Archaeometric and archaeological characterization of Medieval and post-Medieval tiles from S. Francesco’s church, Savona (Italy)

A set of ceramic materials - about 270 pieces, mainly consisting of bricks and tiles (terracotta and glazed ceramics) largely fragmented - was found during recent restorations under the flooring of a room overlooking the cloister of S. Francesco’s church in Savona. The fragments were dispersed in the filling between an airspace structure of bricks and the current floor. These loose materials form an unusual archaeological layer, whose precise chronological and stratigraphic data are lacking. However, as the history of the monastic building and of the examined room is rather complex and poorly known, the ceramic materials were analysed in order to acquire information on the architectonic phases through material data. At macroscopic scale the fragments showed typological and dimensional variability, thus were divided in groups with homogeneous characteristics. A representative sample of each group was analysed by optical microscopy (OM) and scanning electron microscopy (SEM) to obtain a full compositional and technological characterization. The analyses were aimed at identifying the provenance of the samples, and distinguishing different groups possibly to be related to different chronologies. Petrographic analyses of the fabrics allowed identifying the local production, as suggested by the presence of: gneiss and amphibolite inclusions to be related to the local Palaeozoic basement, and calcareous (foraminifera) and siliceous (diatoms, radiolarians, sponge spiculae) microfossils associated with the Pliocene marine sediments outcropping in the area of Savona. The presence, on the majority of the pieces, of the so-called graida (grid) a feature typical of the tile production of Savona (i.e., a sort of stamp on the back of the tile to ensure higher adhesion to the mortar), concurs with the geological markers in identifying as local provenance. The OM observations allowed inferring: firing temperatures of approximately between 800°- 900°C (partial decomposition of carbonates, partial vitrification of the clay matrix and dehydration of micas), and for the glazed tiles a good technical level (double firing, no residual inclusions or bubbles). Unfortunately the lack of data for uncoated terracotta tiles in the area of Savona made it difficult to find temporal constraints, e.g., through mensiochronological datasets. Only for some of the groups ante and post quem terms were established based on the correlation between the acquired dataset and bibliographical references. For example a group of green glazed square tiles has been dated to the end of XIII century, while a group of uncoated ceramics with a refined paste was dated to the XVI century based on archaeological evidences. On the whole, the study allowed organizing the findings, characterizing the manufacturing process (provenance and firing techniques), and formulating hypothesis on the temporal evolution of the flooring of the room (i.e., at least 3 different paving between XIII - XVI century).