Scientists at the research laboratory of the Museums of France in Paris compared the painting with nine of the 70 works accredited to Van Gogh during his time at Auvers. However, they were not allowed to remove samples from the painting, and could not use the lab's synchrotron X-ray source since radiation can sometimes heat organic matter. "Van Gogh used organic matter such as geranium for colouring," explains Elizabeth Martin, a scientist at the lab.

Instead, the team used a technique called microfluorescence, in which a beam of X-rays less than 1 mm wide was used to reveal the spectrum of most of the elements in the pigments. Unlike X-ray diffraction methods, microfluorescence does not destroy the surface of the painting. The researchers also used radiography to show that the canvas matched the kind Van Gogh used during his period at Auvers. And they found that the way in which the paint was applied was also consistent with Van Gogh's style. Forgers often build up more layers of paint as they need several attempts to reproduce the style of the original.

Finally, the painting was examined by microscope. "This analysis gave very interesting clues," says Martin. As with the other nine studied, the canvas showed markings where Van Gogh had stacked up his paintings on his bed before the oil was completely dry. "We found nothing that was incompatible with the painting being a Van Gogh," says Martin. "Now it's for the art historians, who are the specialists of Van Gogh, to make their conclusions."