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Direct speciation analysis by X-rays show why van Gogh paintings lose their shine

(21.02.2011)


Background:
Van Gogh’s decision to use novel bright colours in his paintings is a major milestone in the history of art. He deliberately chose colours that conveyed mood and emotion, rather than employing them realistically. At the time, this was completely unheard of and, without major innovations in pigment manufacturing made in the 19th century, would also have been impossible.

It was the vibrancy of new industrial pigments such as chrome yellow which allowed van Gogh to achieve the intensity of, for example, his series of sunflower paintings. He started to paint in these bright colours after leaving his native Holland for France where he became friends with artists who shared his new ideas about the use of colours. For one of them, Paul Gauguin, he started painting yellow sunflower motifs as a decoration for his bedroom.

The fact that yellow chrome paint darkens under sunlight has been known since the early 19th Century. However, not all period paintings are affected, nor does it always happen at the same speed. As chrome yellow is toxic, artists switched to new alternatives in the 1950s. However, Vincent van Gogh did not have this choice, and to preserve his work and that of many contemporaries, interest in the darkening of chrome yellow is now rising again.


The new study:

The work was carried out by an international team of scientists from Belgium, Italy, France  and the Netherlands. An impressive arsenal of analytical tools was used to reveal how the bright yellow colours of van Gogh's most famous paintings, as well as other artists of the 19th century, became lacklustre and faded over time, with synchrotron X-rays at the ESRF in Grenoble (France) providing the final answers. 

For every Italian, conservation of masterpieces has always mattered. I am pleased that science has now added a piece to a puzzle that is a big headache for so many museums” says Letizia Monico from University of Perugia.



This illustration shows how X-rays were used to study why van Gogh paintings lose their shine. Top: a photo of the painting "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.
Bottom left: microscopic samples from art masterpieces moulded in plexiglass blocks. The tube with yellow chrome paint is from the personal collection of M. Cotte.
Bottom right: X-ray microscope set-up at the ESRF with a sample block ready for a scan. Centre: an image made using a high-resolution, analytical electron microscope to show affected pigment grains from the van Gogh painting, and how the colour at their surface has changed due to reduction of chromium. The scale bar indicates the size of these pigments. Credit: ESRF/Antwerp University/Van Gogh Museum.


The scientists employed 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. Sunlight can penetrate only a few micrometres into the paint, but over this short distance, it will trigger the reduction of the hexavalent chromium to the trivalent state, turning chrome yellow into brown pigments. 

The microscopic X-ray beam also showed that Cr(III) was especially prominent in the presence of chemical compounds which contained barium and sulphur. Based on this observation, the scientists speculate that van Gogh’s technique of blending white and yellow paint might be the cause of the darkening of his yellow paint.

Our next experiments are already in the pipeline. Obviously, we want to understand which conditions favour 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.”, summarises Koen Janssens from University of Antwerp.

Source: adapted from ESRF


The original study

Letizia Monico, Geert Van der Snickt, Koen Janssens, Wout De Nolf, Costanza Miliani, Johan Verbeeck, He Tian, Haiyan Tan, Joris Dik, Marie Radepont, and Marine Cotte, Degradation Process of Lead Chromate in Paintings by Vincent van Gogh Studied by Means of Synchrotron X-ray Spectromicroscopy and Related Methods. 1. Artificially Aged Model Samples, Anal. Chem., 83/4 (2011) 1214–1223. DOI: 10.1021/ac102424h

Letizia Monico, Geert Van der Snickt, Koen Janssens, Wout De Nolf, Costanza Miliani, Joris Dik, Marie Radepont, Ella Hendriks, Muriel Geldof, and Marine Cotte, 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, Anal. Chem., 83/4 (2011) 1224–1231. DOI: 10.1021/ac1025122


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last time modified: February 21, 2011



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