Page 391 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott
P. 391
R E P A T I N A T I O N OF C L E A N E D S U R F A C E S
The repatination of cleaned surfaces is a reintegration technique that is often necessary with
corroded bronzes in the outdoor environment. Repatination may be limited to damaged areas
of the remaining patina, or it may be applied to the entire bronze sculpture, creating a new sur
face that hopefully will be maintained for the future. Repatination of an original bronze surface,
i
even f badly corroded and disfigured, is still a contentious issue because there is no certainty
that the treatment will improve the preservation of the bronze in the long term unless contin
ued maintenance is provided.
Outdoor bronzes Weil and coworkers maintained that most outdoor bronze
sculpture was intended to be bronze in color and polished (Weil
et al. 1982; Weil i985b) and that patinated or at least severely corroded bronze sculpture was best
restored to its original appearance. This point of view was exemplified by Weil's work on a
group of thirteen bronzes on the Washington monument by Thomas Crawford (1814-57)
and Randolph Rogers (1825-92) erected from 1844 to 1869 on the grounds of the state capítol in
Richmond, Virginia. Weil used a variety of repatination treatments to restore the sculptures to
the appearance they had when dedicated and first placed outdoors. Each bronze figure was first
heated, area by area, with a large blowtorch until any water present on the statue vaporized. The
patination mixture employed was the commonly used dilute solution of copper nitrate, ferric
nitrate, and potassium sulfide. This was applied in successive applications by brush or spray.
The surface was washed frequently to remove excess unreacted chemicals.
Weil also used the cold application of a patination solution called "French green," based on
ammonium chloride, creating a principally atacamite patina. This was followed by an applica
tion of dark pigmented wax whose surface appearance was modified by partial buffing to better
integrate the surface color and texture of the treated regions with the untreated surface. A coat
ing of Incralac (discussed under "Coatings for Copper Alloys") applied by spray could also be
used over this "French green" patina. This repatination solution was commonly used on later
French bronzes from the foundries of Barbedienne and Rudier, according to Weil (i985a).
In another example, the Museum of Art in Philadelphia cleaned the disfiguring surface lay
ers on a version of Rodin's The Thinker in 1992 using a poultice of disodium ethylene diamine
tetra-acetic acid (EDTA) mixed with cellulose powder. This complexing reagent is particularly
efficient, as are most chemical reagents, in removing cupric salts, but it attacks the cuprite layer
very slowly. Consequently, the outer corrosion layers on this sculpture were removed down to
a compact cuprite layer, which was then used as the base for chemical repatination using a solu
tion of ammonium chloride and potassium polysulfide. This was followed by hot waxing to pro
tect the new patina.
C H A P T E R T W E L V E
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