Nanoscale investigations of the corrosion of metallic artworks by X-ray Photoemission Spectroscopy

X-ray Photoemission Spectroscopy (XPS) is a surface-sensitive analytical technique commonly used in the field of materials science at the nanoscale level. Historically applied to the industrial field, it is also successfully used in the investigation of Cultural Heritage, both for diagnostics and for conservation purposes. The nature and the state of conservation of artefacts can be assessed by XPS surface analysis, evidencing the presence of efflorescence, patinas, degradation/corrosion products, coatings and protective layers applied in restoration treatments. The feasibility of probing the surface reactivity in the nanometric range and understanding the chemical processes, occurring in different aggressive environments, makes XPS a very powerful tool also in the field of Conservation of Cultural Heritage. This analytical technique can be very fruitfully employed for the validation of new eco-compatible conservation products (e.g. corrosion inhibitors for metallic artworks) and for the choice of the suitable conservation and restoration protocols. In this work, some case-studies related to the application of XPS to the conservation of copper-based and iron-based alloys artefacts are reported. In particular, the focus is on the evaluation of the conservation state and the identification of degradation phenomena of archaeological bronzes and on the assessment of naturally-derived corrosion inhibitors for a sustainable conservation of iron-based artworks.