Lapis lazuli usage for blue decoration of polychrome painted glazed pottery: a recurrent technology during the Middle Ages in Apulia (Southern Italy)

Abstract

Seven fragments of atypical proto-majolica from the archaeological site of Siponto (Manfredonia, Foggia) were analysed by chemical and physical methods. All fragments have blue, brown and yellow painted decorations. Raman microscopy and Scanning Electron Microscopy–Energy Dispersed Spectroscopy (SEM–EDS) investigations identified the blue pigment to lapis lazuli. We previously identified this mineral in the blue coloration of the tin–lead glaze of proto-majolica finds at other Medieval sites in Apulia (Castel Fiorentino and Lucera). The discovery of the fragments from Siponto, in spite of their peculiar technological-decorative features, proves that the use of lapis lazuli as a ceramic pigment was not an isolated occurrence, but was quite common in the Middle Ages in the production of typologically heterogeneous ceramics in Southern Italy. To better define the scope of this use the composition of ceramic bodies was determined by Absorption Atomic Spectroscopy (AAS) and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). The results were compared with those from Castel Fiorentino and Lucera by multivariate statistical treatment. To identify the technological features of these atypical proto-majolica fragments, investigations were also carried out on the ceramic bulk, covering and decorations using Scanning Electron Microscopy–Energy Dispersed Spectroscopy (SEM–EDS) and Optical Microscopy (OM). Below the tin–lead glaze, characterized by a low tin content, a layer of clay material enriched in Ca and P was found that had been applied to obtain a white background for the painted decorations.