Contribution de la diffraction de rayons X sous incidence rasante à l'étude de céramiques lustrées.

Abstract

The crystallographic structure of gilded archaeological (Fustat, Egypt, IX-XIth century) and contemporary (Grenade, Espagne) lustres, has been studied by X-ray diffraction. The classical Bragg - Brentano configuration and the grazing incidence with incident angles ranging from 0.5° to 10°, have been used. On such samples characterised by superposition of several complex layers, it was not possible to know exactly the depth analysed. Nevertheless, a simplified calculation based on the absorption of X-rays, shows that the minimal depth reached is nearly 85 nm. On the ancient glazes, cassitérite, diopside and quartz are identified ; on the modern glazes, only cassitérite is detected. In grazing the most intense metallic silver peak (111) is the only one noted on the ancient lustres. In one of these lustres, particularly enriched with copper, three metallic copper appear ; the existence of copper as oxides can not be asserted because of possible superpositions of peaks with cassitérite and quartz. On the contemporary lustres, the presence of metallic silver is confirmed by the two most intense peaks (111) and (200). These peaks are visibly widened. This fact reveals the presence of small metallic silver crystallites. The (200) peak, not disturbed by other phases, has enabled, by using the Scherrer formula, to calculate a size of silver crystallites of 15 nm.