Page 280 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

Egyptian green Egyptian green is not as well known as Egyptian blue, but
the extent of its use as a pigment may be underrated. Schilling
(i988), for example, identified Egyptian green in the wall paintings of the tomb of Queen Nefer-
tari from about 1255 B.C.E. (PLATE 51). Schilling found that Egyptian green —rather than mala­
chite, as one would suppose — was used throughout the tomb to produce all of the green-colored
areas. Stulik, Porta, and Palet (1993) report microprobe data for Egyptian green that show the
green frit is much higher in silica content than Egyptian blue. Schilling was able to synthesize
the pigment under inert conditions by altering the ratio of starting components. According to
Wiedemann and Bayer (1982), Egyptian green will form in preference to blue f the iron content
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of the silica (from impurities in sand) is in excess of 0.5%.
I IDENTIFICATION AND MANUFACTURE Egyptian green was
first identified by Noll and Hängst in 1975. Two distinct varieties were found: a glass-rich pig­
ment with wollastonite as a minor phase and a wollastonite-rich pigment with glass and silica
as minor phases. The earliest occurrence of both types was found in Thebes in the Sixth Dynasty
tombs of Unas ankh (tomb no. 413) and of Khenti (tomb no. 405). El Goresy and coworkers
(1986) note that the starting mixture for the green pigment must have had a higher lime and
lower copper content than the mixture required to form Egyptian blue. Cassiterite was found in
the glass matrix of the wollastonite-bearing green pigment, although not as frequently as
in Egyptian blue samples; it was absent in all pigments from the Old and Middle Kingdoms.
Cassiterite was first identified in Egyptian green from the tomb of Thutmose IV (reigned 1400-
1390 B.C.E.) of the Eighteenth Dynasty, and its presence indicates that bronze filings or bronze
scrap may have been employed as a starting material for the pigment.
Egyptian green was invented during the Sixth Dynasty (2323-2150 B.C.E.), and the color
varies from olive green to blue green depending on the manufacturing technique (Ullrich 1987).
The concentrations of silicon, calcium, copper, and sodium in Egyptian green are quite varied.
The amount of copper oxide and calcium oxide, for example, can range from 2% to 10% by
weight, but not in a molar ratio of 1:1, which would favor the formation of Egyptian blue. Occa­
sionally, blue crystals are found within the green glassy pigment.
The manufacture of Egyptian green begins with making Egyptian blue, which, according
to Ullrich, starts with a mixture of quartz (in the form of sand); lime (either as limestone or
lime-containing sand); copper compounds (copper ores or bronze waste); and, as a flux, natu­
ral soda (natron) from Wadi Natrun in Lower Egypt. The ingredients are ground to a fine pow­
der and mixed in the ratio by weight of 5 quartz : 2 lime : 2 copper : 1 soda. After the mixture is
heated at 900 - 950 °C for 24 - 48 hours, a glassy blue mass develops with a high proportion of
Egyptian blue. f this mass is ground and fired again, the proportion of Egyptian blue increases
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further. f the temperature exceeds 1000 °C or f a reducing atmosphere exists, then a green frit
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