Prediction of durability for outdoor exposed bronzes: Estimation of the corrosivity of the atmospheric environment of the Capitoline Hill in Rome

The evaluation and control of the durability of bronze monuments exposed outdoors in urban environments are urgent and technically complex topics. The possibility of predicting the behaviour of a metal artifact in contact with water and polluted air in particular climatic conditions is of fundamental interest for both corrosion scientists and conservators. In the present paper, the results of an investigation into the corrosivity of the atmosphere on the Capitoline Hill in Rome are summarized, evaluated on the basis of the mass loss results of standard metallic specimens exposed in situ. The use of the technique of polarization resistance is proposed for the objective evaluation of the real state of health of bronze sculptures in terms of actual rate of corrosion in progress on the metallic surface. Particular attention is paid to the results obtained for the Marcus Aurelius equestrian monument, exposed on this site for the past five centuries.