Art historians have been using x-rays to probe artworks hidden underneath other paintings for many years now. However Joris Dik and Koen Janssens made a step forward by combining science with art. They discovered a new method of finding hidden artwork through an x-ray technique that has never before been applied to a painting. The first is a materials scientist from Delft University and the latter is a chemist from the University of Antwerp in Belgium.

Because he was very poor, Vincent Van Gogh is known to have reused his canvases. A peasant woman's face was hidden behind the work Patch of Grass, completed by Van Gogh in Paris in 1887. The woman’s identity is not known. Experts believe that approximately third of his works hide a second painting underneath.

Still the painting may have been made during Van Gogh’s stay in Nuenen, Holland, in the early years of his career as a painter, sometime between 1884 and 1885. This was a very dark period as far as his work is concerned as he used mainly earth tones, particularly dark brown, and he showed no sign of developing the vivid coloration that distinguished his most famous works.

High-intensity x-rays were used to unveil the hidden painting in order to compile a two-dimensional map of the metallic atoms on the painting underneath. Scanning a 7-inch square of the larger painting took two full days. The combination of how the elements mercury and antimony (from specific paint pigments) were distributed provided information on the color of the portrait.

Joris Dik and Koen Janssens published their scientific paper online in the journal Analytical Chemistry.