Issue Date: March 12, 2018
Method identifies subtypes of yellow pigment in Van Gogh’s ‘Sunflowers’
With X-ray powder diffraction, Frederik Vanmeert of the University of Antwerp and coworkers have analyzed the number and distribution of chrome yellow pigments, known for their tendency to discolor, in three regions of “Sunflowers,” painted by Vincent van Gogh in 1889 (Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201713293). Chrome yellows are a class of inorganic pigments. Lightfast chrome yellow, which is fade-resistant, contains PbCrO4. In light-sensitive chrome yellow, which is prone to darkening under the influence of light, some of the CrO42– is replaced by SO42–. Different light-sensitive subtypes have different amounts of sulfate. The researchers found chrome yellow in darker yellow flowers, lighter ones, and in the background, as well as mixed with other pigments. In addition to lightfast chrome yellow, they found one light-sensitive subtype. Each subtype was present on about one-third of the examined painting surface. The researchers found lightfast chrome yellow mainly in orange-yellow regions, whereas light-sensitive chrome yellow was in the bright yellow regions. They also visualized overlapping layers of the two subtypes and more complicated mixtures of the yellows with other pigments. The findings will allow conservators to identify regions of the painting at higher risk of degradation and will also aid art historians with digital reconstructions of the original colors used by Van Gogh, the researchers note.
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