Why van Gogh paintings are losing their shine

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(AFP) WASHINGTON — International scientists have discovered a chemical reaction that has caused the once-vivid yellows in Vincent van Gogh's paintings to turn brown, according to a study published in the United States.

A super-sensitive microscopic X-ray has revealed a chemical reaction taking place where the paint meets the varnish, triggered by sunlight which causes yellow to fade, said the findings published Monday in the journal Analytical Chemistry.

"This type of cutting edge research is crucial to advance our understanding of how paintings age and should be conserved for future generations," said Ella Hendriks of the Van Gogh Museum Amsterdam.

The X-ray from the European Synchrotron Radiation Facility in Grenoble, France also showed a reduction in chromium "was especially prominent in the presence of chemical compounds which contained barium and sulphur."
That observation led scientists to believe that "Van Gogh's technique of blending white and yellow paint might be the cause of the darkening of his yellow paint," the study said.

The best way to avoid such deterioration is to shield vulnerable artwork from ultraviolet rays and sunlight, the study authors said.

"Our X-ray beam is 100 times thinner than a human hair, and it reveals subtle chemical processes over equally minuscule areas," said Marine Cotte, a scientist with the research institute in Grenoble.

"Making this possible has opened the door to a whole new world of discovery for art historians and conservators."

The research was led by Koen Janssens of Antwerp University in Belgium. Letizia Monico, an Italian chemist, headed the experiments. Scientists from Italy, France and the Netherlands were also part of the team.

Van Gogh, known for his bold, tempestuous brushwork and having cut off his own ear, died at Auvers-sur-Oise near Paris in July 1890 after shooting himself in the chest.

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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

[...]

The darkening of the original yellow areas painted with the chrome yellow pigment (PbCrO4, PbCrO4·xPbSO4, or PbCrO4·xPbO) is a phenomenon widely observed on several paintings by Vincent van Gogh, such as the famous different versions of Sunflowers. During our previous investigations on artificially aged model samples of lead chromate, we established for the first time that darkening of chrome yellow is caused by reduction of PbCrO4 to Cr2O3·2H2O (viridian green), likely accompanied by the presence of another Cr(III) compound, such as either Cr2(SO4)3·H2O or (CH3CO2)7Cr3(OH)2 [chromium(III) acetate hydroxide]. In the second part of this work, in order to demonstrate that this reduction phenomenon effectively takes place in real paintings, we study original paint samples from two paintings of V. van Gogh. As with the model samples, in view of the thin superficial alteration layers that are present, high lateral resolution spectroscopic methods that make use of synchrotron radiation (SR), such as microscopic X-ray absorption near edge (μ-XANES) and X-ray fluorescence spectrometry (μ-XRF) were employed. Additionally, μ-Raman and mid-FTIR analyses were carried out to completely characterize the samples. On both paint microsamples, the local presence of reduced Cr was demonstrated by means of μ-XANES point measurements. The presence of Cr(III) was revealed in specific areas, in some cases correlated to the presence of Ba(sulfate) and/or to that of aluminum silicate compounds.

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@Walter Hinteler,

d'oh. Theyve determined what is the cause, now what is the cure?

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Ah, my favorite artist.

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@Walter Hinteler,

As Hitler said, "Anyone who paints the sky green and the grass blue should be castrated" .

Unless of course they are in Kentucky with an approaching hailstorm.

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@Ionus,

Ionus wrote:

As Hitler said, "Anyone who paints the sky green and the grass blue should be castrated" .

Since you seem quite acquainted with this person - what has/had to do with these findings?

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The best way to avoid such deterioration is to shield vulnerable artwork from ultraviolet rays and sunlight, the study authors said.

These people have been keeping priceless works of humanity's cultural heritage in the sunlight?!

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@InfraBlue,

lots of museums had vertical shaft lighting which was mostly sunlight. I think the photochemistry was only realized in the sixties when the da Vinci at the US National Gallery began getting some really funky colors. I dont know what they did but they did move it into a totally artificial light environment.

One of the very first lessons conservators learned was for Federalist painted furniture and some earlier icons. The color blue was a copper carbonate and it was infused into what we now call milk paint and some other oil based pigments. Over time the bright blues turned to green. This didnt occur in Vermeers paintings cause he ground up a silicate mineral for his ultramarine blues. His blues look as crisp as when they were painted. Michelangeloas Chapel ceiling looked like a bag of **** for many centries from grime, light, chemical fading, and shitty restorations. SO once they got it stabilized, then they got it cleaned up and now the blues are in good condition.

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@farmerman,

Sure, but it didn't take a photochemical analysis for me to realize early on in life that leaving certain things exposed to sunlight will screw with their colors--like the posters on a Dairy Queen window, or the back of the living room couch.

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@Walter Hinteler,

Just a piece of useless trivia, Walt. That and the insinuation that anyone who doesn't find Van Gogh interesting might be comparable to Hitler.

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Why van Gogh paintings are losing their shine

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