Page 408 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Needfor research Clearly there is a need for continued research on polymer coat­
ings and on methods to enhance their adherence to a metal sub­
strate, especially for both patinated and unpatinated bronze. This work should also take into
consideration recent industry advances in coating technology such as embedding nanoclusters
of copper in the polymer coating. The copper clusters act like "nanonails," anchoring the coat­
ing to the metal surface and forming stronger bonds than those created by other methods, such
as surface roughening (Menezes 1997).

P A S S I V E S T A B I L I Z A T I O N
Bronze artifacts can be stabilized without invasive chemical or mechanical treatments by
enclosing them in an environment that is oxygen free and with relative humidity strictly con­
trolled. Some of these approaches are briefly presented here.
It is possible to create a variety of oxygen-free environments to meet the needs of individ­
ual artifacts. Most of the systems are for dry objects, but even marine or waterlogged finds can
be stored in a closed container filled with an oxygen-free solution such as deaerated seawater or
dilute solutions of sodium sulfite.
Typically, an enclosed system uses an inert gas, such as nitrogen, for the storage of objects.
France-Lanord is credited with being the first to suggest this technique in the 1920s, and it is
now used for a variety of treatment options, from storage of unstable iron artifacts to anoxia
treatments for insect infestations in organic materials.
Simple systems make it possible to control the relative humidity in a storage environment,
which should be kept below 45% RH. A typical system would use small bags of silica gel placed
along with the object in a clear polyethylene container (a bag or box) with a tight-fitting lid or
airtight seal. A relative-humidity recording strip placed inside the clear box, facing outward,
can be read without opening the box. This type of enclosure can safely store bronze objects for
several months until the silica gel requires regeneration. The bronze objects can be regularly
i
inspected through the clear container, which makes them available for further treatment, f
required. In sophisticated museums, unstable bronzes are safely exhibited without further
treatment by enclosing them in display cases in which the relative humidity is controlled and
monitored regularly.
Vapor-phase inhibitors (substances that volatilize easily and permeate a closed container
with chemicals that retard corrosion) have been suggested from time to time for bronze storage,
but this is not a popular option because these compounds are often carcinogenic. They are
unlikely to be retained completely within small enclosures without risk to health from leaks,
permeation, and handling.

C O N S E R V A T I O N T R E A T M E N T S F O R B R O N Z E O B J E C T S
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