"Patch of Grass" was painted by Van Gogh in Paris in 1887. Behind the painting is a portrait of a woman.

A previously unknown portrait of a woman by Vincent van Gogh has been revealed in a high-tech look beneath another of his paintings, it was announced today.

Scientists used a new technique to peer beneath the paint of van Gogh's "Patch of Grass." Already it was known there was something there, likely a portrait of some sort. Van Gogh was known to paint over his work, perhaps as much as a third of the time.

Behind the painting, done mostly in greens and blues, is a portrait of a woman rendered in browns and reds.

The new technique is based on "synchrotron radiation induced X-ray fluorescence spectroscopy" and is said to be an improvement on X-ray radiography, which has been used to reveal concealed layers of other famous paintings. The new method measures chemicals in the pigments. Specifically, mercury and the element antimony were useful in revealing the woman's face.

The work was done by researchers at Delft University of Technology in the the Netherlands and the University of Antwerp in Belgium, along with help from other institutions.

"Patch of Grass" was painted by van Gogh in Paris in 1887 and is owned by the Kröller-Müller Museum.

The reconstruction enables art historians to understand the evolution of van Gogh’s work better, the researchers said in a statement. And the new technique is expected to pave the way for research into many other concealed paintings.