Page 276 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

fabricating it was brought there from Egypt by the now-obscure historical figure Vestorius. In
1815 Davy succeeded in synthesizing a blue frit. He writes:

[U]sing fifteen parts by weight of carbonate of soda, twenty parts of powdered opaque
flints, and three parts of copper filings strongly heated together for two hours, gave a sub­
stance of exactly the same tint, and of nearly the same degree of fusibility, and which, when
powdered, produced a fine deep sky blue. (Davy 1815:112)

Chaptal (1809) also carried out qualitative analyses of seven samples of the pigment from
the shops of traders in ancient Pompeii. Chaptal determined that the pigment was a frit of the
oxides of copper, calcium, and aluminum, which is not quite correct since alumina is usually
only a minor component.

Chemicalformulation Egyptian blue was identified as calcium copper tetrasilicate,
of Egyptian blue CaCuSi 4 O 10 , as early as 1889 by Fougue. It is interesting that
this synthetic pigment is, in fact, identical to a very rare natu­
rally occurring mineral, cuprorivaite, identified by Minguzzi (i938) from deposits at Mount
Vesuvius near Naples, Italy.
Egyptian blue is made by mixing quartz sand, calcium carbonate, and a copper compound
with a small quantity of alkali and firing the mixture between 900 °C and 1000 °C for several
hours. Both single and two-stage firing techniques were probably used; with the two-stage pro­
cess, the first product formed was ground up and retired, resulting in a finer-grained pigment.
The major component of Egyptian blue corresponds to cuprorivaite, but it is usually
accompanied by a copper-bearing compound that corresponds to wollastonite, (Ca,Cu)Si0 3 ,
and a glass phase enriched in the alkali elements sodium and potassium. Egyptian blue samples
from Old Kingdom sites, such as the tomb of Mereruka, Sixth Dynasty (2323-2150 B . C . E . ) , were
found by El Goresy and colleagues (i986) to consist mostly of cuprorivaite particles up to 200 μπι
in size, with minor amounts of wollastonite, glass, and tenorite. In contrast, the amount of the
glassy phase in pigments from the New Kingdom (ca. 1539-1075 B . C . E . ) is much higher, and the
texture is different. In these later pigments, cuprorivaite is idiomorphic to large subhedral crys­
tals in a glassy matrix, with wollastonite as very small crystals in the interstices of the cuprori­
vaite. El Goresy's group also suggested that a repeated, multistage process of regrinding and
sintering of the frit would be necessary to obtain such a high-grade pigment.
A typical sample of Egyptian blue pigment from a Canosa vase in the collections of the
J. Paul Getty Museum was examined by Scott and Schilling (1991). This ceramic funerary vessel,
shown in F I G U R E 8.2, was produced in southwestern Italy during the fourth to third century
B . C . E . and, like other vases of its type, was painted but not fired. The photomicrograph of the
Egyptian blue ( P L A T E 50) used on this Canosa vase illustrates the glassy particles, conchoidal

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