On the conservation of easel paintings: evaluation of microbial contamination and artists materials

Easel paintings have been considered one of the most important art expressions, constituting today outstanding works of art with important historic and cultural value. Unfortunately, due to the presence of several organic materials, these artworks have been affected by microbial contamination that among other factors can be responsible for different aesthetic and structural alterations. For this study, four easel paintings from the late nineteenth century by Giorgio Marini with evident chromatic and structural alterations due to biocontamination were analysed in order to better understand the materials used and the source of high microbial contamination within a focused conservation intervention process. For this end, both the biofilms and the painting materials were characterised by several analytical techniques. Fungal communities were found to prevail in areas with evident structural and aesthetic damages, which were confirmed by scanning electron microscopy analyses that allowed the observation of the fungal hyphae proliferation capacity. Energy-dispersive X-ray spectroscopy, μ-X-ray diffraction, μ-Raman, μ-FTIR and optical microscopy were used to further identify the painting materials. Immunological assays revealed the presence of a mixture of proteins of ovalbumin, collagen and casein, suggesting that the presence of these proteinaceous materials in these paintings is one of the main reasons of microbial biofilms appearance on the painting’s surface. These approaches contribute for a better knowledge of these artworks providing at the same time relevant information for the ongoing conservation–restoration intervention.