How Surface Analysis Can Contribute to an Understanding of the Preventive Conservation of Brass Instruments

Historical brass instruments can suffer corrosion during and after playing due to the high degree of humidity inside – but the surface chemistry inside the tuning slides remains essentially unknown. Based on a series of previously published works of the present authors, this paper describes in a comprehensive way how ex-situ xps surface analytical measurements can shed light on this topic. On freshly polished brass samples exposed to model solutions such as artificial saliva, a thick, polycrystalline surface film composed of copper-thiocyanate and zinc phosphate is formed, whereas in a phosphate buffer solution only a thin film composed of copper and zinc oxy-hydroxide and zinc phosphate is present. ‘As received’ brass samples from old instruments showed quite a thick surface film of copper and zinc oxy-hydroxide that protects the alloy beneath from corrosion. In combination with the in-situ electrochemical results, a first, tentative iden- tification of the surface film inside the tuning slides can be offered.