type of printing plate developed in the late 18th century and widely used in letterpress, newspaper, and other high-speed press runs. Stereotypes are made by locking the type columns, illustration plates, and advertising plates of a complete newspaper page in a form and molding a matrix, or mat, of papier-mâché or similar material to it; the dried mat is used as a mold to cast the stereotype from hot metal. A stereotype plate is much stronger and more durable under the press run than would be the composed page of type. It is gradually being replaced, however, by photopolymer (photosensitive plastic) and lithographic plates.