This process is best suited for creating tones rather than lines and is often used in conjunction with other intaglio techniques. The aquatint resist material is usually sprayed on the plate surface to act as a mask. The depth of tone is controlled by the thickness of the resist and by the length of time the plate is exposed to acid. Photo etching is an intaglio technique where an image is transferred to an etching plate photochemically. Afterward, the plate is immersed in acid to etch away only those areas where the opaque lines were located, leaving the rest of the plate unaffected.
Photogravure is a variation of the photo etching technique.
It involves overlaying a transparency image over a gravure emulsion tissue and then photosensitizing the tissue with a chemical solution until it becomes gelatinous. The degree of light striking the chemicals will cause the gelatin to harden in various thicknesses, becoming a varied acid-resist ground. The lightest areas in the transparency will produce the thickest ground that results in the lightest tones in the finished print. The etching and printing processes for these intaglio methods is too detailed to cover here, and more information should be gathered before attempting to work with this medium. With intaglio, a wide variation of images can be created either individually or by combining techniques.