A New Perspective on the Phenomenon of ’Ultramarine Disease’ in Paintings
Failure of ultramarine blue paint layers in historic as well as modern paintings has been reported in the literature many times and is often referred to as “ultramarine disease” or “ultramarine sickness.” The pigment itself is known to degrade hydrolytically when exposed to acids, but whether this is the primary cause of the failure remains unclear. A study at CRCC in collaboration with the University of Amsterdam, Pratt Institute in New York and the Technical University of Delft focused on ultramarine blue paints using linseed oil and a urea-aldehyde resin as binding media. The paints, prepared by Gambin Artist Colors, were aged under simulated indoor conditions.
The paints were analyzed using reflectance spectroscopy, scanning electron microscopy, and Raman and nuclear magnetic resonance spectroscopy. The urea-aldehyde resin binding medium was analyzed using size exclusion chromatography and Fourier-transform infrared spectroscopy. The study provides evidence of photo-catalytic degradation of binding media of ultramarine blue paint layers via free-radical processes, causing changes in reflectance while the pigment itself remains intact. It is believed that this is the primary process behind the degradation of ultramarine blue paint layers in paintings.
Ultramarine blue has a zeolite structure and the results are in agreement with the photo-catalytic activity of other zeolites. The sulfur radical anion color centers trapped in the zeolite cage do not appear to play a role in the process and the cage itself remains intact. The free radical process can be inhibited with a hindered amine light stabilizer.
DR-UV-vis reflectance spectra of ultramarine blue in linseed oil before aging and after aging for ca. 1500 hrs in a xenon arc chamber.
FEG-SEM images and photographs of ultramarine blue in linseed oil, before aging (left) and after aging for ca. 1500 h in a xenon arc chamber (right).
René de la Rie, Anne Michelin, Manuela Ngako, Eleonora Del Federico, Chelsey Del Grosso,
Photo-catalytic degradation of binding media of ultramarine blue containing paint layers: A new perspective on the phenomenon of “ultramarine disease” in paintings,
Polymer Degradation and Stability, Volume 144, 2017, Pages 43-52, ISSN 0141-3910,