Science: Open-art surgery

Unless the art doctors get there soon, Damien Hirst's shark will droop. Norman Miller meets the conservators who operate at the interface between art and science

SO IS Damien Hirst worried? Not only does the publicity-loving not-so-enfant terrible of BritArt have to cope with one of his famous fishy creations dismally failing to reach its reserve price at auction, but now his shark's going soft too. It's time to call in the art conservators.

If you thought art conservation was just public school types squinting at an old canvas and gibbering on about brush strokes and the artist's use of gestural impasto, think again. The modern conservator is more likely to be messing about with X-rays, ultraviolet and infra-red, electron microscopy, mass spectrometry and gas chromatography. For this is where art and science truly meet.

X-rays and infra-red can peer through the top layer of a work to reveal earlier versions, changes made by the artist, or work by previous restorers. But if you want to work out the precise constituents of a work of art - be it the pigment on a painting or the metal in a piece of jewellery - then you enter the realm of elemental analysis.

Elemental analysis relies on the fact that materials react in different ways when they are excited by radiation - such as infra-red, ultraviolet and X-rays - an approach which Sarah Holt, a conservation expert at Birkbeck College, London, describes as "a one-step direct technique" for working out what a sample from an artwork contains.

The simplest form of elemental analysis involves just looking at a sample under an ordinary microscope to observe its colour. A blue or pink tinge will suggest that copper is present, while a mottled grey colour indicates lead. Simple microscopic analysis was enough to detect lampblack (soot collected from a smoky flame) in the black paint on the dark dress worn by Hans Holbein's Lady With A Squirrel And A Starling (1526-28).

One of the most favoured forms of elemental analysis is energy-dispersive X-ray analysis (EDX), for which only a tiny sample is required from the work - so minute that it would barely be visible without a microscope. The sample is placed in the chamber of a scanning electron microscope and a beam of X-rays is focussed on it. The different ways in which the elements in the sample react to the X-ray bombardment provides an output reading in the form of peaks and troughs. EDX is particularly useful for working out the composition of metal alloys - for example, in identifying ancient Greek jewellery, which is known to have been made from specific alloy compositions.

National Gallery experts used EDX to detect a chalk layer beneath the pigment on Aelbert Cuyp's 17th-century work The Large Dort. Because chalk affects the colour of the pigment it is mixed with, as well as the strength of its chemical bonds, a conservator would need to establish whether Cuyp had used it or not. In analysing the previously mentioned Holbein, EDX identified the components in the paint used for the leaves as lead-tin yellow combined with verdigris, linseed oil and pine resin (this last was used to provide translucency and gloss). In the days of the Old Masters, artists needed to be chemists of a sort, mixing up a wide range of materials to get the colour or quality they wanted for paint or varnish, taking into account the depth of colour, drying times and transparency.

After the elements have been identified, there is the need to find out about the precise structure of a material in a sample. For this, conservators turn to X-ray diffraction (XRD). This involves taking another small sample of paint (about a pinhead's- worth), placing it in a special camera, and firing an X-ray beam at it from different angles for several hours to observe how the crystal planes within each constituent element are diffracted by the rays. The film in the camera is then developed to give an XRD pattern (a series of lines of varying intensity), which can be measured and compared to patterns from samples of known materials.

UV light can also be used to gather information about a painting. Observing how different areas fluoresce reveals previous restoration efforts (good or bad), as well as helping to identify other elements, such as the kind of sealant used. On ceramics, meanwhile, a technique called thermal luminescence (TL) can be used to date a piece by measuring radiation levels. The radioactive decay of elements within the clay (plus a contribution from background radiation) gives rise to an age-dependent reading. This can be measured by heating powder from the object, and producing a "glow-curve" by causing it to glow with light which is invisible to the naked eye but detectable by sensitive equipment. The more time that has elapsed since the piece was fired, the more intense the signal.

The shape of a glow-curve can also reveal information about the kinds of clay used for a piece, and whether restoration has been attempted in the past. But TL testing alone cannot always pick up a fake. Five years ago, experts came across a pott-ery horse which they knew was not a genuine T'ang period piece, since other tests had picked up evidence of the presence of modern fluids in the fabric of the pot - yet a TL test had suggested that the horse was as old as was claimed. Careful examination revealed that forgers had deliberately set out to fool modern technology by putting fragments of ancient unglazed clay in the only sections of the horse that could be easily drilled for samples (the base and the firing hole).

The lesson is that while hi-tech machinery is a great asset, it can't replace expert knowledge. As another Birkbeck College conservator, Anna Bennett, says: "It won't characterise your material for you." For example, two pigments may be based on the same element but look totally different. Azurite and malachite are both types of copper carbonate - but one is blue and the other green.

