Method of engraving in which lines or textures are bitten, or etched, into a metal plate, usually copper, with acid. The image produced has a spontaneity of line that comes from drawing on the plate in the same direct way as with pen or pencil on paper. The first etchings date from the early 16th century, but the basic principle had been used earlier for the decoration of armour. Among the pioneers of the medium were Albrecht Altdorfer, Albrecht Dürer, and Parmigianino; the greatest of all etchers was Rembrandt. In the 20th century, etching was especially popular for book illustration. See alsoaquatint; engraving.