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Preserving Van Gogh's magic
Works by Vincent van Gogh and other Impressionist masters fade over time, but analysing tiny paint samples can help experts find ways to preserve them for future generations.
April 11, 2008
by WENDEL BROERE
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"All the colours that Impressionism has made fashionable are unstable, all the more reason to boldly use them too raw, time will only soften them too much." — Vincent van Gogh, April 1888.
Impressionist painter Vincent Van Gogh saw the colours on his paintings fade during his own brief lifetime – a process that continues to this day, despite conservation efforts. Van Gogh was a self-taught painter who moved to Paris in 1886 to pursue the dream of becoming a professional artist. His years in France were full of experimentation as he explored a variety of materials and painting techniques, some of which made his works susceptible to rapid ageing. That experimentation complicates the job of art historians and museum conservators as they try to preserve his work.
But joint research by the Van Gogh Museum in Amsterdam and Shell is shedding fresh light on the paint he used and how he applied it – information that could help experts keep his works from deteriorating even further. By scrutinising paint samples, curators and Shell scientists are also getting a better understanding of what Van Gogh’s masterpieces originally looked like.
“If we can discover what materials were used and how, we can sometimes understand how artists got those wonderful effects you see on a painting and explain better what might have changed since it was made,” says Aviva Burnstock, head of the Department of Conservation and Technology at the Courtauld Institute of the University of London.
Researchers have studied 97 paintings Van Gogh made between 1886 and 1888, a period when little is known about his techniques because he wrote few letters. One approach analyses paint fragments with powerful electron microscopes, identifying chemical components by bombarding the samples with electrons. The first phase of research used paint fragments of a few square millimeters containing several pigments, which made it difficult to interpret the results.
Shell researcher Ralph Haswell took the study a step further by borrowing a technique first used in the semiconductor industry. The Shell team cut paint fragments into sections as small as one thousandth the width of a human hair using a beam of high-energy ions. That allowed more precise readings from each fragment. Full results from the study won’t be published until 2011, but findings are trickling in already.
For example, Shell researchers, who normally use electron microscopes to examine catalysts, found a white pigment called barium sulphate in the first layer of paint in an early study of one of Van Gogh's famous sunflower paintings. Van Gogh probably used barium sulphate to dilute expensive lead white tube paint, a new product in the 19th century. Traces of the element strontium in the samples shows the barium sulphate was of natural origin, perhaps collected by Van Gogh himself. “If we can determine the precise ratio of strontium to barium, we could determine from what quarry he got his barium sulphate,” Haswell says.
Other research provides a clue. Menilite, a reddish-brown mineral substance also found in the first layer of paint, could indicate Van Gogh’s ingredients came from a quarry north of Paris. Such evidence can help art historians, particularly as they try to verify the authenticity of canvases thought to have been painted by Van Gogh.
The museum’s research also gives insight into Van Gogh’s technique. “One of the very surprising findings is that we think of Van Gogh as a very spontaneous painter who painted very quickly, setting down his brushstrokes in one go,” says Ella Hendriks, Head of Conservation at the Van Gogh Museum. “But quite often it turns out that he started out with a rather detailed sketch.” Infrared photographs of his paintings show Van Gogh sometimes used a perspective frame and fine sketches before picking up his brushes.
Once he began to paint, he worked rapidly. That is clear, for instance, in the cracks in flower petals in the uppermost layer of paint in the still life “Basket with pansies on a stool” (1887). Van Gogh used a mixture of zinc white and other ingredients to hide an earlier painting on the same canvas. Zinc white dries slowly – something art historians say Van Gogh and his paint suppliers would have known – while the violet paint on top contains cobalt oxide, a fast-drying blue colour. The cracks appeared because the outer layer dried faster.
Restorers have learned to be careful when using common cleansers such as mild organic solvents and water. Take the painting “Agostina Segatori in the Café du Tambourin” (1887), depicting a former model of fellow painters Camille Corot and Edgar Degas. Van Gogh used red paint thickened with starch, which made it soluble and prone to damage if cleaned. The red was originally bright crimson, but has now faded to pink.
The museum’s growing knowledge about Van Gogh’s paintings has sparked increased requests to verify the authenticity of supposed works by the Dutch master. The museum receives some 300 requests each year. Last year a six-month study of the painting “Portrait of a Man”, previously attributed to Van Gogh, found it was painted by an unknown artist.
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