Winter 1990
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 accompl1shed 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.
Jim Hess, Associates Engraving, and and Paul F. Borth, IPA
