Chemistry versus phase constitution of yellow ancient tile glazes: A non-destructive insight through XAS

Abstract

Using synchrotron radiation-based analytical (SRXRF) and spectroscopic (XAS) non-destructive techniques, a study was carried out on lead-rich, tin-opacified yellow glazes (silica-lime-alkali type glasses) decorating ancient tiles (17–19th century). These glasses have a rather complex chemistry, being currently assumed that the yellow pigment used for centuries – a pyrochlore-type double oxide of lead and antimony – prevails within the glaze, despite Sb(3+) being recognized as a net- work-forming cation in glasses. Minerals and synthetics with known crystal structure were used as model compounds to interpret X-ray absorption spectroscopy data at Sb K-edge and Pb L 3 -edge collected from ancient glazes. Theoretical modelling of Sb 1s XANES spectra was applied to demonstrate that antimony alone may be responsible for the yellow colour through a finely dispersed pyrochlore-type Sb-oxide, while lead remains hosted in the glassy matrix.