FLORENCE Italy (Reuters) - If there is any mind an art restorer would die to get into, it would be that of Leonardo da Vinci, the master painter, architect, engineer and inventor whose genius epitomized the brilliance of the Renaissance.
That was the unique opportunity restorers in Florence have relished as they clean the "Adoration of the Magi", a massive painting that Leonardo started in 1481 at the age of 29 but abandoned a year later, leaving it in various stages of conception and development.
The painting on wood, measuring about 2.5 by 2.5 meters (8.2 by 8.2 feet) depicts the three wise men who paid tribute to the infant Jesus in Bethlehem, but it also includes a riot of human figures, battling horses, architectural designs, landscapes and skies.
Done on 10 slabs of wood glued together, it has blank areas, areas with under-drawings, and sections in advanced stages.
"This is perhaps the most quintessential work-in-progress in the history of art," said Cecilia Frosinini, one of the directors of the ongoing restoration of the work, which is slated to return to Florence's Uffizi Gallery next year.
"Leonardo never wanted this to be seen by anyone at this stage, probably not even by those who commissioned it, probably not even his assistants. This is the phase in which he was still elaborating in his mind what the final work would look like," she said, standing in front of the piece.
Leonardo received the commission to paint an altar piece depicting the Adoration from the monks of the monastery of San Donato a Scopeto, near Florence. He stopped abruptly when he left to take up an offer of steady income from the Dukes of Milan.
In the late 1500s it was acquired by Florence's Medici family, whose restorers added layers of both clear and sepia-colored varnish to give it a homogenous, monochrome look when they put it in their collection.
The current restoration project, which began three years ago, has removed much of the dull, oxidized varnish as well as traces of past restoration attempts, revealing many previously hidden details, facial expressions and subtleties of light and shadow.
There are sections where the same horse's head is drawn in various positions, where horses in battle still have three hind legs because Leonardo still had not decided which would go and which would stay.
"The great fascination of this project was seeing something that we were not supposed to see, standing behind the artist and imagining what the final version could have looked like," said Patrizia Riitano, one of the two restorers who cleaned it.
"I hope that I have been able to enter Leonardo's mind, at least a little bit," said Riitano, who has also worked on paintings by Raphael and other Renaissance masters.
The restoration showed that despite the large size of his work, Leonardo did all the under drawings freehand, eschewing the "cartoons", or dotted-lined outlines, used at the time to divide large complex works into sections.
"We have gotten close to this inexhaustible genius who is never satisfied with his work, who wants to be totally free, even from himself, free from the restrictions that the cartoons would have imposed," said Frosinini.
"It is as if we are privy to a private conversation - Leonardo talking to himself, perhaps even arguing with himself," she said.
Experts at the Opificio delle Pietre Dure, Italy's premier, state-run art restoration lab, have ruled out a hypothesis put forward 15 years ago that Leonardo had done only the preliminary work and the paint was added by an unknown artist long after the master's death in 1519.
"Of course there were restorations and small additions here and there over the centuries but we are convinced that this is all substantially Leonardo," said Roberto Bellucci, a renowned expert on cleaning oil paintings who restored it with Riitano.
In 2001, the Uffizi, after much public and in-house hand wringing, decided not to restore the masterpiece because it was deemed too delicate by some.
Improved techniques and more scientific studies convinced the Uffizi to go ahead with the restoration this time.
Marco Ciatti, the head of the restoration lab, said that if the cleaning had not gone ahead, viewing it would have been "like trying to read a book of poems in a dark room".
After the wood backing of the painting is restored, it is due to return to a special room in the Uffizi, where it will be on display with two other Leonardo works.
Reporting By Philip Pullella; Editing by Michael Roddy and Sonya Hepinstall