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Analyses of Marianne North paintings

Chemical analyses of Kew’s Marianne North oil paintings have helped in their conservation.

The deep blue pigment in this Marianne North painting (number 110 ‘Night Flowering Lily and Ferns, Jamaica’) was identified as indigo.

Conservation work was performed on Kew’s Marianne North oil paintings (on paper) between 2008 and 2011, in a purpose built on-site conservation studio located in the Herbarium. The conservation activities included research to identify the pigments that had been used, the oil used to bind the pigments, and the varnish used to cover the finished painting. As many components of paint are derived from plant material, some of the research could be performed using Kew’s analytical facilities.

LC-MS analysis of a paint sample shows that it matches indigoitin (indigo).

Analyses of paints, oils and varnishes

Very small paint samples were taken either from the edges of the painting or from paint that had become detached. The samples were analysed by liquid chromatography-mass spectrometry (LC-MS) and compared with reference samples of dye based pigments that were likely to have been used, such as madder (Rubia) and indigo (Indigofera), obtained from the Kew’s Economic Botany Collection. Oils and varnishes were analysed both by LC-MS and gas chromatography-mass spectrometry.

Several successful identifications were obtained. Poppy seed oil was found as a component of the oil media, mastic resin with Venice turpentine was detected in the varnish, and indigo (indigotin) was found in samples of a deep blue pigment from one painting (number 110).

Informing conservation decisions

The analyses were used to inform conservation treatment decisions as knowledge of the materials used is important in selecting appropriate treatments and techniques that do not pose a risk to sensitive compounds, such as dye based colours. The work has also helped us to better understand and appreciate the collection and Marianne North’s working methods.

The positive results of this work will encourage future use of our on-site facilities in the analysis of Kew’s art materials.

Item from Emma Le Cornu (Conservator, RBG Kew)
Kew Scientist, issue 40

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