UV Rays Found to Damage Priceless Painting

Ever wonder why art museums prohibit photography of already-well-known paintings? Scientists in France have discovered a tricky conundrum behind the fading of colors in paintings by Vincent Van Gogh. After a series of invasive observations, researchers at the European Synchrotron Radiation Facility (ESRF) in Grenoble have discovered that exposure to UV rays will gradually alter the yellow and brown pigments in paint.

"Bank of the River Seine" on display at the van Gogh Museum, divided in three and artificially coloured to simulate a possible state in 1887 and 2050. photo courtesy of ESRF

ESRF scientists Koen Janssens of Antwerp University in Belgium and chemist Letizia Monico of Perugia University in Italy led a team using "an X-ray beam of microscopic dimensions to reveal a complex chemical reaction taking place in the incredibly thin layer where the paint meets the varnish." The chrome yellow tints, like those used in van Gogh's "Sunflowers," darken over time due to a chromium compound change from Cr(IV) to Cr(III), the latter containing amounts of barium and sulfur. 

"View of the Arles with Irises," 1888. Vincent van Gogh

Two paintings were examined by the team: View of Arles with Irises (1888) and Bank of the Seine (1887). van Gogh began using this combination of colors when he entered the French artistic community in the late 1800s as a part of the Post-Impressionistic movement. According to the BBC, "scientists speculate that van Gogh's technique of blending white and yellow paint might be the cause of the darkening of his yellow paint."

Paint samples were taken from historic tubes. ESRF artificially aged the samples under a UV lamp, but only paint from one tube showed noticeable brownish tones after 3 weeks.

Experts speculate that the reason not many works from the period experience the same chemical reaction is because chrome yellow paint is toxic, and therefore artists began switching their materials in the early twentieth century.

Sources:

"Van Gogh Paintings 'Degraded by UV-Driven Reaction.'" BBC News

http://www.bbc.co.uk/news/science-environment-12453610

"X-Rays Show Why Van Gogh Paintings Lose Their Shine." European Synchrotron Radiation Facility

http://www.esrf.eu/news/general/van-gogh/van-gogh-paintings-lose-shine/

"Degradation Process of Lead Chromate in Paintings by Vincent van Gogh Studied by Means of Synchrotron X-ray Spectromicroscopy and Related Methods. 2. Original Paint Layer Samples." Analytical Chemistry

http://www.esrf.eu/news/general/van-gogh/van-gogh-paintings-lose-shine/