Page 279 - Copper and Bronze in Art: Corrosion, Colorants, Getty Museum Conservation, By David Scott

product is an undiluted, light blue color and soft f the alkali content is low; it is pale blue and
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hard f the alkali content is high. In another study of composition, firing atmospheres, and tem­
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peratures, Chase (1971) reached essentially the same conclusions as those arrived at by Tite.
Numerous small objects from the second half of the first millenium B.C.E. are made of fine­
grained frit to facilitate molding; consequently, these objects are a paler blue. Kaczmarczyk and
Hedges (i983) analyzed some Late Bronze Age fine-grained frits of Egyptian blue from Ras
Shamra (ancient Ugarit), Syria, and showed that both copper and bronze scrap were used as
starting materials for making the colorants. Moorey (1994) concluded that there is no distinction
in composition between the Syrian and Egyptian material for these frits.
I PIGMENT DEGRADATION A study by Green (1995) essentially
confirmed, once again, that Egyptian blue consists of cuprorivaite with copper wollastonite, sil­
ica, and a glass phase. Green analyzed a dark blue, almost black, sample of pigment on a papy­
rus that dated to 1300 B.C.E. and identified the pigment as Egyptian blue. Schiegel, Weiner,
and El Goresy (i989) reported that Egyptian blue can degrade and become devitrified, resulting
in a remnant phase of cuprorivaite that is a stronger blue than the original pigment. Mixtures
of Egyptian blue and orpiment were found by Schiegel, Weiner, and El Goresy on a late Ptole­
maic papyrus from the first century B.C.E. Polarizing light microscopy showed that many blue
particles had become discolored and the edges were brown. This deterioration may result from
the photochemical degradation of orpiment, which releases sulfur compounds. The group also
found that on several papyri, Egyptian blue and some green pigments had acquired a black
fringe, although the nature of the degradation was not reported in any further detail.
Green (1995) examined green pigments from two Egyptian coffins of the New Kingdom
(1100 B.C.E.) and the Late Dynastic period (200-100 B.C.E.) that may have been derived from
the deterioration of Egyptian blue. The pigments gave X-ray diffraction patterns consistent with
copper (II) wollastonite, though several were found to be mixtures of Egyptian blue with ataca­
mite. A pigment sample from a 1100 B.C.E. papyrus was identified as a mixture of Egyptian blue
with a green that was similar but not identical to malachite. When found on papyri, atacamite
appears to cause the material to become particularly fragile and brittle.
It may be difficult to correctly identify deteriorated samples of Egyptian blue pigment from
other copper minerals on objects in a burial context. Tite (i987), for example, notes that severe
weathering can leach out the bulk of the colorant as well as the alkali content, resulting in very
pale or white-colored frits. A very pale blue piece from Arpachiyah in Mesopotamia that was
thought to be an early example of deteriorated Egyptian blue frit proved on analysis to be a
sample of azurite.

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