Compositional and technological features of glazed pottery from Aosta Valley (Italy): a SEM-EDS investigation

Twelve finds of glazed pottery dating from the fourth to the seventh century AD excavated within the Aosta region (Italy) were investigated by scanning electron microscopy coupled with energy-dispersive X-ray detection (SEM-EDS). Analysis of ceramic bodies revealed, besides a general homogeneity in composition among the studied samples, the use of a noncalcareous clay for their manufacture; two shards stand out due to their high iron contents. Glazes proved to be high-lead products (more than 70% PbO in all of the samples investigated, but one). For one sample, a composition poorer in lead and richer in silicon, aluminium and iron was found. SEM observation of the interface between body and glaze suggests that the coatings were mostly obtained by single firing. A comparison between clay and glaze compositions suggests the use of a lead compound mixed with a silica-rich material and not a lead compound by itself.