This article is the first in an occasional series of posts about printmaking techniques, this time we look at answering the common question "What is an etching?".
An etching is a print taken from a metal plate, usually copper. The design consists of lines "bitten" in to the plate by acid. When copper is placed in nitric acid it corrodes, but the acid will not harm wax or resinous substances. A ground of various mixtures is laid on the plate, and the etcher makes his design through this ground with a fine-pointed needle to expose the copper to the acid. Depending on the depth of line needed, the plate is left in the acid bath for a longer or shorter period. When a particular area of the plate is "bitten" enough, this area is coated with varnish and the acid thus prevented from further action. The plate is returned to the acid bath for deeper biting of the exposed copper, these "biting" and "stopping out" processes being repeated until the plate is judged ready for printing.
Printing is done under sufficient pressure to force the paper into the grooves cut by the needle to take up the ink: lines on an etching may often be felt with the fingers. Designs must be drawn on the plate in reverse to print correctly, and some masters of the art, such as Charles Meryon, used mirrors to copy accurately from their original sketches.