Page 386 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

because it removed chloride more effectively than water alone, although, as described earlier,
there would be the danger of patina alteration with this solution. The criticisms voiced about
total immersion methods were not addressed by Bertholon and coworkers; therefore, their
approach will probably not find many conservators using it as a practical treatment. The idea of
immersion and electrolytic treatment in pure water as published by France-Lanord in 1952 still
seems a more gentle approach to the dangers inherent in electrolytic treatment than this more
recent work, f immersion is going to be used at all.
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Goodburn-Brown (i996) tested different cleaning treatments on forty-five bronze Roman
coins to evaluate the degree of damage to microstructural detail preserved on their surface.
These bronze artifacts are from freshwater anoxic burial sites near the river Thames in Lon­
don, where many objects show remarkable surface preservation under copper sulfide crusts
(Goodburn-Brown 1997). This is not by any means a common occurrence n ancient buried
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bronzes. Fifteen coins were cleaned using glass-fiber brushes. Encrustations were removed from
another fifteen coins cleaned electrolytically in a 5% sodium carbonate solution. A steel anode
was used, and the current adjusted until a gentle stream of bubbles evolved from the coins. Each
coin was examined after 10 minutes, and none were cleaned for longer than 40 minutes. The
remaining fifteen coins were cleaned in a solution of 5% sodium diethylene triaminepentaacetic
acid (DTPA) with 0.5% Triton x-100, which is reputedly a biodegradable nonionic surfactant
(iso-octylphenoxypolyethoxyethanol). The most deleterious treatment was determined to be
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caused by cleaning with glass-fiber brushes, which left surface striations across the cleaned sur­
face. Neither the electrolytic nor the DTPA treatment destroyed microstructural detail; both of
them left a slight etching on the surface, but the end results were surprisingly acceptable. The
DTPA treatment is currently being used for surface cleaning of horological instruments at the
National Maritime Museum in Greenwich, England.

C L E A N I N G MARINE FINDS

Bronzes recovered from marine environments may be so thoroughly covered with concretions
that the entire surface is obscured. Marine finds can also be heavily contaminated with chloride
ions, and this contamination will have to be treated f the bronzes are to be stabilized against
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continuing corrosion. Therefore, removing marine concretions to reveal the object underneath
may require elaborate mechanical cleaning as well as chemical stabilization treatments. In some
cases, this may also involve removal of the patina of the bronze or dissolution of corrosion prod­
ucts. The aesthetic arguments in favor of nonstripping techniques have to be weighed against
the practicalities of dealing with marine finds.
The so-called Getty bronze athlete, which was extensively covered with concretions (see
PLATE 82), is an example of a famous marine find that was successfully treated. Although the
cleaning and the removal of core material by the private conservator was somewhat crude and
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