Paintings have been examined with X-rays for years, but sometimes an old technique can be used in a new way — and reveal new clues about old mysteries.
Since 1974, "Still Life with Meadow Flowers and Roses" has been hung in the Kroeller-Mueller Museum. For decades art historians debated whether it was painted by Van Gogh or someone else.
Joris Dik and his team at the Delft University of Technology decided to use X-rays to examine the painting. Back in the late 1990s, X-rays were used to reveal an image underneath the still life: two men wrestling. But there were limitations. Van Gogh had written his brother Theo about the painting of the wrestlers, but it was not clear that was the one — there just wasn't enough detail. The lack of detail, and some differences between the still life and Van Gogh's other works, got the still life bumped off the official list of Van Gogh paintings in 2003.
One problem is that X-rays are absorbed by heavy metals such as lead. Nineteenth-century paintings use lead in the white pigment. X-ray a painting and you'll see where the white paint is, but that will block anything underneath it.
To get around this, Dik decided to rely on another phenomenon: fluorescence. The technique is called Macro Scanning X-ray Fluorescence Spectrometry, or MA-XRF. Fluorescence happens when X-rays (or any other electromagnetic radiation) hits an atom or molecule. The target atom will absorb the energy and re-emit the radiation, at a lower wavelength, and each element radiates at a different wavelength.
"In nineteenth century paintings you can find almost the whole periodic table," Dik told Discovery News. "But before those couldn't be visualized." Mercury, for instance, fluoresces at a characteristic wavelength and was used in cinnabar, which makes vermillion paint. "It basically gives us color vision."
The same principle is behind a fluorescent light: light emitted by the gases in the bulb is actually ultraviolet, but it hits a substance on the inside of the glass that re-emits it in longer wavelengths people can see.
The pigments in the paintings fluoresce at X-ray wavelengths, not visible ones. But with an imaging device one can see them and deduce what elements are in the pigment. Knowing that, it's possible to guess what color was used.
When Dik's team looked at "Still Life With Meadow Flowers and Roses," they were able to see not only the elements in the pigments, but the structure of the brush strokes. Coupled with the letter Van Gogh wrote, it is very strong evidence.
Dik said he wants to apply this technique to other paintings, in New York's Metropolitan Museum, the National Gallery in Washington, D.C. and the Museum of Modern Art.
The apparatus for the scans has another big advantage over earlier designs: it's portable. That means the paintings can be examined where they are. Dik says the university is working in conjunction with a company to build a commercial version of the scanner. "The technology we developed is now turning into something practical," he said.
Photo: Detail of the Van Gogh painting "Still Life With Meadow Flowers and Roses."
Credit: Wikimedia Commons