The Production Technology of, and Trade in, Egyptian Blue Pigment in the Roman World

Abstract

Egyptian blue was first used as a pigment on tomb paintings in Egypt from around 2300 BC, and during the subsequent 3,000 years, its use both as a pigment and in the production of small objects spread throughout the Near East and Eastern Mediterranean and to the limits of the Roman Empire. During the Roman period, Egyptian blue was distributed in the form of balls of pigment up to about 15mm across, and appears to have been the most common blue pigment to be used on wall paintings throughout the Empire. Egyptian blue was both the first synthetic pigment, and one of the first materials from antiquity to be examined by modern scientific methods. A small pot containing the pigment that was found during the excavations at Pompeii in 1814 was examined by Sir Humphrey Davy. Subsequently, x-ray diffraction analysis was used to identify the compound as the calcium-copper tetrasilicate C<sub>a</sub>C<sub>u</sub>Si<sub>4</sub>O<sub>10</sub>, and to establish that Egyptian blue and the rare natural mineral cuprorivaite are the same material. Examination of Egyptian blue samples in cross-section in a scanning electron microscope (SEM) revealed that they consist of an intimate mixture of Egyptian blue crystals (i.e. C<sub>a</sub>C<sub>u</sub>Si<sub>4</sub>O<sub>10</sub>) and partially reacted quartz particles together with varying amounts of glass phase (Tite, Bimson, and Cowell 1984). At this stage it should be emphasized that, in the literature, the term Egyptian blue tends to be used to describe both crystals of calcium-copper tetrasilicate and the bulk polycrystalline material that is used as the pigment and is sometimes referred to as frit. In this chapter, the suffix ‘crystal’ or ‘mineral’ will be added when the former meaning applies, and the suffix ‘pigment’, ‘sample’, or ‘frit’ will be added when the latter meaning applies. For the current study, a small group of Roman Egyptian blue samples were examined using scanning electron microscopy (SEM) with attached analytical facilities. Using the chemical compositions of the samples, together with the description of the manufacture of Egyptian blue given by Vitruvius (Morgan 1960) at the beginning of the first century BC in his Ten Books on Architecture, an attempt is made to identify the raw materials used in the production of Roman Egyptian blue.