Abstract
The degradation of synthetic oil paint film specimens containing indigo and Prussian blue pigments and pictorial samples from the Sant Francesc de Paula painting from the museum of Cardedeu (Catalonia, Spain) has been studied by voltammetry of immobilized particles. This technique, combined with SEM-EDX, ATR-FTIR and CG-MS techniques permits to propose a dual scheme for the degradation of the pigments when submitted to natural, UV and UV solar light aging. Under ‘ordinary’ conditions, Prussian blue acts as a radical scavenger moderating the production of ROS produced in the binding media by the action of UV radiation, resulting in the formation of Berlin green and indigo adducts with radicals. In the case of localized areas of the Sant Francesc de Paula paint, strong degradation occurs where Prussian blue acts as a promoter of the indigo oxidation to isatin, thus resulting in a considerable chromatic shift.