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.

Portuguese tin-glazed earthenware from the 17th century. Part 1: pigments and glazes characterization.

Two sherds representative of the Portuguese faience production of the first and second halves of the 17th century were studied carefully with the use of non-invasive spectroscopies, namely: Ground State Diffuse Reflectance Absorption (GSDR), micro-Raman, Fourier-Transform Infrared (FT-IR), Laser Induced Luminescence (LIL) and Proton Induced X-ray (PIXE). These results were compared with the ones obtained for a Chinese Ming porcelain, Wanli period (16th/beginning of the 17th centuries), which served as an influence for the initial Lisbon's faience production. By combining information of the different non-destructive spectroscopic techniques used in this work, it was possible to conclude that: Co(3)O(4) (Co II and Co III) can be found in the silicate matrix and is the blue pigment in the "Especieiro" sample (1st half of the 17th C.). Cobalt olivine silicate (Co(2)SiO(4), Co II only) was clearly identified as the blue pigment in "Aranhões" sample (2nd half of the 17th C.) - 824 cm(-1) band in the micro-Raman-spectrum. Cobalt aluminate (CoAl(2)O(4), Co II only) is the blue pigment in the Wanli plate - 203 and 512 cm(-1) bands in the micro-Raman spectrum. The blue pigment in the 1st half 17th century of Lisbon's production was obtained by addition of a cobalt ore in low concentrations, which gives no specific Raman signature, because of complete dissolution in the glass. However, in most cases of the 2nd half 17th century, the Raman signature was quite evident, from a cobalt silicate. These findings point to the use of higher temperature kilns in the second case.