Characterization of artificially produced copper and bronze patina by XPS

Miniaturized photoacoustic and photothermal sensors have been developed for non-destructive in situ control of the state of patinated copper and bronze monuments. For calibration purposes, various systematic surface and microanalytical studies have been carried out, including x-ray photoelectron spectroscopy (XPS) studies of artificially patinated copper and bronze substrates. In order to prevent patina sample damage by x-ray-induced reduction of cupric sulphates, it has been found necessary to perform XPS measurements at liquid nitrogen temperature. In this way reliable qualitative and semi-quantitative analyses of copper and bronze patina could be accomplished. The XPS analyses have been successful in detecting partial chemical transformations of patina films upon artificial weathering. The acid weathering procedure applied, which was thought to imitate a very aggressive industrial atmosphere with rapidly changing relative humidity, produced less basic cupric sulphates such as chalcanthite both in pure antlerite and brochantite films and in mixed patina films.