Faded Sunflowers: Why Van Gogh's Yellows Are Turning Brown

By Andrew Moseman | February 15, 2011 12:04 pm

Walking the halls of one of the world’s great art museums, it’s easy to regard familiar classic paintings as eternal and unchanging. But this is not the case. Paintings are a mix not only of color but of chemistry—and chemistry changes. In some of Vincent van Gogh’s works, the striking, sunny yellows have faded and turned brownish, robbing the Dutch master’s art of some of its trademark intensity. So a European team of scientists decided to find out exactly what was happening on those canvases.

Using sophisticated X-ray machines, they discovered the chemical reaction to blame — one never before observed in paint. Ironically, van Gogh’s decision to use a lighter shade of yellow paint mixed with white is responsible for the unintended darkening, according to a study published online Monday in the journal Analytical Chemistry. [Los Angeles Times]

Vincent loved yellow. In particular, he loved chrome yellow, a 19th century invention that shone brighter than previously available hues of paint. Art preservationists have known that the lead-based paint fades under intense sunlight, so they’ve done what they can to keep van Goghs and similar works out of intense light. What’s curious about his paintings, however, is that some yellows have faded while others have not.

To sort this out, the team led by Koen Janssens first acquired paints made around the time van Gogh worked, and then blasted them with UV light to simulate the aging process. When one of Janssens’s yellow samples browned the way some van Goghs have, the team examined it with X-ray scans at the European Synchrotron Radiation Facility in Grenoble, France.

The researchers found that a change in the oxidation state of the element chromium (from chromium 6 to chromium 3) was linked to the darkening of chrome yellow paint. The X-ray beam research carried out at ESRF also showed that chromium 3 was especially prominent in the presence of chemical compounds which contained barium and sulphur. [BBC News]

For comparison, Janssens then looked at tiny paint flecks from two van Goghs: Banks of the Seine (above) and View of Arles with Irises. And in the yellows that had browned, the team found their culprit in forcing the chromium change: barium sulfate.

This suggests that this contaminant, combined with light exposure, is the source of the darkening, Janssens [says]: “We think the barium sulphate could have been part of a paint extender – something used to make the paint go further. The mixture of sulphate and chromate is very sensitive to darkening under UV light. Galleries should keep paintings containing chrome yellow out of any strong light or UV light.” [New Scientist]

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Image: Van Gogh Museum

CATEGORIZED UNDER: Physics & Math, Technology, Top Posts
  • Idlewilde

    The lesson here? Don’t use paint extender :)

  • http://clubneko.net/ nick

    Quick, someone get out the time machine and go warn Van Gogh!

    (this comment quickly explains why the artist went insane)

  • StankyLeg

    Wow, what nick said made a lot of sense.

  • http://charleszigmund.com Charles

    The Old Masters, from the 15th century through the middle of the 19th, ground and mixed their own oil paints and understood the properties of the pigments and mediums they employed, or that they directed their studio assistants in employing. They knew how to keep their paintings from darkening or fading over hundreds of years. On the other hand, the Impressionists were the first generation of artists that bought manufactured oil paints rather than make their own. In particular, whites and yellows in oil paint must be formulated and worked with very carefully to keep from darkening, and the old masters understood the rules for this, while the moderns just laid on the paint. Older paintings were also covered with removable varnish to protect the painting. The varnish can be removed easily with turpentine when it gets dirty from the air, leaving the original painting below unchanged. A new coat of removable varnish can then be applied which will last for another 50 or 100 years before needing to be removed and replaced again, and so on.

    I will never forget the stunning experience of seeing Titian’s “Sacred and Profane Love”, painted in 1514, at the Borghese Gallery in Rome several years ago. It looked as fresh, and the color as vivid, as if it had been painted the same day. It even looked wet, yet it was almost 500 years old. No doubt the protective varnish has been removed and replaced many times. Some Impressionist and modern paintings look far older.

    Artists today like myself who may use acrylic paint don’t have to worry about this, as acrylic does not have the same changing and darkening properties as oil. It is however not as rich in texture and feel as oil. Artists who use oil today do so at the risk of their paintings changing over time, like Van Gogh’s, unless they learn and follow the necessary techniques, especially with whites and yellows.

  • John Lerch

    OTOH we’ve had many critics oohing and aahhing over Tibetan sand paintings; the oohs and aahs are in fact much because they’re here today and gone today.

  • http://charleszigmund.com Charles

    Back on the OTHER other hand, I’m really glad Titian, Rembrandt, Cezanne and a lot of others I could name were not sand painters but oil painters.

  • http://www.nicky510.com Crow

    Find the right media is always a challenge: http://www.nicky510.com/comic/its-a-polar-bear-in-a-snowstorm/


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