Glazed sgraffito ware from Torre Alemanna (Foggia, fifteenth to sixteenth century A.D.): technological aspects of a local production

Abstract

The archaeometric investigation of 46 potsherds of “Torre Alemanna type” pottery aimed to define a compositional reference group and to understand the technological characteristics of its production. Principal component analysis applied to bulk chemical data (XRF) of the ceramic body showed a strong compositional homogeneity. Their comparison with local clays and 6 fragments of bricks sampled from the ceramic kiln, on the one hand, revealed the use of alluvial clays as raw material and, on the other hand, proved their fractionation for the production of pottery. The mineralogical assemblages detected by X-ray powder diffraction analysis inferred maximum firing temperatures between 750 and 1000 °C for the ceramic body. Polarising optical microscopy and scanning electron microscopy with energy dispersive spectroscopy (SEM–EDS) investigations on coating revealed the presence of quartz-rich white engobe covered with a high lead transparent glaze. The polychromatic decoration was analysed by colorimetry and EDS to compare the colour characteristics through all the potsherds. A temperature range between 780 and 950 °C of liquidus temperatures was inferred from the ternary phase diagram of PbO-Al 2 O 3 -SiO 2 system. Overlap of temperature ranges for sintering of the ceramic body and maturing glaze points to a single firing of the Torre Alemanna type ware. The results obtained define the reference compositional group and technology of the Torre Alemanna type ware, already attested in several archaeological contexts of southern Italy, and showed a technological continuity with the past about the use of local carbonate-rich clays to produce fine pottery.

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