ARCHAEOMETRIC STUDY OF ROMAN MOSAIC TESSERAE FROM THE ARCHAEOLOGICAL AREA OF VILLA SAN PANCRAZIO (TAORMINA, ITALY): ED-XRF AND RAMAN SPECTROSCOPY ANALYSES FOR DATING AND MANUFACTURING ASSESSMENT

Villa San Pancrazio is one of the most extensive and significant archaeological areas of the city of Taormina (ancient Tauromenion / Tauromenium). The excavations in progress since 2015 are bringing to light a vast multi-layered Roman-Imperial residential quarter featuring luxurious dwellings decorated with wall paintings and mosaic floors. The present work deals with the study of tesserae sampled from polychrome and black and white mosaics, generally dated back to the Middle Imperial period, between the II-III century A.D. Mosaics are difficult to be precisely dated since stylistic and iconographic criteria are usually insufficient for a reliable chronological and manufacturing attribution [1]; thus this archaeometric investigation is meant to provide a scientific support for materials dating, by means of their identification as well as their production techniques assessment, that can also give some clues on the economic and cultural exchanges [2]. With this aim, a non-destructive multianalytical methodology, based on the combination of X-ray fluorescence by energy dispersive (ED-XRF), Raman spectroscopy and X-ray diffraction analysis (XRD), was used to characterize a wide selection of stone, ceramic and glass tesserae collected from the different mosaics. In addition, chemometric tools were used to extend the information about some raw materials origin and supply, by means of Principal Component Analysis (PCA) and class modeling tools. Soluble salts determinations by Ionic Chromatography (IC-HPLC) were also carried out to ascertain the conservation state of the buried samples. The investigations provide the establishment of the natural lithotypes used and how the artificial materials, i.e. ceramics, transparent and opaque glasses, were produced. The data comparison with the ones coming from other archaeological sites of the same age allowed the specific identification of coloring and opacifying agents applied, as for example, Co2+ and both the hexagonal CaSb2O6 and the orthorhombic Ca2Sb2O7 calcium antimonate phases in the opaque blue samples, respectively [3]. Data so far acquired allowed to ascertain the significant technical and qualitative level of the mosaic systems of the residences, thus confirming the high socio-economic profile of the owners. Preliminary results on soluble salts determination suggest that the tesserae are not involved in significant degradation phenomena.