The hunt for Leonardo da Vinci's greatest lost fresco is back on - but it'll take a while yet.
Experts said Thursday they would need some 18 months to establish whether the fabled fresco of the Battle of Anghiari is hiding behind a secret wall in Florence's Palazzo Vecchio, underneath a later painting by the famous art historian Giorgio Vasari.
The search for the fresco was greenlighted in January by Italian Culture Minister Francesco Rutelli.
It was led by art sleuth Maurizio Seracini, the only real-life character in Dan Brown's bestselling thriller The Da Vinci Code, and the man who uncovered the wall two years ago.
Now a panel of art experts will assess the findings, under the supervision of Florence's famed heritage restoration body Opificio dell Pietre Dure.
The committee met for the first time Friday, saying they had "a pile of diagnostic work" to do.
Seracini claims the wall hides "significant" traces of the fresco.
The panel will examine new evidence as well as poring through past studies and Florentine archives.
The discovery of the wall in summer 2005 raised new hopes of finding this Holy Grail of the art world.
But opinion was divided.
The world's top Leonardo scholar, Carlo Pedretti, was convinced the fresco could be hiding inside the palazzo's Salone dei Cincequento.
"I really believe it's behind that wall," said Pedretti, director of the Armand Hammer Center for Leonardo Studies at the University of California.
He said Renaissance accounts showed "the fresco can only be there".
Pedretti was also optimistic about finding the fresco virtually intact.
He rejected suggestions that Vasari, might have damaged the fresco when he was told to cover it.
Vasari was asked to paint over masterworks by Giotto and Masaccio in two other Florentine sites, but left the underlying works intact, Pedretti noted.
"If he didn't damage those ones, why should he have done so with the Leonardo?"
This optimism contrasted with the views of then Florence art chief Antonio Paolucci who said after the wall find was unveiled that "there's little or nothing behind that wall".
Paolucci, a former culture minister, may now have changed his mind - since he was one of the officials who decided to set up the international panel.
'ANGHIARI' KNOWN FROM COPIES, SKETCHES.
The Battle of Anghiari - described by sculptor Benvenuto Cellini as a ground-breaking masterpiece that any artist simply had to see and study - has long been known from sketches and copies.
But the original was thought lost for ever - a victim of Leonardo's typically unorthodox decision to jettison the traditional technique of applying paint to wet plaster.
Leonardo needed time for his painstaking approach and so used oils directly on the dry plaster in Palazzo Vecchio, the symbol of Florentine civic pride.
Like the Last Supper in Milan it soon began to crumble, helped on its way by a thunderstorm that hit the unfinished building.
Leonardo gave up and headed for Milan.
Though it has been wiped off the art map, the fresco's birth was well documented.
Leonardo (1452-1519) started painting it on June 6, 1505, surrounded by an admiring throng.
Soon after, on a facing wall, Michelangelo started another great martial fresco destined to remain unfinished, the Battle of Cascina.
