A REVEALING MOMENT

Van Gogh8217;s portrait of a peasant woman, concealed beneath another painting, has been reconstructed

Van Gogh8217;s portrait of a peasant woman, concealed beneath another painting, has been reconstructed

Using a thin beam of synchrotron X-rays generated by a particle accelerator, European scientists have reconstructed a portrait of a peasant woman painted by Vincent van Gogh that had been concealed beneath another painting for 121 years. The image, unveiled in a scientific journal, bears a striking resemblance to a series of sombre portraits the artist produced in the Dutch town of Nuenen, where he composed The Potato Eaters.

Conventional X-rays had revealed the rough outlines of the portrait, which Van Gogh covered 2 1/2 years later with a vibrant landscape of a flowering meadow after he moved to Paris. But the X-rays weren8217;t good at distinguishing between the many layers of paint and pigments made from heavy metals obscured colours from other elements.

8220;We get a very partial, fragmentary, colour-blind view,8221; said Joris Dik, a materials scientist and art historian at the Technical University of Delft in the Netherlands. So Dik and his colleagues took the painting, titled Patch of Grass, to a particle accelerator in Hamburg, Germany. The small but intense X-ray beam excited the atoms on the canvas, causing them to emit X-rays of their own that were captured by a florescence detector. It took two days to scan the roughly 7-by-7-inch portion of the meadow that masked the portrait.

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, sulphur 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 elements8212;mercury and antimony8212;to produce the outlines of the hidden portrait.

With the help of software, the team embarked on an elaborate version of painting by numbers. 8220;We colourised those two distributions according to the colour that the pigment would have had,8221; Dik said. Chemical analysis revealed the mercury was an ingredient of vermilion, the red pigment used to colour the woman8217;s lips, cheeks and forehead. Antimony was a component of Naples yellow, which was mixed with zinc white to highlight certain areas of the woman8217;s face, according to the report in the August issue of Analytical Chemistry.

Van Gogh often recycled his canvasses. Experts estimate that one-third of his early paintings hide other works, which may be ripe for new analysis.
-Karen Kaplan