Painted-over Portrait Probed

An international research team has used synchrotron x-rays from a particle accelerator to reveal the portrait of a woman hidden beneath Vincent Van Gogh's painting "Patch of Grass" for 121 years.

It's well known that Van Gogh often recycled his canvases, painting over older works. Experts estimate that about one-third of his early paintings conceal other compositions. In the case of "Patch of Grass," conventional x-ray radiography previously revealed a vague outline of a head, while the new technique based on synchrotron radiation-induced x-ray fluorescence spectroscopy revealed much greater detail.

Synchrotron radiation-induced x-ray fluorescence (SR-XRF) spectroscopy has revealed a detailed portrait of a women hidden beneath Vincent Van Gogh's "Patch of Grass" painting. Previous attempts with conventional x-ray radiography revealed only the vague outline of a head. (Image: University of Antwerp)

The new technique was implemented by Delft University of Technology materials expert and art historian Dr. Joris Dik and University of Antwerp chemistry professor Koen Janssens, working with experts from the Deutches Elecktronen Synchrotron (DESY) in Hamburg, Germany, and the Kröller-Müller Museum in Otterlo, Netherlands, which owns the painting.

Over the course of two days, the painting was subjected to an intense but very small x-ray bundle of synchrotron radiation from DORIS III, a storage ring for charged particles, and the fluorescence of the layers of paint measured. A major advantage of the new technique over previous methods is that the measured fluorescence is specific to each chemical element, so each type of atom, such as lead or mercury, and individual paint pigments can be charted separately.

University of Antwerp analytical chemist Koen Janssens adjusts the alignment of the Van Gogh painting Patch of Grass in the x-ray fluorescence spectrometer at beamline L of the DORIS III synchrotron facility in Hamburg, Germany. (Image ©DESY Hamburg)

The benefit of using synchrotron radiation is that the upper layers of paint distort the measurements to a lesser degree. Moreover, the speed of measurement is high, which allows relatively large areas to be visualized, the researchers said.

The measurements enabled researchers to reconstruct the concealed painting in unparalleled detail, enabling art historians to better understand the evolution of Van Gogh's work. The combination of the distribution of the elements mercury and antimony (from specific paint pigments) provided a "color photo" of the portrait which had been painted over. Additional investigations performed at the European Synchrotron Radiation Facility in Grenoble, France, revealed the presence of the pigments Naples' yellow (lead antimonate, yellow-brown) and vermillion (mercury sulphide, red), used by Van Gogh to paint the portrait.

The new technique is expected to pave the way for research into many other concealed paintings, including more by Van Gogh.

For more information, visit: www.tudelft.nl or www.vangogh.ua.ac.be