Synchrotron radiation micro-XRD in the study of glaze technology

The production of glass represented an important technological achievement, and it was the starting point for the invention of a large variety of materials, produced by processes involving melting, partial or total, and precipitation of new crystalline compounds during cooling. In particular, those crystallites built-in the glaze due to partial or total insolubility of some elements originally present in the melt (for instance some colourants and opacifiers), as well as those crystallites formed in the glazes resulting from the interaction of the melt and the ceramic surface are subject of the highest interest in the study of glaze technology. Finally, devitrification and weathering gives rise to precipitation of new crystalline compounds closer to the surfaces and interfaces. SEM-EDX and WDX have been traditionally used to obtain the chemistry of the glazes and the identification of the crystalline compounds present. However, it has some limitations identifying minute crystallites (below 0.5 micrometers) and polymorphs, which are of the highest interest in the study of historical glazes. Synchrotron Radiation micro-X-ray Diffraction has a small beam size adequate to obtain the structural information of submicron crystalline compounds and high brilliance, optimal for determining the crystallites even when present in low amounts. In addition the spatial distribution of the crystalline compounds present in the glazes fundamental for the study of the interaction between the ceramic and the glaze may be easily obtained. The identification of the microcrystallites formed in the glazes and their distribution across the glazes gives direct information on trends of the technology of production, stability and weathering of ancient glazes. In this study a collection of Islamic glazes from the 9th to the 13th century AD from different origins and obtained with different raw materials and production routes are studied. Unreacted grains, reaction compounds, crystallisations and alteration compounds as well as their space distribution are obtaine