Oops! There Goes Another Warhol - the Art That Can't Be Moved

Pablo Picasso's masterpiece depicting the bombing of the Basque village of Guernica during the Spanish civil war is now too fragile to move, according to curators at Madrid's modern art museum. Using x-rays and infra-red technology, 30 technicians have identified 129 changes to the huge painting. Much of the damage is thought to have occurred when it was rolled up for journeys around the world - having been shown in London, Paris, Milan, Munich, Hamburg, Cologne, Brussels, Amsterdam and Stockholm, as well as Sao Paulo and New York, its home for many years during the Franco dictatorship.

Guernica's globetrotting was mostly done in the 1950s but famous art does more air miles than ever these days. Stories of accidental damage include an Andy Warhol self-portrait ripped by a gust of wind as it was hauled from gallery to removal van, a Howard Hodgkin broken in half by a collapsing storeroom cupboard and a Rembrandt etching posted in a glazed frame with only bubble wrap and a padded envelope for protection.

Even respected galleries can damage work. Two American pieces fell from their hangings and broke during an exhibition of modern art from Los Angeles at the Pompidou Center in Paris two years ago. One had survived several earthquakes during its time in LA and the Pompidou was criticized by US artists and galleries for its apparent carelessness.

A spokesman for the National Gallery says it won't automatically refuse requests from other galleries to show its most precious works but its conservation team and curators assess each inquiry. Two years ago, The Ambassadors, one of the National's most famous works by Holbein, could not be sent one-and-a-half miles to Tate Britain for a major Holbein exhibition, because its wooden panels were judged too delicate to move.

Galleries will sometimes go to great lengths not to disturb fragile works. A huge canvas by Luca Giordano has been kept at the Herbert in Coventry during the art gallery and museum's £20m refurbishment. The picture was boarded up on site, but inspected every day to ensure it was not damaged by fluctuating temperatures and vibrations from the builders. It seems to have worked: it will reappear in the new old masters gallery next month.