Page 331 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Emerald green was found on two works of art from the Vever Collection of the Freer Gal­
lery of Art: an Indian painting dating to about 1900 (Fitzhugh 1988) and a Japanese Ukiyo-e
painting by Hiroshige (i797-i858) (Fitzhugh 1979). Paul Gauguin (i848-i903) apparently
used emerald green in his work; his correspondence with the dealer Ambroise Vollard in 1902
shows his requesting that tubes of "vert Veronese" (emerald green) be sent to him in Tahiti
(Christensen 1993).
For a time, emerald green, under its alternate name of Paris green, was the favorite of
fakers and restorers of Chinese bronzes, and it was often employed to imitate the green cor­
rosion crusts of ancient bronzes (Gettens 1969). Paris green was also used extensively as an
insecticide, and by the time Beam was writing in 1923, its use as a pigment had been almost
completely abandoned. Large quantities of Paris green were still being exported from England
for use as a fungicide and for making antifouling paints for ships from the end of World War I
until the 1920s, but the pigment had to be handled with care because it was highly poisonous.
The so-called Tanalith process for treating materials against biological attack used Paris green
for this purpose.
Emerald green never attained great popularity as a pigment because of two shortcomings:
it is blackened by sulfurous pollutants in the atmosphere, and mixtures of this pigment with
cadmium yellow darkened rapidly due to sulfide formation (Fiedler and Bayard 1986). The Brit­
ish painter William Holman Hunt (1827-1910) refers to this kind of mixture as "a well-known
misalliance ...when put on, the tint was brighter than this at the side. It is now as it was within
two weeks of its first application—nearly black" (Hunt I880:491).
Fiedler and Bayard (1997) found that emerald green mixed with a cadmium yellow that had
a small sulfur content reacted immediately to form a dark brown substance when heated
slightly. The nominal reaction is:

4CdS + Cu(CH 3 COO) 2 -3Cu(As0 2 ) 2 = 4CuS + Cd(CH 3 COO) 2 + 3Cd(As0 2 ) 2 9.5

I OTHER GREEN PIGMENTS An unusual group of green pig­
ments known as green stannate of copper (Riffault, Vergnand, and Toussaint 1874) was consid­
ered the equal of the better-known arsenic greens, according to Gentele (1906). There are many
recipes for the preparation of this pigment group. One of them calls for a solution of 125 parts
of copper sulfate in water added to a solution of 59 parts of tin n nitric acid. The mixture is pre­
i
cipitated by adding sodium hydroxide, and the green product is washed and dried.
Other ingenious methods were devised for stabilizing a precipitated copper salt as a
pigment. For example, a pigment known as Eisner green was made in Germany, according
to Riffault, Vergnand, and Toussaint; although not as bright as Schweinfurt green, it provided a
serviceable color. Eisner green was made by pouring a decoction of yellow wood that had been
clarified with gelatin into a solution of copper sulfate, then adding from 10% to 12% tin dichlo-
ride. The mixture was then precipitated by adding an excess of potassium hydroxide, and the

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