IDENTIFICATION OF FORGERIES BY MEASURING TIN ISOTOPES IN CORRODED BRONZE OBJECTS

The reliable identification of fakes consisting of bronze often presents problems, because traditional methods such as stylistic studies, optical microscopy, chemical analysis or X-ray diffraction of the corrosion may not be conclusive. We present a method that is based on the comparison of the tin isotope ratios 122Sn/116Sn and 117Sn/119Sn in the metal and in the adherent corrosion layer. An artificial patina is usually generated within a short time period. It has been observed that such a procedure leads to a depletion of the light tin isotopes in the corrosion layer, while in naturally corroded authentic archaeological objects no isotopic fractionation has been detected. The method has also been applied to archaeological objects and it could be confirmed, among other examples, that the famous ‘Sky Disc of Nebra’ is authentic.