Disclosing the composition of the Renaissance thin uniface metallic strikings by Alessandro Cesati (mid-16th century) from the Bargello Museum using non-invasive analyses

This study focuses on a series of thin uniface strikings preserved in the Bargello Museum (Florence, Italy), analysed using non-destructive and non-invasive techniques. These specimens were created in Rome by Italo-Greek sixteenth-century goldsmith and medalist Alessandro Cesati, called ‘Grechetto’, for Pope Paul III (1534–1549 A.D.) and Pope Julius III (1550–1555 A.D.). The samples were studied to explore the chemical composition and the surface morphology of the alloy since they are characterized by thin metal uniface strikings, representing a truly unique case study. New information about production technique, alloy composition, and on the use of these foils as prototypes by the artist are gained thanks to the analysis of such exemplars. A scanning electron microscope with an energy dispersive system (SEM-EDS) shows that the pieces are characterized by a surface enriched in Ag (up to 48 wt%) and/or Au (up to 6.3 wt%), whereas the back side shows an Sn-Pb alloy. In this specimen, Sn reaches 59.9 wt%, and Pb is up to 64.3 wt%, displaying a typical microstructure of Pb islands dispersed in an Sn matrix. Moreover, the absence of a preferential orientation of such lead clusters implies that the medal was subjected to very soft mechanical processing, such as hammering. FTIR analysis detected the use of a resin to glue the foils onto a different substrate, suggesting that Cesati also used these strikings to produce medallic prototypes to send to friends and patrons outside Rome.