The terracotta modelli of Palazzo Venezia in Rome: Investigation of the constituent materials for fundamental knowledge and to aid conservation decisions

Abstract

This work presents the results of the investigation carried out on a group of terracotta sculptures (modelli) (sixteenth to eighteenth century) belonging to the extraordinary collection of Palazzo Venezia in Rome. The study, the diagnostic analysis, and the conservation work, were possible thanks to the grant supplied by the Getty Foundation of Los Angeles and by the bank Intesa San Paolo. The terracotta modelli had a practical function as they were of great use as sketches to the creation of the final masterpieces or as models for restoration. As a consequence, the terracotta models allow reconstructing the creative process of artists and restorers, fundamental to outlining the ancient workshop production. X-ray fluorescence spectroscopy, micro-stratigraphic investigation, Fourier transform infrared spectroscopy, and micro-Raman spectroscopy were chosen as useful techniques to study the morphology and composition of the surface-painted layers. Usually the surfaces were painted in order to simulate the materials of the sculpture for which the model was created, for example lead white was used to obtain a white surface simulating marble. But, often the models were re-painted to make them more attractive for the antique trade. So, several pigments have been found on the surfaces such as zinc white, Prussian blue, chrome yellow, and mono-azo pigment. In some cases, the characterization of the surface paintings was particularly important to the final decision about removing or leaving the surface paint in place.