Future-proofing the past

What would happen to a famous painting if curators were to suddenly withdraw all care and attention? How many generations would come and go before, say, Van Gogh’s Sunflowers merged into a dirty smudge – and would that necessarily be a bad thing? These are among questions I put to Ella Hendriks at the Van Gogh Museum (VGM) in Amsterdam, where she is head of conservation. “I don’t think that we can know how long a painting would last,” she explains softly from behind her desk in a smart, carpeted office. “When do you decide that it’s gone?”

Paint on a canvas may seem rock-hard and static, but in fact it is a highly mobile system even many decades after the paint has dried. Back in the 19th century, people were more interested in restoring paintings to their original condition, but today such intervention is deemed futile because curators know that paintings change from the moment that they leave the easel. “There’s a lot going on in the paint layers,” says Hendriks. “Today we try to preserve the equilibrium.”

Synchrotron synergy

Synchrotrons are helping to elucidate these microscopic processes, which take place in layers too thin to be resolved easily by standard laboratory microscopes. The way that paint, particularly lake red, fades is one actively researched area. Last year, a microscopic fragment of paint from Van Gogh’s View of Arles with Irises was subjected to X-ray diffraction at the ESRF, revealing the reaction in lead chromate responsible for the discolouration of yellow pigment under UV illumination – reinforcing the need to keep sunlight at bay. X-ray imaging at DESY in Hamburg had previously revealed a portrait beneath Van Gogh’s Patch of Grass, property of the Kröller-Müller Museum in Otterlo, but this was the first collaboration between the VGM and the synchrotron community.

A deeper understanding of ageing processes raises questions about the extent that the knowledge should be used to preserve a painting. Take the climate cases used in the VGM to keep masterpieces in stable ambient conditions. Curators could remove all of the oxygen from the cases so that certain undesirable reactions in the paint stopped taking place, but the long-term consequences of this aren’t known.
In fact, Hendriks says some of the problems that conservators are addressing now are due to the fact that paintings have been treated in the past. “People act with the best of intentions, but there is always a danger of over-reacting by applying new techniques that may have a detrimental long-term effect.”

In the 19th century, one restorer thought he had found a way to get round the task of revitalising old varnish by holding a painting over a bathtub of alcoholic vapour. The varnish regenerated and the microcracks in it disappeared, as planned, but the vapours also softened up the paint layers and ultimately ruined the work. In the 1960s, scientists came up with synthetic varnishes that they claimed did not yellow over time, but it turned out that these new products were oblivious to some of the solvents that had been developed to remove varnishes. Even something as apparently innocuous as strapping batons to the back of a painted wooden panel to strengthen it can, given enough time, introduce forces that cause the panel to split.

Tests show the dulling effect of paint varnish (Credit: M. Chalmers).

As a conservator, Hendriks says that her job is to intervene in the artworks as little as possible, although she admits that the consequences of this minimalist approach are also unknown. Even handling an unvarnished canvas without gloves could leave her DNA on the surface, making it harder to identify that of the artist.

Besides, Van Gogh paintings were subjected to a rigorous campaign of treatment in 1926–1933. Most were varnished at this time, whereas the artist favoured a matt surface, and some were retouched by adding new paint. Many of the canvases have also suffered more serious structural effects due to wax-lining – the process of ironing a second canvas onto the back of a painting to make it more sturdy. Favoured until just a few decades ago, over time the wax becomes a permanent part of the structure that causes the painting to darken. Yet, Hendriks points out, nobody knows what condition the paintings would be in had they not been wax-lined.

A major appeal of an old painting, however, stems from the very things that mark its demise: networks of microcracks in the varnish, subtle browning and softening of colours, and even bulk damage that tells the story behind the work. Distinctive cracks in some Van Gogh paintings formed when he used to roll up a canvas and send it to his art-dealer brother in Paris, and Hendriks occasionally comes across one of the artist’s hairs or a fingernail imprint while studying a specimen. Ageing is also an important mark of provenance and authenticity.

Modern culture

Conservators don’t know what to expect from more modern works of art because there is no reference of ageing. “Freedom of expression has taken the place of craftmanship in some areas,” says ESRF user Joris Dik of the Technical University of Delft in the Netherlands. “There is an artist who spreads peanut butter over the floor: how do you preserve that?”

Dik, who’s work scanning Van Gogh paintings with a mobile X-ray source helped lead to the recent collaboration between the VGM and the ESRF, envisages that paintings will one day be protected indefinitely by coating them with self-healing materials. “First we need to understand the degradation mechanisms, then the reaction kinetics, and finally what can be done to halt the deterioration.”

Meanwhile, the conservation department at the VGM is pondering the effects of rock music on its 300 or so masterpieces due to open-air concerts on the nearby Museumplein. Hendriks is also working out how to deal with tiny white blobs produced when zinc white and lead white pigment particles turn into metal soaps over time. “There’s still a gap between identifying the mechanisms and knowing how we should use that knowledge,” says Hendriks. “There is a lot of constructive discussion between conservators, and approaches may vary in different countries.”

As to why we should be preserving these splashes of pigment on pieces of cloth in the first place, Hendriks directs me to the 5–10 thousand people who visit the VGM every day. “I think Van Gogh has a special significance to many people,” says Hendriks after a pause. “To each person it’s different, but if you imagine it wasn’t there, the world would be a much poorer place.”

Palpable genius: Van Gogh’s Wheatfield under a Cloudy Sky reveals its depth (Credit: M. Chalmers).

Naked art’s hidden layers
The work going on in museum research departments worldwide goes against the stereotype that art and science are opposites. Conservators have science as part of their training and act as a bridge between the art and other worlds. The fact that their work is now turning to synchrotrons is a natural step for conservators developing new ways to keep paintings intact.

Surveying visitor opinion, staff at the VGM found that the public want to know more about the conservation work and to get a peek behind the scenes. Having got up close and personal with an 1890 Van Gogh oil painting in a studio (pictured), I can strongly recommend it. As my eyes scanned the green and blue paint laid bare on a table without protective glass or frame, the peaks and troughs carved by the artist’s individual strokes brought the canvas alive. A splatter of red blobs from a distance captures the essence of poppies swaying in the breeze.

“The difference between art and science is more about different languages, organisation and traditions, rather than the interest and curiosity of people involved,” says Joris Dik of the Technical University of Delft in the Netherlands. “Art history has always been part of the humanities, and so is more aligned with literary techniques than archaeological ones, unlike palaeontology, which has traditionally been part of the sciences.”

When big museums opened up research departments early last century, conservation science was born and in the late 1920s it proved its worth in the Netherlands during a court case concerning the famous “Wacker” series of Van Gogh forgeries. This was the first time that chemical analysis of paint samples and X-rays were used as evidence in a court trial, which had brought the art world and connoisseurship into disrepute.

This article appeared in ESRFnews, June 2011. 

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