Page 164 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

The use of copper sulfate compounds in medicine was also well known in Greek and
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Roman times. Around 150 E . , Galen of Pergamum (129-ca. 199 E . ) , a noted Greek physician
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and scientist, made several journeys to Cyprus specifically to obtain fine mineral specimens of
copper and iron salts (Koucky and Steinberg 1982 a,b; Walsh 1929; Galen 1928). These visits pro­
vided Galen with enough material for more than thirty years of research. The Greek scientist
describes how he collected different samples from three layers at the Skouriotissa mine: from
the lowest layer he obtained "sory"; from the next layer, "chalcitis," and from the highest layer,
"misy." When he examined some of the chalcitis twenty years later, he found that it had formed
an encrustation of misy. Writers in the mid-sixteenth century, including the Saxon physician
and theologian Johann Agrícola (1494-1566), made reference to the same naturally occurring
copper salts as well as to others, including "melanteria" and "atramentum" (or "atramentum
sutorium"). 6
Misy, a golden yellow mineral, is probably copiapite, Fe 5 (SO 4 ) 6 (OH) 2 -20H 2 O, or meta-
voltine, (K,Na,Fe) 5 Fe 3 (S0 4 ) 6 (OH) · H 2 0 . Chalcitis ("chalcanthum") may refer to chalcanthite,
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CuS0 4 -5H 2 0;topisanite, (Fe,Cu)S0 4 -7H 2 0; ortoromerite (Fe,Cu) 3 (S0 4 ) 4 -14H 2 0. Both sory
and melanteria are basic copper-iron sulfates such as melanterite (Fe,Cu,Zn)S0 4 -7H 2 0. The
identity of atramentum (or atramentum sutorium) varies, according to Bandy and Bandy (1955),
from melanterite to chalcanthite.

THE B A S I C C O P P E R S U L F A T E S
Today the basic copper sulfates are of interest as corrosion products that have formed on bronze
statuary exposed in the outdoor environment for long periods of time. More attention is being
given to this type of corrosion as efforts are made to ensure the long-term preservation of these
works of art. Some pioneering work was done in Germany during the nineteenth century and
in England in the 1920s, but practically all useful research on the subject of copper sulfate cor­
rosion has been carried out since i960.
The most important basic sulfates that tend to form during outdoor corrosion are brochan­
tite, CuS0 4 -3Cu(OH) 2 or Cu 4 S0 4 (OH) 6 ; anderite, CuS0 4 -2Cu(OH) 2 or Cu 3 S0 4 (OH) 4 ; and,
to a lesser extent, posnjakite, Cu 4 S0 4 (OH) 6 -H 2 0. Other, less common sulfates are also dis­
cussed in this chapter. Characteristics of these compounds are shown in TABLE 5.1.

Brochantite and antlerite Brochantite is the most stable and usual corrosion product to
form on copper alloys exposed to the atmosphere. Since the sta­
bility and existence of brochantite as the most stable mineral phase in the patina of exposed
bronzes is not in question, the discussion here focuses on the relationship between antlerite and
brochantite and the mode of formation of the basic sulfates. De Gouvernain (i875) made an early

BASI C S U L F A T E S
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