See also the work of Rembrandt and Picasso. Etching is an 'intaglio' process, which means that the lines and tonal areas of the image lie below the surface of a metal plate. The matrix is a metal plate, covered with an acid-resistant wax coating. The artist draws into the prepared plate, which is then immersed in acid. The acid 'bites' into the metal so when ink is applied to the plate, it remains in the incised lines.
Excess ink is wiped away, the plate is covered with paper and passed through the printing press.
The pressure transfers the inked image to the paper. Multi-colored etchings require a separate plate for each color. Again the matrix is a metal plate. In this case the artist works into the plate with a sharp metal needle. The needle is drawn with pressure directly across the metal plate, which raises a burr on either side of the incised line.