Page 108 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

repeating the process several times until it is reduced to the color of cinnabar. 6 Cuprous oxide
was clearly being produced by this oxidation and washing process.
I MODERN ARTIFICIAL CUPRITE PATINAS Cuprite may be pres­
ent as an intentional patina on the surface of objects made of copper or bronze. The attractive
reddish brown patina is generally found in very thin layers. Formulas for such patinas are given
in Hughes and Rowe (1982). In addition to application for aesthetic purposes, deliberate oxi­
dation patinas have been used for conservation. For example, Socha and coworkers (i98o)
I
employed such a patina for the protection of the bronze column of King Sigismund II in War­
saw, as described in APPENDIX B, RECIPE 2. There is, of course, no guarantee that a new cuprite
patina will protect a bronze against further corrosion; alteration of the cuprite to a basic sulfate
or chloride may occur unless protective maintenance is provided.
I IMITATIVE CUPRITE PATINAS Pigments have been used in the
past to imitate cuprite patina on bronze objects, as is demonstrated by the gypsum-plaster mo-
dello for the shrine of Pope Benedict XV. 7 The white gypsum model had been painted green with
a terre verte, "green earth." Under the green layer, however, the plaster had first been covered
with occasional patches of brass gilding metal that had, in turn, been painted over with a red
ocher, closely simulating a cuprite patina. Finally, the green layer had been applied, presumably
to imitate the secondary green corrosion products of copper, such as malachite or brochantite,
with the red "cuprite" and occasional patches of a brassy metallic surface showing through.

Copper colorants in Reduced colloidal copper particles and red copper (I) oxide have
glasses and glazes been skillfully employed over the millennia to create beautiful
decorative effects in faience, glass, and ceramic glazes. 8 Copper
is a bright blue in an oxidized alkaline ceramic glaze but becomes greenish and may even turn
clear f the firing creates reducing conditions (Kingery and Vandiver 1986). In fact, the common
i
ceramic term copper green is used to describe the slightly bluish green color derived from using
copper salts; it is one of the principal ceramic colors.
In sanggam celadon ware, a variety of inlaid celadon developed in Korea in the thirteenth
century, the incised design is infilled with white or black slip, and additional decoration in cop­
per oxide glazes is used over the slipped decoration (Savage and Newman 1985).
I OPAQUE RED GLASS The opaque red glasses of antiquity have
generated considerable interest. When colored a deep red by cuprite, the material was some­
times called haematinum or haematinon glass and was used during the early Egyptian and Roman
periods for making enamels and mosaics as well as glassware.
Freestone (i987) examined examples of opaque red glass from Egypt and the Near East that
dated to the first and second millennia B.C.E. Some of the second-millennium examples from
the Near East are based on soda-lime-silica glass with no lead content and relatively high levels

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