Page 80 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

nium sulfate particles is also an environmental concern, deposition rates have been mea­
sured outdoors as well, and they typically range from o.i to 1.00 cm/s. These data suggest that
increased rates of indoor airflow will cause greater deposition of pollutants on objects in muse­
ums without air-conditioning systems. Some air-conditioning systems in the United States are
equipped with filtration systems; for example, the one at the J. Paul Getty Museum uses acti­
vated charcoal filters that remove more than 95% of particulate matter.
I C O R R O S I V E M O L D S The potential for fungi of various kinds to
create corrosion problems was shown by Leidheiser (i979), who abstracted data showing that
molds grown in gelatin on the surface of brass plates caused rapid formation of deep pits; these
pits even occurred with molds commonly found in the atmosphere, although here such attack
is probably created by the diffusion of organic acids from the fungi to the metal surface dur­
ing bacterial growth. The most corrosive molds were Aspergillus niger, Aspergillus amstelodami,
Pénicillium cyclopium, Pénicillium brevicompactum, and Paecilomyees variotiBain. Molds produce
organic acids while growing on organic electrical insulation, varnishes, and varnished fabrics;
corrosion of copper, when in contact with such materials, can be extensive. Jones and Snow
(i965) found that after twelve hours of spore germination the following compounds were
present in distilled water surrounding the growth medium: alanine, asparagine, aspartic acid,
cysteine, cystine, ethionine, gamma-amino butyric acid, glutamic acid, glutamine, glycine, his-
tidine, hydroxyproline, leucine, methionine, phenylalanine, proline, serine, threonine, tyro­
sine, and valine. The corrosion of copper by these compounds, as well as by enzymatic agents,
was studied by Staffeldt and Calderón (i967). Infrared studies showed that organometallic com­
pounds of copper were formed in the presence of innumerable organic acids, even at an acid
concentration of 1% weight per volume (w/v). Acids studied were citric, fumaric, glutaric, ita-
conic, ketoglutaric, maleic, malic, oxalic, pyruvic, and succinic. All solutions turned green after
twenty-one days, except pyruvic acid solutions, which were yellow, indicating active corrosion.
I T R E A T M E N T R E S I D U E S Many corrosion problems are also

created by residues of old treatments, particularly salts that have not been completely rinsed off
the object; with fluctuating humidity or temperature, vestiges of these solutions may create
localized damage. Treatment solutions used in the past were either very alkaline or very acidic.
After a solution remains on a copper object for a prolonged period of time, their residues may
react with moisture and the object itself to form salts and create fresh outbreaks of corrosion on
the surface. Examples of such corroded objects in old museum storage areas are legion.
I T H E I M P O R T A N C E O F M O N I T O R I N G The ever-increasing rigor
and sophistication of monitoring techniques is essential to indoor air research, as a perusal of
the latest literature will reveal (see, for example, Del Bino 1997). This trend appears to be par­
ticularly active in Europe, and, like the National Acid Precipitation Program sponsored by the
National Science Foundation in the United States, the ongoing research can be expected to pro­
duce reams of data. Huge numbers of volatile organic compounds in the indoor environment

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