Glazed graffita pottery from Torre Alemanna (Foggia, 15th–16th century AD): Technological aspects of a local production.

Torre Alemanna (FG, Italy) was one of the most important medieval example of Teutonic Knights Order life in Italy (13th-16th century AD). The archaeological excavations conducted by the Soprintendenza Archeologica della Puglia in 1999-2000 discovered and extracted a large number of glazed graffita potsherds dated to the 15th-16th century AD. This work presents the results of an archaeometric investigation of 46 potsherd of “Torre Alemanna type” pottery, aimed to define a compositional reference group and to understand the technological characteristics of its production. Principal component analysis and cluster analysis applied to bulk chemical data (XRF) of the ceramic body showed a strong compositional homogeneity. Local calcareous clay was used as raw material. The mineralogical assemblage detected by XRPD, inferred maximum firing temperatures between 800°C and 950°C. Optical microscopy and SEM/ EDS investigations on coating revealed the presence of quartz-rich white engobe covered with a leadbased transparent glaze. The polychromatic decoration applied on the engobe was analyzed by spectrophotometry (CIELAB) and EDS to compare the colour characteristics through all the potsherds. The microstructures observed at the boundary between the ceramic body and the surface coating point to a single firing to sinterise the body and to fix the coating. The results obtained show a technological continuity with the past about the use of local calcareous clay (Argille subappennine) to produce fine pottery, and define the reference compositional group of the “Torre Alemanna type” pottery, already attested in several archaeological contexts of Southern Italy