Page 409 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

The Mitsubishi Gas Chemical Company recently marketed a container system that includes
a proprietary agent called RP that removes oxygen, moisture, and corrosive gases from sealed
containers. The object to be stored is enclosed in a plastic bag with low oxygen and moisture
permeability. Pouches of the RP reagent are added, and the bag is hermetically sealed. In less
than an hour, the moisture content can drop below 20% RH; in twenty-four hours, oxygen lev­
els can fall to below 0.1%; and after six hours, the concentrations of H 2 S, S0 2 , HCl, and N H 3
are less than 1 ppm. An oxygen indicator strip provides a ready confirmation of oxygen level.
The bag must be carefully selected for size appropriate to the object and may need to be spe­
cifically made by the conservator for the treatment at hand. The bag material should have low
permeability to oxygen and moisture. A ceramic-deposited film called ES CAL is exceptionally
good for this purpose and maintains the sealed environment for several years, whereas another
polymer film called PTS may suffice for only one year. Polymers based on nylon, polyethylene,
or polyvinylidene chloride are not suitable for containers. They all are highly permeable to both
oxygen and water vapor. As long as the oxygen indicator shows that the interior environment is
stable, corrosion of copper objects can be practically stalled using the Mitsubishi system.

N O N D E S T R U C T I V E T E S T I N G

Over the last thirty years, radiography has been used to assess the condition of antiquities, the
technology used in their manufacture, and their degree of mineralization. In recent years, Ital­
ian conservators have been especially active in the area of passive examination and monitoring
techniques. Marabelli (i987), for example, discusses the application of radiographic examina­
tion, ultrasonic testing, infrared imaging, and acoustic emission analysis to the examination of
sculpture. These techniques are briefly discussed here.

Radiographic examination Radiographic examination of an object can be carried out using
either a conventional X-ray tube or a gamma-ray source. An
X-ray tube uses an applied potential to generate X-rays, while a gamma-ray source makes use of
radioactive substances, which require constant shielding when not in use and are more difficult
to maintain and operate safely.
One of the first references to the use of radiographic techniques in conservation is that of
Gettens (1959), who perceived that by taking X-ray images of objects before treating them, it
would be possible to determine the existence and extent of any remaining metallic core. Beale
(i996) recounts Gettens's work on this topic, which dates from 1929, when he took corroded
bronzes from the Freer Gallery of Art in Washington, D.C., for radiographic study at a U.S. mili­
tary installation in Watertown, Massachusetts.
Although radiography has been useful for conservation studies, it should always be kept in
mind that it is not a strictly passive technique for imaging hollow bronze sculpture. Any core

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