Etching (derived from the Latin radere, to scratch, to scrape) is a printing method in which the ink-receptive indentations are not produced mechanically but chemically (etchings).
In this method a polished metal plate (copper or zinc) is covered by an acid-resistant layer (wax, mastic or asphalt) and is blackened with a fumigating candle, in order to render the design, which is to be applied, more visible. Then, the artist draws or scores the etch resisting layer with an etching needle, without penetrating the material. In the etching bath the acid then soaks into the lines created by the artist. Short or long etching times can influence etching depth.
In many cases the work is additionally treated by dry point technique afterwards. Then, the plate is cleaned, steel-plated for the printing process and inked. The ink then gets into the etching indentations. Afterwards the plate is cleaned so that the ink remains only inside the indentations. Then the artist presses a wettened print sheet (handmade paper) onto the plate.
Depending on the color desired, this process is repeated several times. For the Carborundum-Etching (a method developed by Antoni Tapies) the metal plate is covered, in the same way as is described above, by a mixture of polyester, gypsum, and other materials chosen by the artists, creating a thickly coated surface (the way it is done in a collage).
Additional printing inks can be applied, too. Then, in another printing process, the wettened paper is pressed onto these reliefs. In this way the sheets are given relief-like structures, an additional artistic feature.