Portuguese tin-glazed earthenware from the 17th century. Part 2: A spectroscopic characterization of pigments, glazes and pastes of the three main production centers.

Sherds representative of the three Portuguese faience production centers of the 17th century - Lisbon, Coimbra and Vila Nova were studied with the use of mostly non-invasive spectroscopies, namely: ground state diffuse reflectance absorption (GSDR), micro-Raman, Fourier-transform infrared (FT-IR) and proton induced X-ray (PIXE) or X-ray fluorescence emission (XRF). X-ray diffraction (XRD) experiments were also performed. The obtained results evidence a clear similarity in the pastes of the pottery produced Vila Nova and some of the ceramic pastes from Lisbon, in accordance with documental sources that described the use of Lisbon clays by Vila Nova potters, at least since mid 17th century. Quartz and Gehlenite are the main components of the Lisbon's pastes, but differences between the ceramic pastes were detected pointing out to the use of several clay sources. The spectroscopic trend exhibited Coimbra's pottery is remarkably different, Quartz and Diopside being the major components of these pastes, enabling one to well define a pattern for these ceramic bodies. The blue pigment from the Lisbon samples is a cobalt oxide that exists in the silicate glassy matrix, which enables the formation of detectable cobalt silicate microcrystals in most productions of the second half of the 17th century. No micro-Raman cobalt blue signature could be detected in the Vila Nova and Coimbra blue glazes. This is in accordance with the lower kiln temperatures in these two production centers and with Co(2+) ions dispersed in the silicate matrix. In all cases the white glaze is obtained with the use of tin oxide. Hausmannite was detected as the manganese oxide mineral used to produce the purple glaze (wine color "vinoso") in Lisbon.