Page 316 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

There are some published reports of copper-protein compounds being used in illuminated
manuscripts. Laurie (1914), for example, reports a grass-green, transparent, copper-containing
pigment in illuminated manuscripts from the eighth to the fourteenth century, and Flieder
(i968) mentions the same occurrence in illuminated manuscripts from the tenth to the fifteenth
century. These pigments were identified as copper proteinates. The GCI Museum Research Lab­
oratory was also able to identify a copper proteinate used as a dark green pigment, applied in
selective areas of design over verdigris, in the von Ems illuminated manuscript Barlaam und
Josaphat, which is discussed earlier. Evidence for the copper proteinate was derived from scan­
ning X-ray fluorescence microanalysis (Scott et al. 2001), which showed enhanced concen­
tration of copper in the dark green areas, and from the determination of the presence of pro­
tein by FTiR microscopy. 26 Analytical studies by gas chromatography-mass spectrometry
confirmed that the amino acid composition of this copper proteinate matched that of egg, vali­
dating the comments by Cennini concerning the use of egg mixtures with verdigris as a stable
manuscript pigment.
Roosen-Runge (i967) reports a glassy green paint that showed discrete particles of what was
assumed to be verdigris on manuscripts from the Middle Ages. More work is required to con­
firm the extent to which copper résinâtes or copper proteinates were actually used for illumi­
nating manuscripts.

O R G A N I C SALTS OF C O P P E R AND BRONZE C O R R O S I O N
Copper acetates can occur on bronze antiquities either as components of deliberate patinas pro­
duced by modern chemical techniques (Hughes and Rowe 1982) or as undesirable alteration
products due to poor storage conditions (Oddy 1975; Tennent and Baird 1992; Tennent et al.
1993). Some of the first cogent observations that display or storage can cause corrosion of bronze
objects was from work done at the British Museum (Werner 1972).

Corrosion problems in In the past, oak and mahogany were often used for the construc­
the museum environment tion of museum display or storage cabinets in England. Start­
ing in the early 1970s, however, the increasing price of timber
resulted in a host of new laminated plywoods and chipboard being used by museums. These
plywoods can release large amounts of acetic acid, formic acid, formaldehyde, and sulfides.
Fresh oak, in particular, produces unacceptable emanations of acetic acid, with concentrations
reaching as high as 50-200 ppm in a confined space. These new materials create a large num­
ber of problems for both conservators and curators, more so than old polished woods, many of
which are of the Victorian period, that are probably now dormant with little or no outgassing
of pollutants.

T H E O R G A N I C S A L T S O F C O P P E R
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