Study of the Behaviour of White and Black Pigments in Oil Paints: Drying, Curing, Ageing and Ion Migration

Contemporary and modern artists commonly use commercial oil paint as preferred painting materials. 20th and 21st century artists’ oils are complex mixtures that could present degradation phenomena as protrusion or crack. The research project was conducted in collaboration with the Universitat Politècnica de València (UPV). The aim of this thesis was to investigate the ageing process of commercial oil paints, monitoring the drying and curing steps and analysing the degradation phenomena that could be present in the resulting oil films. Focusing on the interaction between pigment and oil, five pigments were selected for this study: one black (Lamp Black [C]) and four whites (Lead White [2PbCO3·Pb(OH)2], Lithopone White [BaSO4·ZnS], Titanium White [TiO2] and Zinc White [ZnW]). The paints were applied as 200 nm films on a Melinex substrate, both individually and as black-and-white side by side films. Moreover, mock-ups produced in 2019 and 2021 at UPV, were used for comparison. All painting materials used for the study were provided by Golden Artist Colors, Inc. (USA). A multi-analytical approach was adopted in this research, to obtain all the information about the composition, drying and oxidative degradation of the selected oil paints. During the characterization phase, a combination of micro-invasive and non-invasive methods was applied. Fourier Transform Infrared Spectroscopy in ATR mode (FTIR-ATR) and Gas Chromatography–Mass Spectrometry (GC-MS) made it possible to analyse the binder and to detect organic compounds generated through the oil processes of auto-oxidation, film formation and hydrolysis. These together with Thermal analyses with Differential Scanning Calorimetry (TG-DSC), helped to characterize the interaction between the binder and the pigment, and the correlation with the analysis carried out in the side by side mock ups contributed to characterize the interaction between the lipic binding media and the different type of pigments. The outcome of the previous analysis where then correlated to the cases study of the painter Antonio Saura “Tajia” (1986) and “Silene” (1986), particularly suitable for this thesis project due to the artist’s predominant use of black and white paints, from the Instituto Valenciano de Arte Moderno (IVAM). Non-invasive analyses were carried in situ, while some samples were collected from the artworks to perform an invasive and destructive analysis to obtain information about the composition and the materials used by the artist.