Page 327 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

direction, and second-order straw color perpendicular to the slow direction, which indicates a
positive sign of elongation. The highly pronounced fibrous structure of trippkeite is very dif­
ferent from the structure of Scheele's green preparations. In addition, the color of the trippkeite
crystals is a pellucid turquoise when viewed macroscopically, whereas Scheele's green is an
entirely different color. Color-reflectance data for Scheele's green are shown in FIGURE 9.3A.
There is, therefore, no similarity whatever between these two substances, despite suggestions
that they might be closely related.
The commercial preparation of Scheele's green appears to have included a number of vari­
ants, such as the various greens known as Braunschweig green, Kaiser green, mountain green,
and Berg green. Some have various arsenic-to-copper ratios, depending on their method of man­
ufacture. In some cases, the pigment may actually constitute a copper acetoarsenite containing
calcium or barium sulfate (Mierzinski i88i).
Scheele's green may be used with water or oil, but the extent to which the pigment was used
in painting is obscure. By the i870s, Scheele's green was becoming replaced by Schweinfurt
green (also known as emerald green), which had better durability. Bomford and colleagues
(1990) mention the discovery of both Scheele's green and Schweinfurt green together with a yel­
low lake in the painting Music in the Tuileries Gardens by Edouard Manet (1832-83). Roy (1993)
found it in the I866 painting Queen Victoria at Osborne by Sir Edwin Henry Landseer (1802-73).
Scheele's green was also used as a colorant for wallpaper and fabrics, and in calico printing after
fixation with albumen. Parker (1812) even claimed that his preparation of the pigment could be
used to decorate coaches and building facades as well as to paint houses and ships.
I EMERALD GREEN Emerald green is a mixed copper acetate -
copper arsenite salt, Cu(CH 3 COO) 2 - 3Cu(As0 2 ) 2 , that was originally produced as a pigment in
Schweinfurt, Germany, in about 1814; hence its alternate name, Schweinfurt green. This pig­
ment was synthesized by Liebig (1823) and by industrialist Wilhelm Sattler, who, according to
Ultsch (1987), kept the process secret and built a lucrative business on the discovery from around
1814 to 1822. Liebig's preparation is as follows:

[ O ]ne part of verdigris is heated in a copper kettle with sufficient distilled vinegar to be dis­
solved, then one part of arsenious acid, dissolved in water, is added. The mixture of these
substances produces a dirty green precipitate, which is dissolved in a new quantity of vine­
gar. After boiling for some time, a new precipitate appears which is granular, crystalline,
and of a magnificent green. It is separated from the liquor, carefully washed and drained.
(Ultsch 1987:32)

There are essentially two routes for making the synthetic pigment—the acetate route and
the sulfate route—both of which demand considerable skill and knowledge to produce the best
quality product.

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