Artistic and Laboratory Patinas on Copper and Bronze Surfaces

The study of characterisation and production of artificial patinas plays a key role in the field of cultural heritage. In particular, artistic patinas should be considered as an integral part of the artworks, as they are deliberately produced by artists and metalworkers as a part of their artistic design. Therefore, it is important to achieve a good knowledge of their composition and corrosion behaviour in order to setup and perform optimal conservation strategies for their preservation. In addition, the possibility of realising laboratory patinas that are as representative as possible of natural corrosion layers is important for the realisation of laboratory specimens which can be used as reliable model systems (mock-ups) for the study of degradation mechanisms and conservative treatments. For this work, both artistic and laboratory patinas have been considered and investigated. In particular, six different artistic patinas produced by Fonderia Artistica Battaglia were characterised. Moreover, a series of laboratory patinas was produced according to chemical procedures adapted from those already reported in the literature. The patina morphology was evaluated by stereomicroscopy observations, their composition was analysed by means of FTIR and XRD analysis and their corrosion behaviour was evaluated by LPR and EIS measurements. Finally, the LPR and EIS analysis have pointed out the low protection provided by the corrosion layers of artistic patinas. In regard to laboratory patinas, the optimized procedures of production were found to be effective for the realization of the main corrosion products of copper-based surfaces. From an electrochemical point of view in particular, quite different electrochemical behaviours were observed on artificial corrosion layers with the same chemical composition.