Bennett is dismissive of the commonly held view that most conservation work is about patching up Old Master canvases, or "easel paintings" as they're known in the trade. For her, poring over a Poussin identifying pigments and varnishes is very old hat. "You'll never find a new pigment," she says, showing me a long list which details all those used in paintings, with dates of when they were used (or discarded) by artists. The dates range from vaguely ancient ("before 1300") for materials like azurite, cinnabar and indigo, to modern and specific ("1964 Benzimidazolones").

For Bennett, the real analytical challenges lie outside painting, and she is more animated when discussing 18th-century furnishings, Venetian glass and Roman statues. She points out that it was scientific analysis that revealed the fact that Roman statues were originally painted in a wide range of colours, although they were commonly thought to be white originally. She explains how analysis of trace elements in old Venetian glass objects has shown that the glass originated in Africa, and gives clues to the trading routes used.

Tests can now tell a restorer what was on the walls of old buildings, in sharp contrast to the days when some National Trust committee "just picked some Colefax & Fowler wallpaper that looked right for the time". In 1989, when the 17th-century Sussex house Uppark was partially destroyed by a fire, the Trust relied on the conservators to find out precisely which plasters and paints had been used in the original building.

The most famous recent example of restoration work is probably that involving the Mary Rose, the Tudor warship which was raised from its watery grave in the Eighties. Bennett describes how modern science preserved its fragile timbers. If the ship had been allowed to dry out normally, the contraction caused as the timbers shrank would have destroyed it. Conservators, therefore, first pumped in a substance called polyethylene glycol (PEG) and then freeze-dried it. The process forced the water out of the wood and replaced it with PEG - this simultaneously dried out and strengthened the timbers.

With the current trend for using organic objects in art works, conservation expertise has become more complicated. Formaldehyde is a Damien Hirst trademark, but while it has helped to keep 200-year-old body parts in the Royal College of Medicine in excellent condition, the formulation used by Hirst to suspend his shark is not quite cutting the mustard. Unless a new formulation is found soon, the shark will droop.

Dealing with modern art presents new challenges for the likes of Tate Gallery conservator Derek Pullen. Whether it's in the form of Sixties chocolate painting or Anthony Gormley's lead-cased objects containing eggs, new materials present new problems. With Gormley's work, for example, substances produced by the decaying eggs began to make the lead's soldering split.

Naum Gabo, one of the century's leading sculptors, created pieces out of certain types of plastic which now, a few decades later, are beginning to warp and discolour. The conservation challenge here is to work out how to lower the acid content in the plastics. But can such a procedure be ethical? If an artist has chosen to make a piece in a material which they know is not going to last, should it be conserved? Do the values of posterity and ownership clash with artistic intent?

Pullen's aim, he says, is to "preserve the ability to show work in its original way", and to that end artists are often asked to provide conservators with detailed information of how they have made a piece. In fact, artists will now often call up and ask about the stability of materials before using them. "Technically, most things are possible," says Pullen, though he admits to sometimes acknowledging defeat - as in the case of a work made in felt by the German artist Joseph Beuys, which suffered a nasty attack by moths.

"Technology is always moving on," he says. "Even a few years ago the idea of using oxygen-free showcases to slow down deterioration of organic objects seemed far-fetched." Now nitrogen is often used in the preservation of documents, including the American Declaration of Independence and some priceless Egyptian texts.

Preserving film is now one of the biggest issues facing conservators, says Pullen: celluloid nitrate and celluloid acetate are not the most stable of materials. Yet celluloid acetate is still being used, because the quality of the image it produces is of more importance to the film industry than longevity.

Pullen believes that saving our film heritage is a concern not just for the conservators. "We appear to value the past," he says, "but we're in danger of losing large chunks of first-hand evidence in the form of film records of the 20th century. There is simply too much material and not enough resources - machines, time and money - to copy on to more stable stock, even if that were available."

Pullen agrees with Bennett that the main challenges in conservation are in the field of objects other than paintings. "We are at an interface with objects," he says, "where chemistry and physics underpin most conservation decisions." It is an irony, therefore, that most people come into conservation from an art history rather than a scientific background, though Birkbeck plans to offer a part-time MSc in Art Conservation, starting in the year 2000, to help put this right.

Anna Bennett laughs when she is asked whether Birkbeck College is equipped with all the hi-tech gizmos we had discussed. Even though electron microscopes and X-ray diffraction equipment are constantly pressed into the service of art conservation, they remain - physically, at least - in the domain of the scientists. Bennett and the others queue up alongside nuclear chemists in the science labs for time on the machines.

Still, any bridge between art and science must surely be a good thing. Bennett delights in telling me that one of the National Gallery's best- selling postcards of recent times was not of a painting, but a photo-micrograph of a pigment sample made by the gallery's conservators, a beautiful and complex insight into the very nature of art. !