In situ conservation by cathodic protection of cast iron findings in marine environment

Nine cast iron cannons, dated between 17th and 18th century, were discovered in 2000 on the sea floor offshore the coast of the Marettimo Island (Sicily), scattered in an area of about 1200 square meters. The findings were left on the seabed, in the original place of their discovery, and a project for a marine archaeological park open to selected visitors was initiated by the Soprintendenza del Mare in collaboration with the Central Institute of Restoration. A comprehensive conservation plan was discussed among marine archeologists, conservators and materials engineers, aimed to identify efficient and non-invasive protection systems for the submerged cast iron objects. Cathodic protection was selected as the most interesting and promising conservation technique. Electrical protection of submerged steel components is a common practice for industrial or civil structures, that can be efficiently preserved circulating an external cathodic current on their surface using sacrificial anodes. In the case of components of artistic or historic relevance, particular care must be taken to guarantee the lowest impact on the object. Preliminary investigations concerning the materials and their conservation state (graphitization and corrosion potential), the position of the objects on the marine floor and the characteristics (temperature, pH, dissolved oxygen) of the environment were necessary. Zinc anodes were dimensioned and connected to the cannons by an original mounting structure.