Influence of natural patinas of outdoor quaternary bronzes on conservation treatment

The efficiency of the protective treatments applied on bronze patina has not been fully investigated yet with reference to the different rain exposures and the cleaning treatments. In this study, the influence of these two points on patina composition in a real outdoor bronze monument was investigated. The inhibiting efficiency of benzotriazole (BTA) was assessed on sheltered and unsheltered-like patinas obtained on synthetic quaternary bronze samples by specific accelerated ageing devices.The main results confirmed the structural differences between bronze patinas in sheltered and unsheltered areas (mainly in terms of Sn-species enrichment). They also revealed how the cleaning treatment impacts the bronze surfaces: on unsheltered areas it significantly enhances the surface enrichment in Sn-containing species. This differentiation, in turn, impacts on the conservation procedures, as shown by the lower protective efficiency of BTA measured for unsheltered-like patinas. This is due to the weak interaction between BTA molecules and Sn oxides.