Investigating the Effect of Linseed Oil on Paper Supports via VOC Emissions: Markers for Condition Assessment: Heritage

Oil paintings, sketches, and printed works on paper frequently exhibit characteristic forms of deterioration caused by the absorption of linseed oil binders into the paper substrate. This study investigates for the first time the factors influencing the resulting volatile organic compound (VOC) emissions from oil-impregnated papers upon ageing and explores VOC quantifiable metrics suitable for condition assessment. Headspace Solid-Phase Microextraction coupled with Gas Chromatography-Mass Spectrometry (HS-SPME–GC-MS) was employed to sample and analyse VOCs from mock-ups made of three types of paper (a pure cellulosic, lignin-free and lignin-containing lignocellulosic papers with alkaline buffer), three pure linseed oil formulations (cold-pressed and alkaline-refined linseed oil, and stand oil), and oil-impregnated paper mock-ups, all subjected to controlled artificial ageing. The results showed a clear difference in VOC profile emissions between pure papers and linseed oil formulations, while oil-impregnated mock-ups emitted compounds matching those of the linseed oil formulations; however, the emissions followed a different trend. Statistical analysis (PCA) demonstrated that both paper pulp content and oil formulation significantly influence VOC emission patterns, highlighting the compounds that produce higher and most characteristic emissions. Ratios of specific compounds—such as formic to acetic acid—showed consistent trends across materials, indicating their potential as markers for distinguishing stages of deterioration.