In order to be exposed to the public in pristine condition, paintings in collections all over the world are repeatedly exposed to organic solvents for the removal of varnishes and to aqueous solutions for surface cleaning. The focus of this project is the study of degradation phenomena related to the cleaning of paintings.
Within museums, specific climate control regulations are generally accepted as a good strategy for limiting degradation phenomena in paints. However, these measures and regulations are often based on practical experience and risk limitation. On a molecular level, the influence of environmental conditions on reactions inside aging oil paints are not yet well-understood.
We set out developing a method and model to measure and describe the solvent diffusion and swelling in paint models. Using time-dependent ATR-FTIR, the formation of metal soaps was studied in oil paint model systems, allowing us to identify crucial factors in the crystallization process. In bilayer systems, it was then possible to show that solvent exposure can enhance the migration rate of fatty acids between layers and the formation of metal soaps. Several methods of solvent exposure were compared and important differences between methods identified.
The most recent development is the use of Laser Speckle Imaging (LSI) for quantitative comparison of solvent application methods and solvent properties on heterogeneous and cracked paint surfaces. This portable method can therefore be used on real paintings during varnish removal.
Carried out within the framework of the NANORESTART project
(EUHorizon 2020 agreement No 646063)
Joen. J. Hermans, Lambert Baij, Mark Koenis, Katrien Keune, Piet D. Iedema and Sander Woutersen. (2019). 2D-IR spectroscopy for oil paint conservation: Elucidating the water-sensitive structure of zinc carboxylate clusters in ionomers.