A Review on Corrosion Mechanism of Archaeological Bronzes in Soil: from Noble Patina to Active Corrosion

This paper presents a review on corrosion mechanisms in archaeological bronzes buried in soil. The archaeological bronze objects show different corrosion mechanisms due to placing in different burial environments with various conditions and characteristics, by which various corrosion morphologies are observed in these objects. The main corrosion events in archaeological bronzes are occurrence of uniform corrosion with formation of noble patina and corrosion products such as oxides and basic carbonates of copper on the surface, and also active corrosion or bronze disease due to influence of chloride ions on copper and formation of basic copper chlorides. Furthermore, different environments lead to formation of different morphologies in archaeological bronzes that are called as type I and type II corrosion morphologies, which form under effecting of chloride ions amount in the soil environment. On the other hand, microbially influenced corrosion occurs in archaeological bronzes buried in anaerobic soils leading to formation of copper sulphide products. In order to explain these corrosion mechanisms in archaeological bronzes, some examples of studies on archaeological bronze objects from Iran are presented here.