A multi-analytical approach to unveiling raw materials and plaster recipes of Greek, Hellenistic and Roman fish-salting vats: The cetariae of Portopalo (Sicily, Italy)

The present study is focused on the compositional characterization of plasters from the ancient cetariae of Portopalo di Capo Passero in Sicily (South Italy) carried out in the framework of the ARCHEOFISH Italian-Spanish project undertaken by the Italian Istituto di Scienze per il Patrimonio Culturale (ISPC) del Consiglio Nazionale delle Ricerche (CNR), the University of Catania and the University of Cádiz. 22 samples were collected from the coatings of the vats used to produce salted fish and fermented fish sauces which, according to the archaeological investigations, belonged to different building phases at the site. The aim of the research was to characterize these materials and try to identify temporal and/or spatial variations. The analysis of plasters requires a multi-analytical approach involving analytical techniques providing both mineralogical-petrographic and chemical data. Specifically, optical microscopy with transmitted polarized light (OM), X-ray diffractometry on powders (XRPD), X-ray fluorescence (XRF), scanning electron microscopy coupled with microanalysis (SEM-EDS), and ion chromatography (IC) were employed. These analyses allowed to identify two main groups of samples distinguished by the presence of two different pozzolanic materials: artificial pozzolanic material or crushed ceramic fragments, named in this case cocciopesto, and natural pozzolanic materials or volcanic fragments. Furthermore, within the samples containing volcanic fragments, variations in the aggregates were observed, possibly reflecting different building phases. All the samples were studied with modal analysis and multivariate statistical analysis was applied. Additionally, differences in salt content among the vats were noted, potentially indicative of variations in fish processing methods. The analysis allowed the characterization of the building materials and confirmed the archaeological hypotheses on the presence of different building phases, providing innovative data on plasters from ancient food production installations from Hellenistic and Roman times.