Page 19 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

F I G U R E 2 Native copper: A , typical dendritic
mass from the Great Lakes, : 5.8 cm;
L
1
B, photomicrograph, showing typical
microstructures, such as very long twin lines,
subtle banding within the twinned grains, or
regions of very fine precipitation; etched in
alcoholic ferric chloride (magnification
X I 8 0 ) . Since native copper is often formed
and shaped under very high stress, concen­
trations of strain lines can often be seen
undulating within the recrystallized grains
(Scott 1991) . Collection of the author.

Λ

environments, as well as the ancient and historical technologies developed for the manufacture
of colorants based on copper and its compounds.
Like many metals, copper is an essential element in our daily lives. An unusually good con­
ductor of electricity and heat, copper literally surrounds us in the form of copper pipes and elec­
trical wiring. Other copper products in common use today include copper cookware, decorative
fittings and fixtures, copper bracelets for arthritis, copper roofs, and copper-based coinage, as
well as copper compounds used as pigments and colorants for glass, special lubricants, and new
materials such as copper barium yttrium oxide, Cu 3 YBa 2 0 7 , and related compounds that are
gaining importance as superconductors (Nagano and Greenblatt 1988).
Copper may not be of paramount importance in industry now, yet it remains an essential
commodity, just as it is an essential element for biological life. Although copper is only present
0
overall at 70 ppm in the earth's crust and .001-0.02 ppm in seawater, the copper that is pres­
ent as a trace element in our bodies helps to catalyze hemoglobin formation; it transports oxy­
gen in the hemocyanin of blue-blooded mollusks and crustaceans (the same role that iron plays
in the hemoglobin of red-blooded animals) and is present in the ashes of seaweeds, in many sea
corals, and in the human liver.
The chemical symbol for copper is Cu, the element is number 29 in the periodic table, and
it has an atomic weight of 63.5. The atomic weight of copper is derived from the occurrence of
two natural isotopes, Cu and Cu, with relative natural abundances of 69.17% and 30.83%,
65
6 3
respectively. 2
A sample of dendritic native copper from the Great Lakes region of eastern North Amer­
ica is shown in FIGURE 2 A. The microstructure of some native copper, used millennia ago for

I N T R O D U C T I O N
2