An investigation into the separation and migration of oil in paintings by Erik Oldenhof

The observation of disfiguring yellow oil-like material on the surface of paintings by the contemporary Dutch artist Erik Oldenhof led to an investigation of the material and environmental factors causing the migration and surface deposition of the exudate. A combination of material analysis, the examination of artificially aged reconstructions and information provided by the artist and paint manufacturer, Royal Talens, provided evidence that the phenomenon is related to the drying properties of the safflower oil used, the artist's use of thick paint layers and the availability of light while the paint is drying. Reconstructions demonstrated that the exudation phenomenon can be reproduced and is not restricted to one particular range of oil paint or manufacturer. Visual characteristics of the exudate, including its appearance in UV light and SEM back-scattered images, were documented, and the organic and inorganic components of the paint were characterised by SEM-EDX, XRF, THM-PyGC-MS and FTIR. Results confirmed that the exudate is composed of safflower oil derived from the paint binding medium, and that a difference in P/S ratio between the exudate and paint bulk is due to the presence of metal stearates in the paint that have not migrated to the surface.