Abstract
Nowadays, understanding the degradation processes of artworks exposed to outdoor conditions is essential in order to conserve these objects. In fact, the continuous climate changes risk to increasingly affecting their chemical-physical stability, especially for modern and contemporary ones. For this purpose, in this study, the kinetics of photo-oxidation processes occurring in synthetic binders and their stability in mixtures with different inorganic pigments were investigated. The aim was not only to characterize the different degradation reactions over time but to study the photodegradation kinetics according to the different pigments and pigment/binder ratio (P/BM) chosen. A total of 9 paint samples were prepared by mixing the inorganic pigments (artificial ultramarine blue, hydrated chromium oxide green, and cadmium yellow) with alkyd resin, in three different pigment/binder (P/BM) ratios: 1:2, 1:3, and 1:6. The paint samples were exposed to artificial sunlight for up to 1008 h, documented by optical 3D microscopy and analysed by Infrared Spectroscopy (ATR-FTIR) and colourimetry every 168 hours. The results obtained demonstrate that the degradation processes of alkyd resin are influenced by the different inorganic pigment used and its amount/concentration in the mixtures. Evaluation of these different deterioration mechanisms took into account the morphological/colour changes, the chemical reactions, and the physical properties of the materials. This study should contribute to the field of conservation-restoration, such as finding protection strategies for surfaces from degradation agents.