Examination of ‘Egyptian Blue’ by X-Ray Powder Photography

Abstract

X-RAY powder photography has been carried out upon various examples of the brilliant azure pigment known as ‘Egyptian Blue’. It has been found as early as the Fourth Dynasty (2900–2250 B.C.) and its use became very widespread throughout the Roman Empire. By this method crude frits from Tel-el-Yehoudi (Egypt), Silchester (Berkshire) and Woodeaton (Oxfordshire) have been shown to be of the same crystal form as a block already prepared for trading from Tel-el-Yehoudi, another in course of preparation from Armant (Egypt), and pale blue finely powdered pigment on pottery from Tel-el-Amarna (Egypt), and on wall plaster frescoes from Woodeaton. A potsherd from Woodeaton contained the same finely powdered pigment and was obviously used as a palette. All these examples were shown to contain essentially copper, calcium, and silica, with varying small amounts of sodium. Laurie and others¹ had previously shown that examples of a similar blue from Egypt, Rome, Knossos (Crete), Syria, and Wroxeter (Shropshire) consisted essentially of a definite compound—CuO.CaO.4SiO₂, which assumes this brilliant azure only if formed between 800°C. and 900°C.; outside these limits the frit passes to a green glassy mass.