Micro-Raman investigation of coloured glazes on majolica sherds from the Monk’s Palace waste shaft in Capena (Rome)

Medieval and Renaissance waste shafts (butti) offer a unique opportunity to study objects of common use in the past, the majority of findings that emerge from the excavation of these pits are pottery found in fragmentary condition, sherds that provide essential information on the historical periods to which the butto belongs. In the present work Micro-Raman analysis was conducted on a representative group of samples dated back from XIV to XVIII century, coming from the waste shaft pertained to the Monk’s Palace sited in Leprignano, the current Capena in the province of Rome. The aim of the study was to characterize the composition of coloured glazes pertaining to majolica sherds, through a technique that has proved to be invaluable for this purpose, according to the amount of published data in recent years. Differences in terms of structure and constituents of the decorative layers have been observed. Yellow pigments can be ascribed to the family of lead pyroantimonates, in both binary and ternary form, brown and green glazes are constituted by ions dissolved in the glass matrix, while in blue glazes cobalt olivines have been clearly identified for some samples. Polymerization index calculated on vitreous layers shows the presence of a lead-based glaze that is commonly found in majolica referable to the same age and provenance. The results obtained are in a good agreement with Piccolpasso’s treatise, “The Three Books of Potter's Art”, except for a sherd pertaining to a later Ligurian production.