Page 122 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

aforesaid is to be washed, thus: having beaten it, cast it into a mortar, and having poured on
water rub it strongly with ye palm of thine hand against ye mortar, then having suffered it
to settle, strain it; and pouring on the other water, rub it again and do this by turns, till it
be pure and sincere. 2
Grinding, washing with water, and straining are essential steps in preparing many pig­
ments from natural mineral deposits, and the process has remained unchanged over the two
thousand years since Dioscorides' time.
In his Natural History, Pliny lumps together various green stones, including malachite,
under the umbrella "smaragdus." He refers to this word in a passage in which he describes stone
from Cyprus as the

chalcosmaragdus or copper smaragdus which is clouded by veins resembling copper.
Theophrastus records that in Egyptian records are to be found statements to the effect that
to one of the kings, a king of Babylon once sent as a gift a smaragdus measuring four cubits
in length and three in breadth. 3

This "copper smaragdus" from Cyprus is most probably an impressively banded malachite ore
of unusual attractiveness. Pliny also mentions that this copper smaragdus can be associated with
the color blue, and the only blue and green minerals of this type that are commonly found are
malachite and azurite. Some of Pliny's information is derived from On Stones, the fourth-
century B.c.E. Greek treatise by Theophrastus (372-287 B.C.E.). In writing about smaragdus,
Theophrastus (i956) mentions that the stones are easy to reach and occur primarily in the cop­
per mines of Cyprus and on the island lying off Chalcedon, an ancient city in Turkey. He adds,
"They are not often found large enough for a seal, but most of them are smaller in size; for this
reason the stone is used for soldering of gold, since it solders like chrysokolla." This "chryso-
kolla" was said to occur in native "kyanos," which is azurite, suggesting that in this case
"chrysokolla" probably refers to malachite.

Mineral properties Well-formed crystals of malachite are rare, and untwinned crys­
tals are practically unknown (Palache, Berman, and Frondel
1951). Crystal faces are often striated. The mineral is monoclinic and has a Mohs hardness of
3.5-4. Under the microscope, malachite particles may be a strong or weak green and often show
sharp internal and external angles due to cleavage planes. Larger particles are often fibrous
and pleochroic. The birefringence is high, allowing first-order red or second-order blue colors
to appear. The extinction is oblique or parallel and varies from distinct to undulóse (Mactaggart
and Mactaggart 1988).
As a corrosion product, malachite can occur in various forms: as rod-shaped crystals;
curved, fibrous crystals; botryoidal masses; fibrous aggregates; or bundles of tiny parallel fibers

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