Evidence of early medieval soda ash glass in the archaeological site of San Genesio (Tuscany)

The early medieval period marks an important turning point in the history of glassmaking, since it comprises the transition period between the mineral-based silica-soda-lime glass of the Roman tradition and the plant ash-based glass. With the aim of expanding the knowledge on the glass recipes and technologies of this period, 37 glass samples were analyzed, originating from the archaeological excavations of San Genesio (Tuscany) and dated from the fourth to the eleventh century. The major and minor element concentrations were measured with SEM-EDX, while the trace elements were quantified with LA-ICP-MS. The results were compared with published compositions of glass samples of similar age in order to highlight differences and similarities. The results offer a very interesting view on the glass circulation in the religious/residential/manufacturing center of San Genesio in the early medieval period. Most of the glass has a typical late-Roman composition, but some glass fragments are identified as soda ash glass. These are among the earliest medieval ash-fluxed glasses ever found in the Italian peninsula.

► We have discovered the earliest medieval soda ash glass in Italy.
► Both natron glass and soda ash glass have been identified in the early medieval San Genesio, Tuscany.
► We have analyzed glass fragments that provide an interesting picture of an important transition period in glass history.
► 37 well dated early medieval glass fragments from San Genesio, Tuscany were analyzed with SEM-EDX and LA-ICP-MS.
► Medieval soda ash based glass appeared in Italy earlier (6–7th century) than previously reported.