a flat, lightweight, planographic surface on which the printing area is no higher than the nonprinting area; it depends for its action on the mutual repulsion of grease and water. Senefelder found that if a drawing were made on a flat piece of limestone with a greasy crayon, the lines would attract and hold an oily or greasy ink when the stone was wet, whereas other portions of the stone would take no ink. The drawing could then be reproduced on a piece of suitable paper rolled into contact with the stone.

In the 19th century lithography became the chief means of reproducing works of art and illustrating books and magazines; the French artist Honoré Daumier is particularly known for his many lithographs that gently satirize the social foibles of his day (See also Prints and Printmaking).

When the photographic preparation of plates was introduced, photolithography came into existence, as did offset lithography, when an extra rubber cylinder was used. They are both now generally considered methods of offset printing (see Printing Techniques). The rubber transfer cylinder runs in contact with the printing-plate cylinder, which has replaced the flat stone, and receives the inked image from it; this image is then offset onto the paper. The rubber cylinder keeps the delicate printing plate from coming in contact with the printed object. Very long printing runs, or periods when the plates are not changed, are thereby made possible, and the faithfulness of reproduction and sensitive shading, unique to lithography, are preserved.

Advanced lithographic techniques have become important in the field of modern electronics. Such techniques, which include optical, X-ray, and electron-beam lithography, are used in the microfabrication of integrated circuits and other semiconductor devices.