Click to enlarge. Credit: DELFT UNIV. OF TECHNOLOGY

An unknown Vincent van Gogh painting of a woman's head has been revealed with X-ray technology. The painting is thought to have been made in 1884–85, during a period in which he painted several portraits of peasants in the Dutch village of Nuenen. The image was hidden beneath Patch of Grass, an unrelated landscape that van Gogh painted a year or two later when living in Paris.

Earlier X-ray studies revealed a faint, blurry shadow of a figure. But Joris Dik of the Delft University of Technology in the Netherlands and his colleagues have extracted a much sharper image using the Deutsches Elektronen-Synchrotron (DESY) in Hamburg, Germany (J. Dik et al. Anal. Chem. doi:10.1021/ac800965g; 2008). The synchrotron's X-ray beam excites secondary X-rays from elements in the sample at characteristic wavelengths. The researchers mapped the distributions of cobalt, arsenic, lead and other metals in the hidden paint layers — all well-known components of pigments that were available at the time. Although the study did not identify all the pigments in the picture, it enabled the researchers to create the partial colour reconstruction shown here.

Van Gogh often re-used old canvases, partly in an effort to save money. Dik's team speculates that he took the portrait with him to Paris, where it would have seemed sombre and unfashionable in comparison to the Impressionists' works, and so he decided to paint a brighter, more commercial floral scene over it.