Page 257 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Copper Phosphates and Copper Nitrates

CHAPTER 7

copper phosphates are not generally found as corrosion
products except in characteristic environments, primarily in association with buried bone and
in arid climates. Only one copper phosphate, pseudomalachite, has any history as a pigment.
The best known and most commonly occurring copper phosphate is turquoise, an ornamental
stone of various blue and green hues whose exploitation as a mineral can be traced back eight
millennia. Also discussed here are the relatively rare occurrences of copper nitrates.

T H E C O P P E R P H O S P H A T E S
The most common copper phosphate found as a corrosion product is libethenite,
Cu 2 (P0 4 )(OH), a vitreous, light-to-dark olive-green mineral often associated with bronzes
excavated from cremation sites. Photomicrographs of a sample of libethenite from the type site
of Libethan, Hungary, is shown in PLATE 44. Cornetite, Cu 3 (P0 4 )(OH) 3 , a vitreous or greenish