HAMBURG, Germany—European scientists have used synchroton X-rays generated by a particle accelerator to reconstruct a van Gogh portrait of a peasant woman concealed underneath a later painting of his, the Los Angeles Times reports. The image was unveiled in a scientific journal published today.

Conventional X-rays had suggested the outlines of a portrait hidden beneath Patch of Grass, an 1887 painting of a flowering meadow, but the X-rays weren't able to fully distinguish between the multiple layers of paint, and pigments from heavy metals obscured many of the colors. Joris Dik, a materials scientist and art historian at the Technical University of Delft in the Netherlands, and his colleagues took the work to a particle accelerator in Hamburg, Germany.

The intense X-ray beam excited the atoms in the painting and caused them to emit their own X-rays, which were captured by a florescence detector. Each element in the painting had its own X-ray signature, allowing the scientists to identify the distribution of metals in the layers of paint and construct a three-dimensional model of the whole work. They then peeled off the top layers and reconstructed the hidden painting on the computer by colorizing the distributions of mercury and antimony in the bottom layer. The result resembles a series of somber portraits van Gogh painted in the Dutch town of Nuenen, where he also created The Potato Eaters in 1885.