Study and dating of medieval ceramic tiles by analysis of enamels with atomic absorption spectroscopy, X-ray fluorescence and electron probe microanalysis

This paper reports an analytical study of enamel on fragments of medieval tiles using atomic spectroscopy techniques — AAS, XRF and SEM/EDX. The samples came from a hermitage in the region of Valencia (Spain) and have different motifs, mainly floral ones in a wide variety of colors. A study of the soluble salts in the biscuits and mortar was carried out using AAS to determine their present capacity to produce efflorescence and the type of efflorescence. XRF was used to identify the oxides responsible for the different colors and the pigments used over large areas of the tiles (white and green). SEM/EDX was used to characterize the white and green and smaller areas of other colors. A correspondence between the different colors and tones and the metallic elements or mixtures was established. X-Ray energy spectra obtained for different areas of the same color have made it possible to quantify the contents of different elements, and thus to study the homogeneity of application. The presence of zinc is justified because of the physical and chemical properties it imparts to the enamels. The complementary nature of these spectroscopic techniques have made it possible to evaluate the state of conservation, to establish measures to clean the existing efflorescence according to their nature and to suggest dating of the materials.