Page 158 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

claringbullite, Cu 8 (OH) 1 4 Cl 2 -H 2 0, formed, but this was unstable under the laboratory condi­
tions and recrystallized to connellite within two days. (This synthesis is further discussed in
APPENDIX B, RECIPE 5.) Connellite occupies a stability field between the mineral phases bro­
chantite, malachite, and paratacamite, as shown in FIGURE 4.5. Pollard, Thomas, and Williams
(1990a) suggested that this should result in connellite being much more common as a corrosion
product on archaeological material than previously thought as a result of the substantial stabil­
ity field for connellite at pH 5-8 and a chloride ion activity equivalent to that of some natural
environments. A second stability diagram at a higher carbon dioxide concentration ( FI GURE 4.6 )
shows that the connellite stability region becomes very restricted compared with azurite at
higher pH values and with paratacamite at higher chloride ion activities. There are still very few
identifications published for connellite in the archaeological context. A recent identification was
i
made of this mineral, however, on an Egyptian bronze n the collections of the Fitzwilliam
Museum, Cambridge, England. The sample was submitted for analysis by Tennent as part of
research into the deterioration of bronzes and other objects in museum storage. The material
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was originally thought to represent an example of light blue corrosion products originating
from poor storage conditions, but the determination of connellite (Scott 1997b) shows that the
light blue material is part of the original corrosion encrustation from burial of the object.
The occurrence of connellite together with the copper trihydroxychlorides can be evidence
for crystallization in a saline environment, while other associations of connellite in mine depos­
its occur with both malachite and brochantite. Claringbullite, which has been found in mines
with cuprite, is very rare. Since it is probably unstable with respect to connellite, claringbullite
has yet to be identified on artifacts or paintings.

Calumetite The mysterious mineral calumetite, Cu (OH,Cl ) 2 · H 2 0 , makes
2
rare appearances from time to time. This exotic mineral was
first identified by Williams in 1963, together with the equally rare anthonyite (discussed in the
following section). Naumova, Pisareva, and Nechiporenko (1990) and Naumova and Pisareva
(1994) mention that calumetite has been found in fresco paintings and in paintings on canvas,
respectively. For example, small flakelike crystals of calumetite were found in eighteenth-
century frescoes at the Russian Solovetsky Monastery (commonly called "Solovki") on an island
in the White Sea, near the Arctic Circle. The particles examined may be a natural material rather
than a synthetic pigment. As with many of the basic copper chlorides, however, there is always
the suspicion that their presence could be explained by alteration of the original copper pig­
ment, such as malachite, due to chemical interactions with chloride ions. Nonetheless, calume­
tite has also been identified as a corrosion product on bronze antiquities. Meyers (1977) reported
the mineral in his study of the corrosion products on a bronze mirror in the Norbert Schimmel
Collection, New York, that dated to Egypt's Achaemenid dynasty (525-404 B.C.E.). 1 0 Helmi
and Iskander (i985) reported that calumetite occurred with atacamite, paratacamite, malachite,

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