Page 160 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

times, as long ago as 2000 B.C.E. During the reign of Pericles, from 460 to 429 B.C.E., the
Lávrion mines were intensively worked, producing many tons of discarded lead and silver slags
that have, over time, undergone further chemical alteration because of proximity to the sea. The
slags are rich in lead, silver, copper, iron, arsenic, antimony, vanadium, nickel, zinc, aluminum,
silicon, and sulfur. More than eighty minerals have been identified from the slags; among these
alteration products are cumengeite, boleite, pseudoboleite, and diaboleite, as well as atacamite,
paratacamite, botallackite, anthonyite, and calumetite.
Selwyn and coworkers (i996) identified yet another rare, mixed copper-lead chloride, chlor-
oxiphite, CuPb 3 Cl 2 0 2 (OH) 2 , from corrosion on a statue of Queen Victoria on Parliament Hill
in Ottawa. Unveiled in 1901, the statue was sculpted by Louis-Philippe Hébert (i850-i9i7) and
cast in Brussels at the J. Petermann foundry before being shipped to Canada. Analyses showed,
surprisingly, that the statue itself did not contain any lead, and Selwyn's group concluded that
the chloroxiphite had formed because of high local levels of lead pollution near the statue. The
source was most likely automobile exhaust during the period when gasoline still contained lead
additives, which were phased out in the 1980s.

Mixed copper-zinc chlorides In 1999 Stock found some mixed copper-zinc salts on the blis­
tered surfaces of reproduction Egyptian antiquities at the Royal
Ontario Museum. Data for a white efflorescence on an Ibis figure matched the data for a zinc
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sulfate chloride hydroxyl hydrate. A blue compound could not be positively identified, but it
contained major amounts of copper, zinc, and chlorine, with some sodium and lead. These
mixed copper-zinc chlorides probably originated from the artificial patination techniques used
on these objects.

Other mixed-cation A mixed cupro-ammonium salt was described by Clark (1998)
copper chlorides from the deterioration products on the cover glass over a pho­
tograph made by the wet collodion process. The print was
mounted in a gilt frame, and the glass was held together with a bent strip of decorative copper
foil. The deterioration products found on the glass included ammonium tetrachlorocuprate(II)
dihydrate, (NH 4 ) 2 CuCl 4 -2H 2 0, which was determined by Fourier transform infrared spec­
troscopy. Although an additional analytical method would be useful to confirm the identity
of this unique compound, there is no reason to doubt that mixed cupro-ammonium salts could
be present in a potentially wide array of different contexts. Undoubtedly, other mixed-cation
copper (II) chloride compounds await discovery and publication.

C H L O R I D E S AN D BASI C C H L O R I D E S
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