Scientists have identified a complex chemical reaction responsible for the degradation of two paintings by Vincent van Gogh and other artists of the late 19th century. This discovery is a first step towards understanding how to stop the bright yellow colours of van Gogh’s most famous paintings from becoming covered by a brown shade, and fading over time.
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: May 17, 2024
