It is well known that the rise of Impressionism was due in part
to the new developments in paint chemistry which created brighter, more stable
colors previously unavailable for oil painting.
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| View of Arles with Irises by Vincent van Gogh, oil painting. |
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One of the artists who embraced and experimented with the new
color technology was Vincent van Gogh. The brilliance of some of van Gogh's
most famous fine art oil paintings are due to his use of these newly available vivid
industrial pigments. These pigments begin to show up in his work after his move
from Holland to France. Unfortunately, the chemists of the time did not have
the tools to perform accelerated aging tests to determine the lightfastness
over time of their new creations.
One of the colors, Chrome Yellow, is not only
toxic, but is now also known to darken under exposure to the ultraviolet rays
in sunlight. As less toxic alternatives to Chrome Yellow were finally developed
in the mid-1900s, artists tended to switch to them. But, for a critical period
of time, the brilliant color that Chrome Yellow provided was an important tool
in van Gogh's and other artists' palettes. It was perhaps most famously used in
some of van Gogh's Sunflower paintings. Researchers have found that some, but
not all, paintings containing chrome yellow suffer from the severe browning
that exposure to sunlight can cause.
To understand how paintings age and how best to preserve them
for the future, researchers conducted an in-depth study of the browning seen in
some of Van Gogh's work painted with Chrome Yellow. Scientists from four
countries performed the study. They began by collecting samples from three
historic chrome yellow paint tubes and artificially aging the paint for 500
hours using an ultraviolet lamp. They also took samples from two van Gogh
paintings,
View of Arles with Irises and
Bank of the Seine. The paint from the
tubes darkened to a chocolate brown after exposure to the UV light.
Using an
X-ray beam that is one hundred times thinner than a human hair, the scientists
were able to analyze the darkened chrome yellow at the very surface of the two
paintings as well, just below the varnish. Their analyses discovered that the
chromium in the pigment gained electrons from the UV light, effectively
reducing Chromium (VI) to Chromium (III), turning bright yellow to brown.
Of great interest was the finding from the microscopic X-ray
beam that the darkening was most prominent where chemical compounds containing
barium and sulphur were. This may prove why some of Van Gogh's paintings seem
to be especially susceptible to the darkening, as it is speculated that he
sometimes blended white (containing barium and sulphur) with his yellow paint.
The next phase of the research will be the most important of all in trying to
understand if there is any hope to revert pigments to the original state in
paintings where the darkening is already taking place.
In yet another blending of science and art, we are able to look
backwards to understand more about the lives and the works of the great
masters. "I am not aware of a similarly big effort ever having been made
for the chemistry of an oil painting." - Joris Dik, Professor at Delft
Technical University. (More information is available from the Journal of
Analytical Chemistry.)
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The Artist's Road for more interesting and informative stories.
We believe that more artists in the world is a good thing!
--John and Ann
