Chemical and mineralogical characterization on glazes of ceramics from Coimbra (Portugal) from the sixteenth to nineteenth centuries

Abstract

Chemical, mineralogical and textural characterizations were performed on glazed pieces prepared in laboratory as well as on faiences fragments collected from the existing remains in “Santa Clara-a-Velha” monastery (Coimbra, Portugal). The chemical investigation was carried out using micro X-ray fluorescence (µ-EDXRF) and wavelength dispersive X-ray fluorescence (WDXRF); the mineralogical results using X-ray diffraction (XRD) and the textural profile was obtained by scanning electron microscopy coupled with an energy dispersive spectroscopy system (SEM-EDS). Attention has been drawn to the glaze mineralogical changes during the firing temperature process, where three different types of glazes were submitted to three different firing temperatures (800 °C, 900 °C and 1,000 °C). Under these conditions, it is possible to relate the mineralogical content of the fragments to their firing temperature. Furthermore, we focused our purposes on identifying the technological aspects of the ceramic production in Coimbra, such as the raw materials, manufacture techniques and firing temperature adopted for the glaze. The latter aspect is highly dependent on the ceramic materials. In the framework of a more general project, this survey has as premise the recognition of a pattern, which is thought to be exclusively typical from the region of Coimbra. The perspective developed in the present work is towards reliable archaeometric criteria, which can be used to characterise scientifically the ceramics from Coimbra.