Page 98 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Oxides and Hydroxides

CHAPTER 2

Let our next subject be ores, etc., of copper and bronze.. ..Antiquity
shows that the importance of bronze is as old as the city — the fact
that the third corporation established by King Numa was the Guild
of Coppersmiths.—PLINY THE E L D E R 1

D

uring the
the
metalwork,
corrosion of historic and
ancient
predominant oxide of copper to form is cuprite, Cu 2 0, a red suboxide of copper (cuprous oxide)
that occurs over a very wide range of conditions. In addition to being both a common mineral
and a common corrosion product of copper and copper alloys, cuprite is also an important col­
orant in ancient glasses. It has never found any obvious use as a pigment, however, because the
subfusc red color of ground cuprite could easily be obtained with natural ocher and sienna,
which were far more readily available than the pure mineral. The other, less common oxide of
copper is tenorite (cupric oxide), CuO. The hydroxide—spertiniite, Cu(OH) 2—may be a com­
mon intermediate product in many corrosion processes but is rarely isolated as a stable mineral
phase. Characteristics of these minerals are briefly described in TABLE 2.1.