Much has been made of the advances over the centuries, and particularly in the last century or two, in paint chemistry, allowing artists to work with an ever-broadening array of pigments, and often providing much needed replacements for older, plant-based pigments that were fugitive over time.
Not all advances in paint technology are for the better in that respect, however. A case in point is the mystery of why the brilliant yellows in many of Vincent van Gogh’s paintings have been turning brown with age.
A recent study, carried out with an ultra high-tech process, using high intensity x-rays generated by a synchrotron at the ESRF, a center for the study of materials in France, has found the chemical reaction responsible for the unfortunate degradation.
It turns out that Van Gogh was fond of using the relatively new color, chrome yellow (also here), made from lead chromate. This is an inexpensive pigment that produces a bright orange-yellow (think school bus color), but is prone to darkening. Presumably, Van Gogh choose chrome yellow over the also relatively new cadmium colors (also here) because of their relative expense.
The mystery in the pronounced degree with which Van Gogh’s yellows have been turning brown is apparently due to his penchant for adding white paint, of a kind that contained barium and sulphur, to his yellow. The combination of the other materials accelerated the darkening of the chrome yellow.
Research is continuing into how to stop, and possibly even reverse, the changes to his paintings.
The Van Gogh Museum has for some time been studying his materials, and their sources, in an effort to better conserve the works, and conservators have encountered other uses of fugitive pigments (see my post on the Restoration of Van Gogh’s The Bedroom).
One of the paintings examined in the recent study was Van Gogh’s Bank of the Seine (above). The Van Gogh museum’s page for this painting also has an interesting video about their comparison of the work, and the techniques used, with that of his contemporary, Monet.