Vincent van Gogh, 1889
The binding medium of the yellow lead and zinc chromate paint in the Sunflowers seems to have degraded to such an extent that it poses a serious challenge to the pending conservation and restoration treatment (2012-13). Although the surface has formed a solid crust, the paint below is very crumbly and powdery. Collapse of impasto with paint loss is a result. Surface examination and an available paint cross-section shows the formation of lead soap aggregates. The paint is extremely sensitive to organic solvents such as acetone.
Previous research has focused on the discoloration of the yellow lead and zinc chromate pigments themselves, but the question of the effect of the pigment on the binding medium and internal cohesion of the paint remains [Monico et al. 2011].
The aspect of discolouration in The Sunflowers will be a theme within the proposed Science4Arts project Re-assessing Vincent van Gogh’s use of colour using digital reconstructions (Prof. dr. E.O. Postma (UvT): lessons for the conservation of paintings and drawings. The research proposed here forms an essential complement to the understanding of why the deteriorated areas of chrome yellow look the way they do.