In-situ EIS characterization of outdoor corrosion behaviour of bronze and gilded bronze

Corrosion monitoring of bronze and gilded bronze artefacts exposed outdoors is an important issue helping to develop proper conservation strategies for our cultural her-itage. The corrosion process is particularly critical in the case of gilded bronzes be-cause the contact with the large cathodic gold surface galvanically stimulates the cor-rosion of bronze substrate at the flaws (pores and defects) of the gold layer. As a re-sult, an interlayer of corrosion products grows at the bronze/gold interface causing further damage and detachment of the gilded layer. In this research an in situ non-destructive EIS technique was adopted to monitor the corrosion rate process developed in the presence of synthetic rainwater on bronze and gilded bronze coupons produced with the ancient techniques adopted during the Renaissance period. The protectiveness of a silane coating against the corrosion of these substrates was also investigated. With this aim, a “contact probe” similar to that already used in the field of cultural heritage by other researchers was adopted for in situ measurements. The accelerated corrosion conditions applied to bare and coated bronze and gilded bronze involved wet & dry exposures to concentrated rainwater, producing with time a surface degradation representative of those actually developed during outdoor exposition of these materials.