Polychrome sculptures of medieval Italian monuments: Study of the binding media and pigments

The Ferrara cathedral and Parma baptistery are exceptional medieval monuments and results of a technical study of the polychrome sculptures and reliefs are presented here. The results are an extension of past diagnostic projects carried out between the 1970s and 90s, and support the re-examination of previous investigations. Scientific and historical accounts describe medieval sculpted portals of European cathedrals as a prime example of the diffusion of the polychrome painting techniques. The technical study of paint fragments of ancient polichromy is complex and requires sophisticated instrumentation to inform colour reconstructions. In this study, micro-Raman classified pigments and gas chromatography mass spectrometry (GC/MS) identified the organic binding media on the pre-treated stone, primers, painted layers, and gilding. GC/MS analysis of samples from the Ferrara cathedral detected fatty acids that most closely match linseed oil and dehydroabeitic acid, a marker for pine resin, which was detected for the first time in the primer from the Ferrara cathedral panels. The Parma baptistery samples contained amino acids indicating the presence of protein and oil. Raman analysis added novel results on the pigments used, such as lead-tin yellow type I and orpiment, as well as on the state of conservation of paint layers. The data were also compared to a wide range of publications and were found to significantly contribute to the knowledge and research in architectural polychromy in the Romanesque-Gothic era.