Nanoscale investigations of the degradation of metallic artefacts from underwater archaeology

Metallic artworks recovered from underwater archaeology represent an extremely valuable section of Cultural Heritage. Remarkable examples are archaeological Bronzes found in the Mediterranean Sea, such as the Riace's Bronzes and The Dancing Satyr. Archaeological metallic artefacts from marine sites presents some of the most difficult problems encountered by conservators. The evaluation of the conservation state and the identification of degradation phenomena of archaeological copper-based artefacts will be addressed in this work, since they may suffer from a pronounced and very dangerous electrochemical corrosion (also known as "bronze disease"). This post-burial degradation phenomenon is due to the ubiquitous presence of chlorine in seawater or in coastal marine environments that could induce the active cyclic copper corrosion and finally lead to the total consumption of the original alloy. Different analytical techniques can be fruitfully used in the investigation of metallic artworks. Among these, X-Ray photoemission spectroscopy (XPS) that probes the surface reactivity at the nanometric scale, is a very powerful tool for understanding the chemical processes that lead to the deterioration of the artwork in different aggressive environments.