Investigating the effect of oil binders on the paper supports via statistical analysis. Part 1: the factors that influence the resulting changes upon ageing

Condition assessment of works of art created with oil paints and traditional oil-based inks on paper can be quite complex, especially when it comes to understanding alterations and damages resulting from the absorption of oil binders into the paper support. Recently, a comprehensive methodology was implemented to study the effect of three linseed oil formulations on colour, opacity, morphology, tensile strength, and chemical properties on a pure cellulosic and two lignocellulosic papers with alkaline buffer, using oil-impregnated mock-ups subjected to accelerated, humid-thermal ageing in air-tight vessels. The results generated a substantial amount of data, including measurements of colour, opacity, tensile strength, pH, as well as analyses using Fourier Transform Infrared Spectroscopy (FTIR), and Volatile Organic Compound (VOC) analysis with Gas Chromatography-Mass Spectrometry (GC-MS). However, a comparative study of the results was insufficient to draw definitive conclusions about the influence of main factors of research—such as ageing time, paper type, and linseed oil formulation—on the recorded changes. Statistical analysis of variance (ANOVA) and Principal Component Analysis (PCA) were employed to reveal the influence of the factors (time of ageing, paper type and linseed oil formylations) on the parameters of research, and to identify the possible correlation between the sets of the impregnated mock-ups. ANOVA testing, involving results from colourimetry, opacity and pH measurements, as well as those derived from GC-MS analysis of VOC emissions, indicated that the three factors have different inputs to many parameters of the research. PCA revealed that there is a distinct difference in the resulting changes between the mock-ups made of the pure cellulosic paper and the two lignocellulosic papers with alkaline buffer upon ageing. Both tests also showed similarities between the mock-ups impregnated with cold-pressed and refined linseed oil. Finally, time-based clustering of the various sets of mock-ups could be suggested, providing a foundation for condition assessment and rating.