Page 22 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Evidence for the smelting of copper, in the form of primitive slags, has been found at such
Anatolian sites as Catal Hüyük, dating to the sixth millennium B.C.E. The deliberate or acciden­
tal smelting of copper ores with arsenic resulted in the first primitive versions of copper-arsenic
alloys with golden color and good hardening properties; some of these early alloys were perhaps
derived from the smelting of mixed copper-arsenic minerals such as olivenite, Cu 2 (As0 4 )(0H),
or clinoclase, Cu 3 (As0 4 )(OH) (Rapp 1986).
True alloys of copper with tin began to be made in the Old World from the fourth to the
third millennium B.C.E. and were pervasive and universal during the Bronze Age. Since tin is
found normally as cassiterite, Sn0 2 , however, the advent of tin bronze still holds many mys­
teries as to its sources and the development of knowledge needed to mine and extract the tin and
use it to alloy with different metals.

New World developments The use of native copper was common in the New World, espe­
cially in the period known as the Old Copper Culture of North
America, which lasted from about 3000 to 1000 B.C.E. and produced ornaments and axes
of native copper. Examination shows that New World metalworkers had discovered how to
work and anneal copper. The Hopewell Culture of Mound City, Ohio, is one of the best known
examples of these traditions.
Because native copper was especially plentiful in the New World, it was still being used dur­
ing the Christian era by the indigenous peoples of North America and Alaska from the time of
the Spanish conquest of the Americas in the fifteenth century onward. Only in South America,
however, did the cultural development make possible the smelting of copper, copper-arsenic
alloys, and later, tin bronze. The use of arsenical copper probably began in the first few centuries
B.C.E. in areas such as present-day Peru, with the knowledge of metallurgy spreading to other
regions at later dates.
True bronze alloys with tin were made in the New World during the early centuries CE.,
much later than corresponding developments in the Old World. The different timescales attest
to the independent development of copper metallurgy in the Americas. Tin bronze in the New
World is especially associated with Inca hegemony from the thirteenth to the fourteenth cen­
tury, but some antecedents are found n regions where tin was plentiful, as in present-day
i
Bolivia, Argentina, and Chile.

Development of brass Brass, the alloy of copper and zinc, was restricted in early usage,
because to smelt zinc, the temperature used must exceed the
boiling point of the metal. By co-smelting zinc and copper ores, brass did become impor­
tant during the Roman period, and the Romans produced brass coinage from 45 B.C.E. The early
history of developments in metal mining and production is the subject of a detailed review by
Craddock (1995); smelting and alloying are discussed by Tylecote (i976).

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