Light-induced Colour Changes in Red and Yellow Lake Pigments

David Saunders and Jo Kirby
Technical Bulletin Volume 15, 1994

Abstract

Notes 18th-century views on the impermanence of cochineal and brazilwood red lakes. Describes faded cochineal identified in paintings by Reynolds and Gainsborough, and faded lac lake in a Jacopo di Cione. Loss of organic reds is noticeable through loss of modelling in red and purple paints, while loss of organic yellows is apparent in 'blue' foliage or fruit, particularly in Dutch 17th-century paintings and those of Greuze. Previous studies of the lightfastness of organic pigments are noted: most included modern industrial products, not traditional pigments, even when carried out in the later 19th century.

In a very comprehensive study, pigment samples were prepared by the authors by dyeing wool with cochineal, kermes, lac, or madder and then extracting the dye with alkali and precipitating it onto alum. Brazilwood, modern alizarin crimson and yellows extracted from buckthorn, quercitron and weld were also used. Samples of each in gum arabic, egg tempera, or linseed oil, some mixed with lead white 1:1 to 1:3, were painted out, aged under fluorescent lamps, and colour measurements were made. (Details are given).

Anthraquinones such as alizarin and madder are the most stable for a given substrate, and tin-based substrates were the least stable. Weld was the least fugitive yellow. Yellow dyes and carmine on an aluminium-containing substrate were more stable than on other substrates. Thick or heavily-pigmented layers faded less than thin ones. Lead-white samples showed altered tonal gradation after light aging.

Keywords 

brazilwood, cochineal, dye, kermes, lake (pigment), lightfastness, madder, organic pigment, tempera

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To cite this article we suggest using

Saunders, D., Kirby, J. 'Light-induced Colour Changes in Red and Yellow Lake Pigments'. National Gallery Technical Bulletin Vol 15, pp 79–97.
http://www.nationalgallery.org.uk/technical-bulletin/saunders_kirby1994

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