Ciro Ferri’s frescoes: a study of painting materials and technique by SEM-EDS microscopy, X-ray diffraction, micro FT-IR and photoluminescence spectroscopy

Abstract

Two mural paintings by Ciro Ferri from the second half of the XVII century that decorate the Saturn Room–Palatine Gallery–of Pitti Palace in Florence, have been investigated by optical and SEM-EDS microscopy, X-ray powder diffraction, micro FT-IR, photoluminescence and Mössbauer spectroscopy, in order to throw light on the painting technique, the original constituent materials (pigments and binders) and those employed in repaintings, and their state of conservation. The blue mantle of the king is of particular interest, painted by using smalt in fresco and then egg tempera of ultramarine blue. Smalt was found to have an anomalous discoloration, while the ultramarine blue pictorial layers were studied in order to understand the nature of the employed pigment (natural or artificial) and binders. Micro FT-IR and photoluminescence spectroscopies were particularly successful in the identification of the nature of this pigment, helping us in assessing whether the blue painting layers are original or not. These techniques applied to a series of ultramarine blue samples of well-known provenance, allowed us to propose specific markers. Micro FT-IR spectroscopy, applied directly to the sampled powders and fragments or to their solvent-soluble fractions, could be a fast and easy technique for the identification of organic binders, coatings and adhesives. Specific infrared bands can be used to identify the employed materials and/or as decay markers, rendering easier therefore a more appropriate description of the state of conservation of the investigated paintings.