Page 76 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

apparatus. As part of a United Nations initiative to evaluate atmospheric corrosion, various test­
ing sites have been set up across the world, including one established by the Getty Conservation
(
Institute GCi) in the Brentwood area of Los Angeles in 1997. The GCI site includes a United
Nations (U.N.) - approved testing rack for both sheltered and unsheltered exposure. The first set
of detailed U.N. reports was scheduled to be published after four years of exposure, in late 2001.

The indoor One of the most pervasive topics in art conservation at pres­
museum environment ent is the subject of the indoor museum environment. There is
not enough space here to review in detail all of the recent work
undertaken concerning the characterization of, the management of, and the problems associ­
ated with the museum environment. For metals, this environment is characterized by a range of
pollutants, relative humidity, and temperature problems that are not encountered in burial con­
texts, for example. These problems can result in the corrosion of metallic works of art, particu­
larly those made of lead, silver, or copper and its alloys.
Brimblecombe (1990) reviewed some of the relevant literature, which is summarized
in TABLE 1.6. The most common gaseous pollutants in museums are N O x , S0 2 , H 2 S, 0 3 ,
HCOOH, CH3COOH, and HCHO, all of which potentially interact with copper alloys, either
directly or as catalytic agents. The expected range of corrosion products is, therefore, nitrates,
sulfates, sulfides, oxides, formates, acetates, and salts of higher carboxylic acids; these are,
indeed, the kinds of products found in contaminated environments.
Emanations from display cases, furnishings, and other fabricated products in museums
may give rise to elevated levels of simple ketones, aldehydes, alcohols, esters, phenol, and tolu­
ene, in addition to the skin particles, fibers, and dust introduced by visitors. The principal prob­
lem with particulate matter is its deposition on metallic surfaces, followed by entrapment of
water vapor or the formation of localized higher humidity associated with the particles. This sit­
uation, coupled with particles that have a high-surface area and the presence of sulfate, chloride,
or other ions in some particulates, may increase corrosion. Localized increases in humidity on
metallic surfaces can initiate corrosion, which may result in greater deposition velocities for
particles at that site, and hence corrosion may be greatly accelerated. In display cases and stor­
age areas, the use of unsuitable fiber composites, wood, glues, foam, felts, fabric, rubber, paint,
sealants, or plastics is a continual problem because high levels of organic acids and aldehydes
can be released from them. Levels may reach the hundreds of parts per million, which are dam­
aging to art objects. Hydrogen sulfide levels are usually in the low parts per trillion level in the
indoor museum environment, but even parts per billion, which may be found in unsuitable dis­
play cabinets, can be very damaging especially to silver objects, as well as to copper and bronze.
The only recourse is to ensure that all materials used in display case construction and in storage
and display areas are tested for suitability.

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