Page 272 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

colla was valued by watercolor painters in the late sixteenth century. By the seventeenth
century however, it was already nearly forgotten (Harley i97o), and terre verte and synthetic
copper pigments were becoming popular substitutes.

D I O P T A S E
Dioptase, CuSi0 3 -H 2 0, a common silicate, is usually found as a massive vitreous green cluster,
associated with other copper mineral deposits, although individual crystals may also sometimes
be found. Dioptase can be a translucent, emerald-green color. The mineral is seldom used as
a gemstone, but small crystals have been emerald cut (Newman 1987), and some clusters have
been set in jewelry. The misnomer "copper emerald" is the name used for dioptase in the
jewelry trade.
Dioptase was one of the pigments — along with ocher, carbon black, and lime white — iden­
tified on a cache of lime plaster statuettes, approximately eight thousand years old, from the pre-
pottery Neolithic site of 'Ain Ghazal, Jordan (Tubb 1987). The dioptase was found in the eyeliner
on the statuettes, and this appears to be the only recorded use of this mineral as a pigment in
the ancient world, although there must be other examples that have not yet been reported in
the literature.

COPPER S I L I C A T E S AND G L A S S E S

Glass colored with copper salts or cobalt or both are of great antiquity in Babylonia and Egypt.
Partington (1935) mentions that glass-paste beads were found at Tell Mukayyar (ancient Ur),
dating from 3500 to 3000 B.C.E., and bluish paste beads were found at Lagash (ancient Telloh)
in Iraq. A fragment of blue glass from about 2400 B.C.E. that was found at Tell Abu Shahrain
(ancient Eridu) in Iraq is now in the collections of the British Museum. (Some information con­
cerning copper colorants is discussed in CHAPTER 2, under "Cuprite.")
Fine, dark blue Egyptian and Persian glazes were often imitated. In modern glass technol­
ogy, this degree of color saturation can be achieved only with cobalt additions, and it was often
assumed that the ancients also added cobalt to produce such an intense blue. This assumption,
however, is erroneous, according to Weyl (i98i). He points out that the use of cobalt ores in the
Near and Far East is of later date and that the Egyptians produced their blue glazes with only
copper and iron additions. Neumann and Kotyga (1925) found copper as a colorant in Egyptian
3
glasses from Tell el Amarna dating from 1400 B.C.E. All blue and green glasses of this period
contain copper oxide as the colorant. Finds from Aswan (an island in the Nile) included some
haematinon glasses (see CHAPTER 2) dating to around 1200 B.C.E. The outside of the glasses
were turquoise in color, probably due to the oxidation of the copper during molding, which
required repeated heating, according to Weyl. The behavior of copper in a silicate melt is not

C O P P E R S I L I C A T E S
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