Insights into Della Robbia's Terracotta Monument to Cardinal Federighi: Raw Materials and Technologies

The present work comprises the application of a multi-analytical strategy based on the combination of several non-destructive and micro-invasive methodologies for the examination of the glazed tiles from the tomb of Benozzo Federighi made by Luca della Robbia. The marble tomb is framed by flat glazed terracotta tiles, each ornamented with naturalistically depicted flowers. The tiles are assembled like an "opus sectile" and their background is gilded. The leaf is incorporated on the top of the glaze, differently by traditional gilding technique as in previous glazed works of della Robbia. The identification methodology integrates the results from spot analyses such as UV-vis reflectance spectroscopy and X-ray fluorescence, with those obtained on tiny samples by X-ray diffraction, electron microscopic observations, laser ablation inductively coupled plasma mass spectrometry and firing temperature analysis. The adopted analytical protocol allowed us to clarify peculiarities of the artist's technique and of the manufacturing technology used to create the terracotta and gilded glazed tiles. The terracotta body shows main phases related with Ca-rich ceramic body and the glaze results Pb-based and additioned with Sn as an opacifier. Co, Pb-Sb and Cu were identified as glazes colouring agents. The hypothesis on the use of the "third firing" technique for gilding tiles is explored in the text.