Mechanical and Moisture Sorption Properties of Commercial Artists’ Oil Paint by Dynamic Mechanical Thermal Analysis (DMA), Nanoindentation, and Dynamic Vapour Sorption (DVS)

This study examined the physical/mechanical properties of selected artists’ oil paints. Samples included paint outs of pure paint as well as samples paints that have been modified. Dynamic mechanical analysis (DMA) and nanoindentation were used to investigate mechanical properties. DMA tests indicated appreciable differences in glass transition temperature (Tg) within each sample set. The effect of the paint modifications could be observed in terms of changes in the glass transition temperatures. Carried out at ambient temperature and controlled relative humidity conditions, the nanoindentation testing included determination of modulus values, before and after 24 h immersion in aliphatic hydrocarbon solvent, of the underside surfaces of yellow ochre and cadmium yellow paint samples. The ultramarine oil paint sample tested by nanoindentation at different relative humidities showed that the paint softened significantly by sorption of water, indicating vulnerability to permanent deformation at high moisture levels. Moisture sorption isotherms confirmed significant increases in water uptake above 60% relative humidity, especially for ultramarine. These results explain why conservators experience very different effects of temperature and moisture-based treatments.