The Medieval lead-glazed pottery from Nogara (north-east Italy):a multi-methodological study

摘要

The present work focuses on the archaeometric characterisation of 10th-11th-century lead-glazed pottery from Nogara (Verona, north-east Italy), with the main aim of defining the production technology of both glaze and clay body, through a multi-methodological approach. All the glazes, transparent and yellow to green in colour, are 20-100 um thick, texturally homogeneous and variable in composition, with high lead content (PbO: 53-76 wt%), variable silicon (SiO_2: 17-31 wt%), low aluminium (Al_2O_3: 4-7 wt%) and alkalis (Na_2O + K_2O: 0.6-1.7 wt%) and iron, acting as colourant (FeO about 2 wt%). The ceramic bodies are illitic non-calcareous clay-based, the textural features of which indicate neither depuration nor tempering, and firing temperatures generally under 850 °C. Microstructural, chemical and mineralogical evidence suggests that the Nogara glazes were produced by applying to the unfired ceramic body a lead compound flux, which caused partial melting and chemical diffusion phenomena in and outside the ceramic body. Small (<5 μm) newly-formed K-Pb feldspar crystallites, with euhedral morphologies, were also identified at the body-glaze interface of all samples, suggesting uniform firing techniques. The glaze colour, related to chromophorous FeO, must be considered as unintentional. Comparisons between Nogara samples with the same type of ceramics from various sites of the Mediterranean area and European countries, covering a wide time-span (Roman times to Modern age) show general chemical uniformity of the lead coating composition over the centuries, from whichever archaeological site the samples come. In addition, the results reported here further support the hypothesis that, in Italy, the tradition of using non-calcareous clay in combination with lead Compound by itself, appeared in late antiquity, continued until mid-Medieval times.