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

Abstract 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. 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. The Parma baptistery samples contained amino acids indicating the presence of protein and oil. Pine resin was detected for the first time in the primer from the Ferrara cathedral panels. Raman analysis highlighted the presence of lead-tin yellow type I, orpiment, and novel decay products. Previous 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 on ancient polychromy is complex and requires sophisticated instrumentation to inform colour reconstructions. The results presented here are an extension of past diagnostic projects carried out between the 1970s and 90s, and support the re-examination of previous investigations. 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.