IngentaConnect Fading and Colour Change of Prussian Blue: Methods of Manufacture...

Authors: Kirby, Jo; Saunders, David

Source: The National Gallery Technical Bulletin, Volume 25, Number 1, January 2004 , pp. 73-99(27)

Publisher: National Gallery

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The National Gallery Technical Bulletin, published annually, is a unique record of research carried out at the National Gallery, covering all aspects of the conservation, technical study and care of the paintings in the collection. Drawing on the combined expertise of curators, conservators and scientists, it brings together a wealth of information about artists' materials, working practices and techniques. The Technical Bulletin is an invaluable resource for art historians, collectors, and all those with an interest in Old Master paintings, as well as essential reading for conservators.

Abstract:

Prussian blue was the first totally modern synthetic pigment made as a product of a chemical reaction. The production of Prussian blue is described as difficult to control and may result in changes of colour in the final product. The chemistry of manufacture and structure of Prussian blue is discussed. Prussian blue is characterized as being inexpensive and intensely coloured and as having a high tinting strength. The presence of white pigments as an extender contributes to the permanence of the coloured paint film. Samples of Prussian blue paint films from 18th- and 19th-century paint films were studied. Samples from paintings are compared to samples prepared in the laboratory. Differences between these samples are discussed. Experimental procedures studied colour change in samples of Prussian blue- and lead white-containing paint films in cold-pressed linseed oil and watercolour media exposed to light. Reversible colour change and redox reactions are addressed. The difference in paint media did not have an effect on the degree of colour change. It is noted that the presence of alumina as an extender in paint films increased the rate of fading when paint films were exposed to light. The mixtures of Prussian blue and white pigment had an increased effect on the colour change of the paint film when compared to paint films pigmented with Prussian blue alone.

Fading and Colour Change of Prussian Blue: Methods of Manufacture and the Influence of Extenders