Characterization of Ethnographic Copper Corrosion

Analytical and electrochemical techniques were used to characterize the alteration of Tunisian ethnographic copper artefacts. Analytical results confirmed the existence of the bulk material in both objects constituting the ethnographic set. The bulk material was identified as a copper alloy with about 11% carbon content. The material was plated with a tin-based coating prior to use. Alteration characterization showed that corrosion is more severe at the bottom of the 'Kiskes' where the object was submitted to the hot steam. EN results reflected the interaction of the aggressive anion (Cl-) with the passive layer and the condensation of cation vacancies. Three anodic peaks were evidenced in the polarization curve corresponding to the oxidation of Sn(II), Cu(O) and Cu(I). A hysteresis loop was detected in the reversed scan confirming surface pitting.