A diagnosis of the yellowing of the marble high reliefs and the black decorations in the chapel of the tomb of Saint Anthony (Padua, Italy)

This paper focuses on the chemical characterization of samples of black decorations and inscriptions, and of yellow-brown patinas collected from various panels of the ark from the chapel of Saint Anthony (Padua, Italy), using three analytical procedures based on gas chromatography/mass spectrometry (GC/MS). Analytical pyrolysis in the presence of hexamethyldisilazane followed by gas chromatographic-mass spectrometric analysis (Py-GC/MS) and two procedures based on gas chromatography/mass spectrometry after wet-chemical treatment of the samples (GC/MS) were chosen for the recognition of the organic substances (used originally or in the course of restoration) and of their degradation products. In terms of the two GC/MS procedures, one was used to characterize proteins, lipids, resins, waxes, bituminous materials and their degradation products, and the other to characterize saccharide materials. The three analytical procedures used enabled us to obtain information on the presence of egg proteins, lipid materials (beeswax, siccative oil and animal fatty material), saccharide materials and Pinaceae resin. Beeswax, animal fat, egg and saccharide materials have been used in the past as restoration materials, and pine resin and siccative oil were the main ingredients in the black decorations and inscriptions.