A metal plate is coated with a material called a ground. The artist then draws his design on the ground with a sharp needle, that cuts through the ground to the metal below. When the plate is put in an acid bath, these exposed areas will be etched (or eaten away). This produces the sunken line which will receive the ink. The artist etches on the plate those parts which will appear in the finished print as black or colored areas. Since the ground is soft, the artist is able to work more freely than is possible with engraving, displaying a freer, more relaxed quality of line. The length of time the plate is left in the acid bath (e.g. nitric acid or ferric chloride). will affect the darkness and character of the lines.
Etching prints are generally linear and often contain fine detail and contours. Lines can vary from smooth to sketchy. An etching is opposite of a woodcut in that the raised portions of an etching remain blank while the crevices hold ink.
Etching is part of the intaglio family (along with engraving, drypoint, mezzotint, and aquatint.) The process is believed to have been invented by Daniel Hopfer (circa 1470-1536) of Augsburg, Germany, who decorated armor in this way, and applied the method to printmaking. Etching soon came to challenge engraving as the most popular printmaking medium. Its great advantage was that, unlike engraving which requires special skill in metalworking, etching is relatively easy to learn for an artist trained in drawing