Analytical chemistry on micro-imaging of industrial and historical paints
The invention of oil paintings fundamentally relied on driers, required to speed up the oxidation of oil double bonds and its polymerization. Historically, these driers were metallic oxides (e.g. PbO), forming soaps by reaction with oil. Sometimes, such metal soaps have concentrated in specific parts of the paint layer, affecting the integrity of the work (e.g. protrusions, delamination, etc.). Today, oil has been replaced by alkyds and lead by the less, but still toxic cobalt. Efforts are paid to develop safer (for human and for environment) driers, mainly based on Mn and Fe. Reactions involved during paint drying are generally followed at the macro-scale. The spatial distribution of these reactions over the paint thickness are usually neglected by the paint companies. This is however important since sedimentation, contact to the support, distance to the surface (O2, light and later pollutants) can affect the drying and ageing reactions.
We propose to extend the use of micro-imaging techniques (μXRF, μXAS, μXRD and μFTIR), regularly employed on fragments of historical paintings, to the study of drying reactions. Sample corpus contain historical samples where the (mis-) use of driers is suspected and paint films prepared following both the formulations developed at AkzoNobel and historical recipes. The student develops an “all-inclusive” procedure: from the analysis of historical texts, the preparation of model samples, their analysis at the bulk and the microscale to the comprehensive data analysis. In addition to this protocol which could be later exploited for other studies, this work provides a unique comparison between ancient and modern driers, and should path the way for innovative paintings.
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