Chronological assessment of della Robbia sculptures by using PIXE, neutrons and luminescence techniques

Portuguese museums and private collectors gather a variety of Italian glazed terracotta sculptures attributed to the della Robbia workshop, particularly active between the 15th and 16th centuries. Compositional studies of the paste using INAA, PGAA and XRD and enamel using PIXE, and luminescence protocols, were used as a tool to ascertain the attribution of the sculptures to della Robbia workshop. Geochemical and mineralogical patterns were defined enabling to express the production recipe. The luminescence ages were found to be between 1380 and 1640 in some cases with high uncertainties. The compositions of the blue glazes were proved to be similar to other measured on della Robbia sculptures from French and Italian collections based on cobalt pigments. Arsenic behaviour, which is associated to cobalt in most cobalt-minerals, is rather peculiar, as it was already found in other della Robbia sculptures enabling a chronological framework, pointing to a production after 1520. Based on the results, most of the analysed sculptures implies a della Robbia production, and only a few point to a composition and chronology not related with that workshop.