Unlocking the molecular secrets of Van Gogh's work

A multi-million euro study of Vincent van Gogh's work casts new light on his contemporary influences.

The austere basement of Amsterdam's Van Gogh Museum seems an unlikely place to conduct breakthrough research. Racks filled with boxes and glass plates clutter the floor. The space, covered by a suspended ceiling, is completely devoid of daylight. Conservator Devi Ormond has created a makeshift workshop for herself since the museum's proper conservation facilities closed down for renovation. She has spent the last weeks here, day in, day out, in the company of a microscope, a laptop and a selection of masterpieces by Dutch painter Vincent van Gogh (1853-1890).

On a recent visit, Ormond showed a small and dark still-life of a couple of bottles, painted by Van Gogh in the Dutch town of Nuenen in 1884. Ormond cast a light over the surface of the paint as she stared through a microscope lens that magnified what she saw by a factor of 40. "Conservators love this," she beamed. "It feels like deep-sea diving. It's like being carried off to another world. Look at all the fine details you can discern."

A collaborative project

Ormond is one of the 30 researchers participating in ‘Van Gogh's studio practice’: a collaborative project between the museum, oil company Shell and the Dutch Institute for Cultural Heritage (ICN). The project's most distinctive trait is its multidisciplinary character. Van Gogh's studio practice brings together conservators, art historians, scientists and chemists. "That exchange has raised new questions," said Marije Vellekoop, who leads the project. "Hopefully, those questions will lead to new answers."

The question central to the research is the relationship between Van Gogh's practices and those of his contemporaries. Was he influenced by artists in his circle of friends for instance? And did they use the same materials? The results will be presented at a symposium and a major exposition in the Van Gogh Museum in 2012. Until then, research reports will be posted on a dedicated (Dutch) weblog, which was launched on Thursday.

Ormond has recently been absorbed in the work of Anton van Rappard (1858-1892), a fellow painter Van Gogh met in 1880 and with whom he remained friends for five years, until they had a falling out over The Potato Eaters. "I wanted to know if these two painters influenced each other," Ormond said. "Van Rappard's choice of colours was dark, like Van Gogh's was in Nuenen. Perhaps they borrowed tricks from each other?"

Ormond placed a tiny Van Rappard painting of a weaver in a dark room under her microscope. "This painting was made in the same year as the still-life by Van Gogh," she said. "Do you see that dark, transparent primer? Van Gogh used the exact same one." Ormond discovered that the shadows both artists used in their work are not black, but rich in Prussian blue. She suspects both painted on the same type of canvas as well. Ormond pointed out a number of X-rays of the two paintings hung on a display. "I did a thread-count on both cloths," She said. "The numbers match. I suspect that it is a commercially produced fabric, which the painters purchased from the same supplier."

X-ray gun

Luc Megens, a chemical researcher at the ICN, confirmed Ormond's suspicions. He spent a lot of time in the Van Gogh Museum's conservation studio in recent months with his portable XRF machine. This pistol-like sensor can analyse the chemical composition of different paints by their wavelengths. He pointed his gun at the surface of the paint on Van Rappard's picture of the weaver. A readout on his laptop showed two telltale peaks. "Ah, it contains iron," Megens said. "That could indicate Prussian blue: it contains ferrocyanide." The other peak betrayed the presence of lead, which Megens suspected could mean a coat of lead white primer had been applied.

The advantage of the XRF-method, Megens explained, is that it does not damage the painting under scrutiny. A drawback is that it scans all paints at once, making it is impossible to distinguish between different layers. To find out their specific composition, it is still necessary to take minute paint samples. Muriel Geldof, another ICN researcher, is responsible for that part of the research process.

The sample Geldof cut out from the Van Rappard measured a mere 0.2 millimetres, barely visible to the naked eye. Under her optical microscope, which could enlarge it as much as a thousand times, it bore some resemblance to a piece of sushi. A thick bit of white primer was topped by a thinner coat of darker paint. Geldof zoomed in on the dark paint until suddenly, red, yellow and blue dots burst into view. "Like Van Gogh, Van Rappard mixed primary colours into his paint," Geldof concluded. "In the 19th century, scientific interest in colour theories began to take hold. That left its mark on the work of these two painters."

But for a definitive analysis of the composition of the pigments, the paint monster would have to be carried to Shell's Technology Centre, in a far-flung part of Amsterdam. Shell supports the Van Gogh Museum financially, but also in kind, by letting it use its state-of-the-art electron microscopes for its research. These devices, capable of magnifying objects by as much as a million times, allow researchers to study paints at the atomic level. Shell has also dedicated a lot of man hours to the study. The petrochemical giant was unable to say how much it had spent on the project exactly, but estimated total costs ran into the millions of euros.

The molecular level

Shell employees are very proud to be working with the Van Gogh Museum. Kees Mensch, a retired researcher, has remained on the job just because he likes the project so much, often working the graveyard shift when expensive equipment is not in use by Shell's other employees. "I am glad I have something useful to do," he laughed from behind his safety glasses.

As the Van Rappard paint speck was placed under the electron microscope, Mensch's display lit up in different shades of grey. The sample had been magnified so much, only an abstract pattern of dots and blurs remained visible. For Muriel Geldof, dressed in a white lab coat, one glance was enough though. "Chrome yellow!" she exclaimed. "We see the same in Van Gogh's work. This means they did use the same pallet of colours."

The electron microscope also determined the contents of the primer: chalk and lead white. "The same Van Gogh used," Geldof said. "Perhaps Van Rappard borrowed some off Van Gogh when they went out together. Or perhaps they bought it at the same art supplies store." Devi Ormond smiled. This is what she suspected all along. But now it had finally been proven.