Restoration and conservation of works of art is far from an exact science. Last year controversy erupted over plans to restore Michelangelo's sculpture group, Victory, in Florence's Palazzo Vecchio, and over a delay for a scientific conference on the stabilisation of the leaning tower of Pisa.
Opinions inevitably differ widely on the techniques and procedures for preserving the unique and priceless and safeguarding them for future generations.
"There are very strong powers in play that discourage any criticism, that dissuade anyone from rocking the boat," said James Beck, head of ArtWatch International and professor of art history at Columbia University, United States, for more than 30 years.
He founded ArtWatch in 1992, and it now has about 600 associated art historians, artists, restorers and interested members of the public who keep a vigilant eye across the world.
ArtWatch's mission is to blow the whistle on mistakes in restoration and conservation, or on any suspected errors in the art world. In the mid-1990s, Michael Daley of ArtWatch UK challenged the authenticity of a painting attributed to Rubens that the National Gallery had bought for Pounds 2.5 million. The case is still open.
"It is not so much an issue of right or wrong," said Professor Beck. "But of the need for total freedom of information and open discussion. In this sense many of my colleagues are guilty. One thing that happens is that if an academic speaks out against what he considers a mistake in restoration, conservation or attribution, he is denied access."
In 1992, Professor Beck was sued for criminal libel by the restorer of the famous Ilaria del Carretto, a 15th-century statue in the Cathedral of Lucca. "It had been cleaned so disastrously that I spoke out," said Professor Beck, who won the case.
Over the past few years he has haunted the nightmares of many Italian restorers and local politicians, perhaps inevitably in the light of the country's concentration of treasures. "I am not anti-Italian but I do feel a responsibility to speak out when I know that what I'm saying is right," he said.
HERITAGE AT RISK: ARTWATCH'S ITALIAN CAMPAIGNS Stalling by scientific authorities has allowed damage to the leaning tower of Pisa to continue unchecked, according to Ar****ch, which last year expressed concern at the narrow circle of consultation and disappointment at the delay in assembling an international expert group until April 1999
Plan to restore Masaccio's Trinity, in Santa Maria Novella, in Florence, abandoned in 1994 after Ar****ch began a legal action
Ar****ch last year called on the mayor of Florence to halt restoration of Michelangelo's Victory to allow the intended methods to be assessed
Restorers of the Sistine Chapel accused of over-cleaning Michelangelo's frescoes, scraping off a final layer of subtle shading that Michaelangelo had applied
Scrovengni Chapel in Padua, which houses a series of frescoes by Giotto, was endangered by a concrete and steel structure, newly built onto the side of the chapel and which, in the event of earth Tremors, could hammer the original stone chapel to pieces. Professor Beck and an Italian art historian, who shared his opinion, where refused permission to speak at an "open" conference on the restoration of the frescoes
Before the 1997 earthquakes in Assisi, Ar****ch warned that a rotten wooden beam in the roof of the Cathedral of Saint Francis should not have been replaced with a pre-stressed concrete beam which would not absorb vibrations. Part of the cathedral's ceiling collapsed in the earthquake, killing three people. It is not certain that the beam was responsible, but art historian Federico Zeri agrees that it was.