Delamination of oil paints from acrylic grounds
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Many modern artists paint in oil or oil-modified alkyd paints over acrylic grounds. In some cases the oil based paints do not remain adhered to the ground. In a set of composite samples of oil or alkyd paints, over acrylic grounds, naturally aged for nine years, some of the samples delaminated. Samples were analyzed with X-ray fluorescence (XRF), inductively coupled plasma (ICP), Fourier transform infrared - attenuated total reflectance (FTIR-ATR), scanning electron microscopy (SEM), pyrolysis gas-chromatography mass-spectrometry (PY-GC/MS), laser desorption/ionization mass-spectrometry (LDI-MS), atomic force microscopy (AFM) and other methods, in order to find what the delaminating ones have in common. In addition, two examples of severely delaminating paintings were examined, to confirm the results from the laboratory-prepared samples. Results indicate the main cause of delamination is metal soaps in the oil paint and particularly zinc soaps. There is some evidence that metal soaps were more concentrated at the interface between the layers and this disrupted the adhesion. The ground is a minor consideration as well, rougher grounds providing better adhesion than smooth ones.