Page 385 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

results in further formation of basic copper chlorides, the treatment can be repeated. In the same
study, Rosenberg employed a local treatment consisting of 200 parts tin or zinc, or 150 parts alu­
minium powder, mixed with 8 parts of animal glue and 4 parts of glycerol dissolved in 10 parts
of hot water.
In an approach similar to Rosenberg's, zinc granules are added to a solution of sodium
hydroxide in which the object is then placed. Electrochemical reduction can then occur on
the surface of the object. Many student attempts to use this electrochemical reduction method
resulted either in irreparable damage to the patina, which was essentially stripped away from
the metallic substrate, or in the plating of zinc on the surface; the zinc then had to be removed
by further chemical treatment, such as boiling in sodium hydroxide solution.
Such treatments, making use of either overall or localized chemical reduction techniques,
were commonplace from 1920 to 1970 and highly damaging to the aesthetic and scientific inter­
ests of the object. Rosenberg's electrochemical reduction method, however, does not necessarily
imply that the patina as a whole will be stripped away. In fact, Madsen found that a problem­
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atic bronze object in Denmark that had been previously treated with 3% benzotriazole in etha-
nol continued to show evidence of bronze disease until Rosenberg's electrochemical reduction
method was tried. Following the use of this treatment, outbreaks of the disease were halted.
Another approach to the treatment of bronze disease that did not involve stripping away
the patina was investigated by France-Lanord (1952). With this electrolytic method, the object
was immersed in distilled water and became the cathode. It was connected by a wire to a milli-
ammeter and an anode of platinum or gold. The very low current passing between the elec­
trodes, due to chloride dissolution, was measured and plotted with time. When current flow
reached a plateau, the water was changed and the procedure repeated until no more current was
registered, indicating the washing out of most of the chlorides.
Although the methods proposed by Rosenberg and France-Lanord have much to commend
them compared with the more usual electrolytic stripping techniques, no recent appraisal of the
benefits of either method has been made. This is largely because of the danger of lack of control
over processes that involve immersing objects in gels or water followed by electrochemical
reduction, even f only affected parts of the object are treated; electrolytic desalination poses
i
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the same problem. At least in the United Kingdom and the United States, these methods appear
to have been largely overlooked in the past or ignored in preference to complete patina removal.
This is regrettable because much of the damage that occurred to bronzes in major museum
collections from 1900 to i960 could have been mitigated by using gentler techniques, such
as those of Rosenberg and France-Lanord, that were more sympathetic to the integrity of the
object and patina.
Twenty-five years after France-Lanord's work was originally described, Bertholon and
coworkers (1997) have, in effect, revived it by using electrolysis to remove chloride ions from
copper alloys. They chose, however, a 1% solution of sodium sesquicarbonate as the electrolyte

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