Page 329 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

from laboratory work (see APPENDIX D, TABLE 26); this is sufficient for identification. There is,
however, a finely detailed and more recent entry for copper acetate-arsenite (ICDD 31-448),
which renders the earlier entry obsolete. Fiedler and Bayard (1997) illustrate X-ray diffraction
data for emerald green pigment samples taken from Rocks at Belle Isle by Claude Monet (i840 -
1926) and from Follow the Arrow by Fernand Léger (188I-1955), both of which are in the collec­
tions of the Art Institute of Chicago. In APPENDIX D, TABLE 27, these data are compared with
data for copper acetate-arsenite. Curiously, neither of the pigment samples from the paintings
appears to have a major line at 9.71, but some examples of this pigment do. APPENDIX D,
TABLE 28, illustrates X-ray diffraction data from an emerald green (Schweinfurt green) pig­
ment taken from James Ensor's (i860-1949) seminal painting Christ's Entry into Brussels in 1889.
Painted in 1888, this work in the collections of the J. Paul Getty Museum is shown in PLATE 63.
The data for the pigment from the painting are a good match to the standard ICDD data for cop­
per acetate-arsenite (see APPENDIX D, TABLE 28) and also show that the pigment can retain good
stability over a one-hundred-year period.
Emerald green is a bright blue-green pigment, but the color varies depending on the
method of manufacture. This was evident from the laboratory syntheses: the pigment made
from the recipe derived from Beam (see APPENDIX B, RECIPE 27) was a brighter green than that
made using Gmelin's recipes (see APPENDIX B, RECIPES 28 and 29). The color-reflectance spec­
trum for emerald green in gum arabic is shown in FIGURE 9.3Β and is compared with that of
Scheele's green (see FIGURE 9.3 A) and of copper orthoarsenite, also in gum arabic, shown in
FIGURE 9.3c. Emerald green is lighter than Scheele's green, which is darker and duller, as seen
from the color coordinates in FIGURE 9.3 A. Particles of copper orthoarsenite are often micro­
scopically characteristic — consisting of small, rounded grains that are uniform in size — exhibit
a radial structure, and are strongly biréfringent. Some may have a pit or dark spot in the center
(Gettens and Stout 1966). PLATE 64 shows two photomicrographs of Schweinfurt green (emer­
ald green) from Ensor's painting; PLATE 65 shows a photomicrograph of Scheele's green.
Judging by the occurrences of emerald green listed by Fiedler and Bayard (1997), emer­
ald green was used primarily from the i830s to the early 1900 s, with many examples from
the Impressionist school. The pigment was identified by Townsend (1993) in Going to School,
a watercolor on paper from around 1832 by Joseph Mallord William Turner (1775-i85i) in
the Tate Gallery, London, and in Léger 's 1919 painting Follow the Arrow. An interesting occur­
rence of both emerald green and Scheele's green on Tibetan thang-ka paintings is mentioned by
Mehra (ΐ97θ), although exactly how the pigments were identified is not mentioned in the text.
Thang-ka is a popular form of religious painting on cloth done in the Himalayan regions of
Tibet, Nepal, Bhutan, and Sikkim. The need for these copper arsenate pigments in such areas is
surprising because the traditional green pigments used for thang-ka paintings have been verdi­
gris and malachite.

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