Etching is a printmaking technique that uses chemical action to produce incised lines in a metal printing plate which then hold the applied ink and form the image. The plate, traditionally copper but now usually zinc, is prepared with an acid-resistant ground. Lines are drawn through the ground, exposing the metal. The plate is then immersed in acid and the exposed metal is ‘bitten’, producing incised lines. Stronger acid and longer exposure produce more deeply bitten lines. The resist is removed and ink applied to the sunken lines, but wiped from the surface. The plate is then placed against paper and passed through an printing press with great pressure to transfer the ink from the recessed lines. Sometimes ink may be left on the plate surface to provide a background tone.
Etching was used for decorating metal from the fourteenth century, but was probably not used for printmaking much before the early sixteenth century. Since then many etching techniques have been developed, which are often used in conjunction with each other: soft-ground etching uses a non-drying resist or ground, to produce softer lines; spit bite involves painting or splashing acid onto the plate; open bite in which areas of the plate are exposed to acid with no resist; photo-etching (also called photogravure or heliogravue) is produced by coating the printing plate with a light sensitive acid-resist ground and then exposing this to light to reproduce a photographic image. Foul biting results from accidental or unintentional erosion of the acid resist. Like engraving, etching is an intaglio technique. Intaglio refers to all printing and printmaking techniques that involve making indents or incisions into a plate or print surface which hold the ink when ink is applied to the surface and then wiped clean.