Etching, from the German word meaning “to eat,” is cutting into a surface of a material using acid. Etching is done on a variety of materials including glass, Plexiglas, and metal. Metal etching in particular is an industrial manufacturing technique, an art technique, and a technique for branding and identifying property. Etching was a technique used by many European artists including Albrecht Dürer, Francisco Goya, Rembrandt, and James A. McNeill Whistler to make prints before other processes gained favor.
In an art context, etching falls into the category of intaglio, along with other techniques such as aquatint, drypoint, engraving, and mezzotint. Daniel Hopfer and Urs Graf were early metal etchers, but Dürer is credited as responsible for the metal etching vogue of the sixteenth century when etching became an art form. Metal etching was first done on iron, but around 1540 copper etching began to predominate.
The method of etching on metal can be a chemical process using acid, a photochemical process, or an electrochemical process. The basic technique for acid metal etching is to apply a resist to the areas of a metal plate, either to the whole plate or just to the areas that one wants to remain unaffected. The parts of the metal to be etched are either not covered or the resist material is scratched off from them using tools such as an etching needle and an échoppe.
The metal plate is then dipped in acid which eats away the exposed surface of the metal, creating lines. To make a print, the resist is cleared away and the surface inked. When the surface is wiped, the ink remains in the etched lines and can then be captured on paper when put through a specialized printing press. Varying line depth is accomplished by removing the plate periodically and covering the lines that have reached the desired depth with the resist material. This can also be done by applying acid to the plate directly rather than bathing it.
Industrial metal etching is also called “chemical milling.” It is used in semiconductor fabrication, the printed circuit board industry, and in fashioning aircraft components by the aerospace industry. Photochemical etching is a variation on this process in which photolithograph is the method of creating the pattern. It is used in the art world by Ostrom Glass & Metal Works. Electrochemical etching was developed for the aerospace and automotive industries in the 1940s and is only recently expanding to uses in medical technology and use in art settings. It is used by artists such as Cedric Green.