Innovation and tradition in the fourth century mosaic of the Casa delle Bestie Ferite in Aquileia, Italy: archaeometric characterisation of the glass tesserae

The present paper focuses on the archaeometric characterisation of 38 glass tesserae of various colours from an in situ mosaic in Aquileia, Italy, dated to the second half of the fourth century AD. The examination of the textural, mineralogical and chemical features, conducted by means of a multi-methodological approach (optical microscopy (OM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), electron probe micro analysis (EPMA), X-ray diffraction (XRD) and Fibre Optic Reflectance Spectrophotometer (FORS)), has provided valuable insights into the changes in the production technology during the transition between the Roman and the Late Antique periods. The assemblage is heterogeneous, and each chromatic group is composed of tesserae produced with different base glasses and colouring/opacifying techniques, suggesting diverse supplies. A small group of tesserae shows strict links to the Roman tradition in terms of both base glass and colouring/ opacifying techniques and was probably obtained by re-using tesserae from older mosaics. Conversely, a larger group of tesserae shows textural and chemical evidence of recycling and indicates the prompt use of Bnew^ opacifying technologies (such as the use of tin compounds) or uncommon technological solutions (such as the use of quartz and bubbles as opacifiers or the addition of metallurgical slags in red tesserae), suggesting a specific production in the fourth century AD.