Identifying the plant origin of artists' yellow lake pigments by electrospray mass spectrometry

Dyes containing flavonoids are found in yellow lake pigments used as artists' materials. Pre-treating a sample of a flavonoid-based lake pigment with an acidic ion exchange resin followed by reversed-phase HPLC electrospray mass spectrometry enables the identification of key diagnostic yellow compounds, even when the pigment is bound in paint media. Reference raw plant materials of weld and buckthorn berries were also treated similarly for comparison with the lake pigments derived from these plants. This method is suitable for microsamples and thus suitable for analysis of samples that can be ethically removed from works of art in the course of their conservation. The flavonoid content is analysed and plant origins are suggested for yellow lake samples taken from Reclining Tiger by Jean-Baptiste Oudry and the 1893 version of The Scream by Edvard Munch