Ion migration mechanisms in the early stages of drying and degradation of oil paint films

Abstract

The study of film-formation processes of oil paints has been extensively addressed over the last decade and the influence of metal ions in the drying and degradation stages of oil paints has been demonstrated. This research aimed to determine a suitable methodology for monitoring the early drying stages of selected commercial oil paint films and to gain an insight into the migration mechanisms of material degradation taking place between adjacent paint films, with special attention to the influence of the lead white. For this purpose, a hybrid approach was adopted to characterize the composition of the paint and highlight failure mechanisms in the paint films through a wide range of time. The methods included scribe tests, percentage weight variation (ΔW%), attenuated reflectance Fourier transform infrared spectrophotometry (ATR-FTIR), gas chromatography-mass spectrometry (GC-MS), and thermal analysis with differential scanning calorimetry (TG-DSC). The results show how metal ions interact with the oil binder and the pigment in the adjacent paint film: the transverse migration of lead white is shown to affect the reactivity of polyunsaturated triglycerides, increasing the rate of oxygen uptake and promoting the formation of radicals and bonds between polymer chains, depending on the pigment with which it interacts.