20th century oil paint formulations: an analytical challenge in the conservation of modern and contemporary heritage.

From the 19th Century, artists’ oil paints were increasingly produced on an industrial scale and include a number of additives, e.g. stabilisers, dispersion agents and driers [1]. These additives allowed for faster production, stability, prolonged shelf life and uniform handling properties of the paints in and from the tubes. In particular, aluminium and zinc stearates were introduced as wetting and dispersion agents for the pigments and as stabiliser for the paint. However, the incorporation of stearates into manufactured oil paints may cause water sensitivity during surface cleaning of unvarnished paintings [2,3]. The aim of this research was to investigate 20th century manufactured oil paints by developing an analytical methodology for the detection of metal soaps and lipidic additives using Gas Chromatography Mass Spectrometry (GC-MS). A methodology for the detection of metal stearate and fatty acid additives was designed by analysis of selected oil paint films. In addition, commercial tube oil paints from Winsor&Newton, Old Holland, Talens, Gimborn, and Maimeri were tested.The developed analytical procedure was also used for the analysis of samples from 20th century oil paintings by Lucio Fontana, Jasper Johns, Karel Appel, Willem de Kooning, and others. The results obtained pointed out the employ of different kinds of oil media (such as linseed oil, rapeseed oil, castor oil, safflower oil, sunflower oil, etc) and the presence of additives (such as stearates, hydrogenated castor oil, waxes, etc). The identification of binding media and additives in paint samples is important for the knowledge about painting techniques and to understand degradation phenomena which occurr in modern and comtemporary works of art as well. This knowledge may also play a role in the design of conservative practice. [1] Gauld Bearn J., The chemistry of paints, pigments and varnishes, London, Ernest Benn 1923 [2] Burnstock A., van der Berg K. J., de Groot S. et alii, An investigation of water-sensitive oil paints in the 20th century paintings, in Learner T. J. S., Smithen P., Krueger J. et alii, Modern Paints Uncovered, Los Angeles, The Getty Conservation Institute 2007, pp. 177-188 [3] Wijnberg L., van den Berg K. J., Burnstock A. et alii, Jasper Johns’ Untitled 1964-65, in Art matters, (2007), pp. 68-8