Page 153 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

TABLE 4.3 SELECTED THERMODYNAMIC DATA FOR SOME COPPER MINERALS

COMPOUND FORMULA A f C REFERENCE
nantokite CuCl - 2 8 . 2 Weast 1984
tenorite CuO - 3 0 . 4 Weast 1984
cupric chloride CuCl 2 - 4 9 . 2 Weast 1984
cuprite Cu 2 0 - 34.98 Weast 1984
covellite CuS -11. 7 Weast 1984
chalcocite Cu 2S - 2 0 . 6 Weast 1984
paratacamite Cu 2 (OH) 3 Cl -135. 3 Woods and Garrels 1986
atacamite Cu 2 (OH) 3 Cl -160. 1 Sharkey and Lewin 1971
botallackite Cu 2 (OH) 3 Cl -157. 9 Sharkey and Lewin 1971
malachite CuC0 3Cu(OH) 2 - 215.7 Symes and Kester 1984
brochantite Cu 4 S0 4 (OH) 6 -434. 5 Robie, Hemingway, and Fisher 1978
connellite Cu 19 (OH) 32 Cl 14 S0 4 -3H 2 0 -101. 3 Pollard, Thomas, and Williams 1990a
azurite 2CuC0 3Cu(OH) 2 - 343.3 Robie, Hemingway, and Fisher 1978
chalcanthite CuS0 4 -5H 2 0 - 449.3 Robie, Hemingway and Fisher 1978
anderite Cu 3 S0 4 (OH) 4 - 345.7 Woods and Garrels 1986
sampleite NaCaCu 5 (P0 4 ) 4 Cl-5H 2 0 -1512. 9 Pollard, Thomas, and Williams i 9 9 i
libethenite Cu 2 (P0 4 )(OH) -293. 7 Magalhaes, Pedrosa de Jesus, and Williams 1986
pseudomalachite Cu 5 (P0 4 ) 2 (OH) 4 - 678.8 Magalhaes, Pedrosa de Jesus, and Williams 1986
cornetite Cu 3 P0 4 (OH) 3 - 382.6 Magalhaes, Pedrosa de Jesus, and Williams 1986

Data are in cal/mol; to convert to SI units (kj/mol), multiply by 4.184.

Northern Wei dynasty (386-535) emperor at the close of the fifth century. Atacamite was
identified as a green pigment mixed with malachite and perhaps green earth in the polychromy
of cave 6. The atacamite particles were globular, rounded masses with a dark center, typical of
synthetic salts that have formed under conditions of alteration. The fact that this chloride was
found mixed with malachite leads to the suspicion that it is not an original pigment but an alter­
ation product of malachite. On the other hand, Piqué reports that atacamite is found in wall
paintings in the Dunhuang area from almost all dynasties, including the Northern Wei dynasty.
She refers to a report of a quarry for atacamite existing or having existed at Dunhuang, so the
question of alteration cannot be resolved without further research into the etiology of these pig­
ments. Proudfoot, Garland, and Larson (i988) mention observing "small rounded green par­
ticles" in pigment samples from two sculptures of the Tang dynasty (618- 907) and the Jin period

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