February 14, 2011
Chemical Reaction Found In Van Gogh’s Paintings
Scientists have identified why the bright yellows in Vincent van Gogh's paintings have turned brown.
They say that a complex chemical reaction is behind the deterioration of the works.The new finding is a first step in understanding how to stop some of van Gogh's most famous paintings from fading over time.
The results suggest shielding the affected paintings as much as possible from UV and sunlight.
Scientists had to use an array of analytical tools in order to uncover the secrets of the chemical reaction.
Sunlight can penetrate only a few inches into the paint, but the researchers found that it could trigger a hitherto unknown chemical reaction turning chrome yellow into brown pigments, altering the original composition.
The scientists employed a microscopic X-ray beam to reveal a complex chemical reaction taking place in the thin layer where the paint meets the varnish.
The vibrancy of new industrial pigments like chrome yellow allowed van Gogh to achieve the intensity of his series of Sunflowers paintings.
He started to paint in these bright colors after leaving his native Holland for France where he became friends with artists who shared his new ideas about the use of colors.
The team found a change in the oxidation state of the element chromium was linked to the darkening of chrome yellow paint.
The X-ray beam research carried out at ESRF showed that chromium 3 was especially prominent in the presence of chemical compounds, which contained barium and sulphur.
The scientists speculate that based on this observation, van Gogh's technique of blending white and yellow paint might be the cause of the darkening of his yellow paint.
Co-author Koen Janssens told BBC: "Our next experiments are already in the pipeline.
"Obviously, we want to understand which conditions favor the reduction of chromium, and whether there is any hope to revert pigments to the original state in paintings where it is already taking place."
The research was published in the journal Analytical Chemistry.
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