Page 393 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott
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run and that, in any case, the sheen of the waxed surface that is commonly used as a protective
coating on bronzes of this kind would not be desirable in this particular case. Instead, he rec
ommended the use of a tinted shellac applied to the green areas to reduce the contrast between
the green and the black coloration. During the first conservation treatment, the sculpture was
given a diluted coating of Incralac. The appearance was not greatly improved, however, and the
bronze was retreated in 1992 with Arkon p-90, a fully saturated alicyclic hydrocarbon soluble
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in petroleum naphtha, used as a 15% solution. During the four years that the treated sculpture
was on exhibit, this coating became more plastic-looking and developed a slight milkiness. The
decision was made to re-treat the surface to try to achieve better reintegration. The Arkon p-90
was removed with Shellsol i, which was followed by cleaning with naphtha, but this failed to
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remove all of the coating. Xylene applied with cotton swabs finally succeeded in removing the
remaining coating.
A new treatment using Laropal aldehyde resin in mineral spirits was tried with good
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results, but it left too much surface gloss that would have necessitated matting out areas with
powder pigments. Most acrylic resins that were tried were also too glossy. Finally, tinted super-
blonde shellac was applied. This varied the opacity and finish of the resin to suit different areas
of the variegated surface (Bassett 1996); this is the finish that the sculpture now has.
In all these examples, any earlier patina still on the bronze after cleaning was allowed to
remain there when the sculpture was repatinated. There are, of course, conservation approaches
that involve totally stripping away an existing patina, using both chemical and mechanical tech
niques, before a new one is applied. This may be justified in particular cases, since every bronze
must be considered as an individual object with specific conservation requirements. There is no
universal panacea.
THE U S E OF C O R R O S I O N I N H I B I T O R S
A number of different organic compounds that complex with copper have been proposed as
corrosion inhibitors for ancient copper alloys or exposed bronze statuary. Corrosion inhibitors
act to retard the corrosion of metals by forming a stable surface complex that interferes with the
anodic reaction, the cathodic reaction, or both. In the case of copper alloys, complexes can also
be formed between benzotriazole and copper-corrosion products. The most well known com
pound is benzotriazole, which is reviewed here first and is followed by a brief account of other
corrosion inhibitors.
Benzotriazole In 1967 Madsen introduced the use of the corrosion inhibitor
benzotriazole (BTA) to conservation practice. In fact, benzotri
azole had been the subject of a British patent for use as a corrosion inhibitor in 1947 (Cotton and
Scholes 1967), and it had been used in commercial applications for twenty years before the
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conservation community became aware of its benefits for the stabilization of ancient bronzes.
C H A P T E R T W E L V E
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