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Metal soap formation is a recently identified phenomenon observed in oil paintings spanning the thirteenth to the twentieth centuries. The soaps are caused by a reaction between the oil medium and metal ions present in the paint. These metal ions are most commonly lead- and, more recently, zinc-containing pigments or additives. Research in Europe and the United Kingdom has linked soap formation to dramatic deterioration in some paintings.
The study of paint cross-sections from some nineteenth- and early twentieth-century British and Australian paintings in the Gallery's Collection indicate that a significant number appear to contain zinc soaps. The paintings of interest do not generally exhibit obvious surface deterioration. It is possible the incidence of soaps reflects an earlier state of the deterioration currently under investigation in Europe.
Paintings in the Gallery's Collection by R. Godfrey Rivers ― including Under the jacaranda 1903 (illustration 1) ― have been examined as part of this study. Highly ultraviolet-fluorescent material is distributed through certain layers of the artist's paintings dating from 1890 to 1904. Zinc is consistently found at the centre of fluorescent regions, and zinc has been found in samples from selected art works. In illustration 2, an ultraviolet fluorescent image of a paint cross-section of the jacaranda flowers shows layers of paint containing cobalt blue, lead, zinc and organic crimson lake.
Research into the incidence of zinc soap formation in the Gallery's Collection is ongoing. It will attempt to increase the understanding of the circumstances in which the soaps form. The stability and long-term implications of the presence of the soaps is also under investigation.
Gillian Osmond is Conservator (Paintings) at the Queensland Art Gallery.
Read more about R. Godfrey Rivers's Under the jacaranda 1903 in Collection highlights.
