Ferric Chloride in Copper Etching

The etchant of choice for the production of intaglio and relief Images in copper has been, and is, ferne chloride, in aqueous solution. The metal-removal is accomplished by an oxidation-reduction reaction. with little or no evolution of heat or fumes. Etching may be done in a tray or in a machine that propels the solution against the plate by paddles or through spray nozzles. Alternately, the rate of reaction permits local etching by applying the solution to the plate surface with a swab or brush. A major problem in any etching operation which is intended to produce a well-defined image is that of “undercutting” or lateral etching. The image is generally defined by a photoprinted acid-resist, and the etching operation is expected to remove only metal not protected by that reSist. Chemical reactions normally proceed in all directions, thus the resist will normally be undercut by the etching process, and the remaining metal will not represent precisely the Image desired.