Survey of EIS measurements on copper and bronze patinas

This paper presents a survey of electrochemical impedance spectroscopy (EIS) measurements on copper and bronze patinas, both on coupons and on outdoor bronze monuments. Corrosion rates of the various patinas under examination show a wide range of values as can be guessed from the low frequency impedance modulus varying over two orders of magnitude. Similarities and differences between "historical" patinas and "short time" ones are sketched. Principal component analysis (PCA) is applied to EIS measurements on Monumento a Bartolomeo Colleoni bronze statue to enlighten data structure (i.e. groups and similarity between objects). In situ measurements of electrochemical properties of patinas, in conjunction with other analytical techniques, would provide useful information for better conservation practices.