Archaeometric Study of Islamic Potteries with Yellow Opaque Glaze Using Portable X-ray Instruments

Abstract

The characterization of Islamic yellow opaque glazed pottery excavated from the Raya site, Egypt, was carried out at an archeological site in Sinai, Egypt, using a portable X-ray fluorescence spectrometer and a portable X-ray powder diffractometer that we developed. The X-ray analyses revealed a cubic yellow pigment, Pb₂Sn_{2 − X}Sb_XO_6+X/2, in the yellow opaque glaze. This pigment formed a continuous solid solution with the replacement of tin by antimony. The calculated lattice constants from the powder diffraction data showed an increase in the cubic lattice constant as the Sn/Sb ratio increased. The X-ray powder diffraction pattern of the yellow pigment showed a strong preferred orientation parallel to the (111) plane. This phenomenon seemed to be caused by crystal growth of the yellow pigment, and may be related to weathering of the glaze. SEM-EDS analysis was carried out in our laboratory to study the weathering mechanism of the yellow opaque glazed pottery, using samples excavated at the Fustat site, Egypt, which are housed in a collection at Waseda University, Japan. The samples were analyzed to reveal the relationship between the chemical composition and the weathering of the glaze. It was found that if the base glaze is an alkali, the yellow glaze metamorphosed into a powdery state by weathering. In contrast, if the base glaze was lead, the yellow glaze became exfoliated from the clay body by weathering.