Experts say as many as one-third of Vincent Van Gogh's paintings may conceal earlier works that the artist chose to paint over. Now one of those hidden works has been revealed -- the somber portrait of a peasant woman concealed beneath the sunny impressionistic colors of "Patch of Grass," which was painted in Paris in 1887.
Conventional x-rays had revealed the presence of an earlier painting, but could not distinguish the colors in the image. So an international team of researchers took it to DESY, the Deutsches Elektronen-Synchrotron, in Hamburg, where it was exposed to a powerful beam of X-rays generated by a particle accelerator. The X-rays caused various elements in the pigments to fluoresce, enabling experts to recreate the colors.
According to an account in today's Los Angeles Times:
Since each element in the painting had its own X-ray signature, the scientists were able to identify the distribution of metals in the various layers of paint and construct a three-dimensional model of the work. Then the team peeled off the layers one by one.
The top layer consisted of paints made with zinc, barium, sulfur and other elements. Behind that they found a uniform distribution of lead, which was used as a primer to hide the portrait and prepare the canvas for a new painting. Once that was removed, they combined the distributions of two more elements -- mercury and antimony -- to produce the outlines of the hidden portrait.
Then, with the help of computer software, the team embarked on an elaborate version of painting by numbers.
"We colorized those two distributions according to the color that the pigment would have had," Dik said.
Chemical analysis revealed that the mercury was an ingredient of vermilion, the red pigment used to color the woman's lips, cheeks and forehead. Antimony was a component of Naples yellow, which was mixed with zinc white paint to highlight certain areas of the woman's face, according to the report in the August issue of Analytical Chemistry.
For more details see this press release from lightsources.org.
The same technique was used to uncover a 10th-century copy of treatises by Archimedes, whose parchment had been written over as a prayer book by a Christian monk. This experimental scanning was performed at the Stanford Synchrotron Radiation Laboratory. You can read all about the Archimedes Palimpsest here.
