Engineers come to art's rescue

New project aims to give cracked London sculpture a second chance.

Moore's fans are hoping his sculpture will stand once again. Credit: Reproduced with permission of the Henry Moore Foundation

In a storage yard in London’s Kensington Gardens sit seven pieces of travertine, a sedimentary, porous rock. These fragments once formed part of a large sculpture by British artist Henry Moore, called Arch. But over the years cracks began to show, and in 1996 the sculpture was dismantled.

Now, 12 years later, engineers and art conservationists have joined forces in an attempt to put the sculpture together again — assuming they can find the money.

Moore’s giant arch, constructed in 1980, was based on the shape of sheep collar-bones. It stood more than six metres tall, and was some 3.5 metres wide. It was constructed from seven separate pieces, each weighing around seven tonnes and held together with epoxy resin.

The rock pieces were manufactured according to a prototype constructed by Moore. The fact that this was made from polystyrene blocks might have had something to do with the sculpture's demise.

Rock resurrection

If Arch is ever to stand tall again, it needs to be put back together so that it stays in one piece this time. That is where rock engineer John Harrison from nearby Imperial College London steps in. “I know how rock behaves in an engineering sense; sculptors don’t,” he says.

Harrison has created a three-dimensional model of the arch, to see where the major stresses were. This should help engineers work out why the original cracked so badly.

The laser reconstruction shows the sites of the sculpture's main strains. Credit: Imperial College

Harrison used data collected by Angela Geary from the Glasgow School of Art, UK. Geary scanned the fragments using a technique called phase-shift laser scanning. Rather than the standard laser scanning technique, in which reflected laser light is measured close to an object, this technique measures the change in phase of the laser light, which means that a wide area can be scanned from afar, allowing the massive structure to be scanned more quickly.

Laser scanning is used in museums already, although not widely, says Martin Cooper of the National Conservation Centre at National Museums Liverpool, UK. This non-destructive technique is mainly used to create replicas of delicate artefacts, he says. “A lot of objects are too fragile to put a mould on.”

Geary collected swaths of data: “On average, 40,000 points per square metre were captured from Arch,” she says. Harrison thinned out the data, then used a technique called finite-element analysis to reduce the resulting structure to a set of simple three-dimensional shapes such as tetrahedra, triangular prisms and cuboids.

That was no mean feat, says Harrison. “This is a very complicated object,” he says. Geary adds: “We had to trade off between enough accuracy to give meaningful results, but not so much that it would be impossible to compute."

Shaky ground

“From my point of view [Moore] made it completely wrong. John Harrison , Imperial College”

The reconstruction has allowed the team to see exactly where the stresses formed in the sculpture, and why. Harrison says that the likely cause of the cracks was the fact that Arch was built on soft ground, and each foot could move independently.

This wasn’t the only problem: “From my point of view [Moore] made it completely wrong. He used the wrong material and put the joints in the wrong places,” says Harrison. Travertine is a weak porous rock, he adds, and this makes its density inconsistent throughout any one block.

To put the sculpture back together will need the cooperation of the Henry Moore Foundation, a charity set up by the sculptor himself in 1977 before his death in 1986. The foundation is in the process of deciding if it can fund the rebuilding, estimated to cost tens of thousands of pounds.

Harrison recommends building a new support, which can be hidden underground, and that the seven pieces be put back together with dowels and bolts, once he has analysed the slightly different stresses on the structure that will occur with these in place. Unlike solving a typical engineering problem, he will need to make sure that these are well hidden, and that any work can be reversed if necessary.

When damaged sculptures are rebuilt, the pieces are usually just put back together, without taking into account this type of stress on the structure, says Cooper. “Normally it’s like a huge three-dimensional jigsaw puzzle,” he says.

Harrison hopes one day to see the sculpture back in Kensington Gardens, where Moore had intended it to stand. But he remains certain that Moore’s engineering skills were not good. “Had I produced it, it wouldn’t have looked anything like this,” he says.

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Sanderson, K. Engineers come to art's rescue. Nature (2008).

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