Natural and artificial ageing of protective coatings for outdoor bronzes protection

Any protective treatment for cultural heritage applications should fulfil specific requirements. Besides being transparent and colourless, they should be chemically and physically resistant to the degradation agents, possibly not toxic and removable without altering the underling patina and metallic substrate. For a better efficacy, protective coatings can be applied in association with corrosion inhibitors. A crucial issue in the evaluation of new products is related to their long-term performances. Typically, this aspect is investigated through accelerated ageing tests. However, these procedures seldom fully represent the complexity of real exposures. Thus, when possible despite the long time required, it is advisable to perform also natural ageing. This research was aimed to investigate and compare the long-term efficacy of traditional and innovative coatings for outdoor bronze surfaces. Coatings were applied in single, double and triple layer and in combination, through blend or pre-treatment, with corrosion inhibitors. The different treatments were applied on both patinated and non-patinated bronze specimens. The characterisation of the different treatments immediately after application was performed and reported on a previous work. [1] A multi-analytical approach was adopted for the study of the long-term behaviour of the different tested treatments, including colorimetric, SEM-EDX, FTIR, LPR and EIS measurements. Natural and artificial ageing have been compared in order to investigate whether the artificial ageing process could be considered representative of the real effect of outdoor exposure.