New geochemical and Sr-Nd isotopic data on medieval plant ash-based glass: The glass collection from San Lorenzo in Carmignano (12th-14th centuries AD, Italy)

Complete and accurate chemical characterisation was performed on a repertoire of glass tableware and lightingware from San Lorenzo in Carmignano (Apulia, Italy). Twenty-three samples were investigated by scanning electron microscopy, electron microprobe analysis for major and minor elements, laser ablation inductively coupled plasma mass spectrometry for trace elements and thermal ionization mass spectrometry for Sr and Nd isotopic analyses. The research was aimed at improving the state-of-the-art knowledge on Apulian glass, especially on prunted beakers. Main results were: (a) two goblets were characterised as natron-based glass (one likely recycled, one of Egyptian provenance) and backdated to Late Antiquity; (b) the other twenty-one samples were made of plant ash-based glass, likely "fresh". Seventeen specimens were divided into three chemical groups based on their elemental and isotopic composition: 1) Prunted 1, compatible with Mediterranean glass (in particular, Syrian or Adriatic); 2) Prunted 2, compatible with either Mediterranean or Mesopotamian glass and 3) Prunted 3, using of a much purer silica source and compatible with Slovenian and North Adriatic prunted beakers, "blanchum" Venetian glass and some Levantine or Syrian glass. The hypothesis of Apulian workshops recycling preexisting materials was also put forward.