Brambilla is slightly schoolmarmish. She is elegantly dressed, has her hair up in a grey bun and wears gold-rimmed glasses over fine features. She has the skin of a person who avoids the sun. She is a picture of severity. "We lost a whole week's work facilitating the TV crew and then they come out with this cheap criticism," she snorts. "There is always room for polemic but it must be loyal and not gratuitous."
She is equally contemptuous of other critics, especially Professor James Beck of Columbia University, who has been relentless in his condemnation of her efforts. Beck argues that she has not restored Leonardo but produced "a new Brambilla", something that resembles a postcard. "It has no more in common with the original than previous over-paintings, which at least were guided by Leonardo's work."
He is not alone in his view. "Ninety per cent of the work has disappeared," laments Jacques Franck, a restorer at the Louvre and da Vinci scholar, "and they have turned it into a 20th-century Leonardo."
Consider, too, the words of Carlo Pedretti, Italy's foremost Leonardo expert. "I have some perplexities about the overall philosophy of intervention. We have lost a repainting that started a century after Leonardo's death and was part of the historical context of the work," he says. "Pinin Brambilla has destroyed the historical thread of the painting," concludes Michael Daley of ArtWatch UK. Even the world's most famous art historian, Ernest Gombrich, is reported to have obliquely criticised the restoration with a Latin phrase, Quieta non movere, which could be roughly translated as let sleeping dogs lie.
"These are all last-minute criticisms," says Brambilla dismissively, as we dodge wires and workmen fine-tuning a new air-conditioning system. We are in the friary of Santa Maria delle Grazie in Milan, the very place in which Leonardo was first commissioned to paint the Last Supper by a member of the Sforza family at the end of the 15th century. "We've been working on this for 20 years and art professionals have had ample opportunity to inspect the work. Those who did have been impressed."
Brambilla became involved with The Last Supper in 1977 while restoring another painting at Santa Maria. Until that time, debate had centred on the preservation rather than the restoration of the painting. The arrival of a new director at Italy's Central Restoration Institute marked a change of direction. Suddenly the philosophical emphasis changed. Science and technology were to be placed at the service of art, replacing the age- old concept of the restorer as pure artisan.
Science and technology had much to reveal. Extensive analysis confirmed the experts' worst fears. What little remained of Leonardo's original 1498 brushwork was in fact being eaten away by the layers of paint - and worse - that had been applied to the painting by subsequent generations of well-meaning restorers. It was decided that to stop further deterioration the later additions must be lifted.
Yet, ironically enough, the first person to bear responsibility for the pitiful decay of the work was the artist himself. Leonardo's obsession with experimentation led him to try out an entirely new technique, that of applying tempera and oil to a dry wall. Traditional fresco technique - in which the artist paints directly on to wet plaster - didn't suit him, as it didn't permit revision once the plaster dried. The 9x4- metre Last Supper is a huge painting and the artist wanted to be able to make adjustments to colours and forms as he went along. But in trying his new technique, Leonardo failed to take into account two factors: the stability of the wall and the humidity of the environment. Sure enough, within his own lifetime, The Last Supper had already buckled, cracked and begun to peel.
So The Last Supper has been in a state of "restoration" almost from first conception. Subsequent to Leonardo's own efforts, it's been re-painted, varnished, glued, stuccoed, waxed and even ironed, to sometimes catastrophic effect. Brambilla is grim as we enter the refectory. "Some of the worst culprits were the 17th- and 18th-century artists who repainted it according to the tastes of their era," she says. "If you think that John Ruskin compared this work to Rembrandt, you realise how much the restorers had distorted the colours."
The big moment has come. The long, white-walled, gracefully vaulted refectory is completely empty. The workmen nearby have suspended their drilling. As we move forward, our shoes tip-tapping on the tiled floor, I hesitate. Maybe, after all the build-up, this close encounter with one of the cornerstones of Western art might be an anticlimax. I lift up my eyes, as they say, and there it is high up on the end wall, free of scaffolding at last.
What first strikes you is the light, the sheer luminosity of it. The colours are clearer and more vibrant and there's huge variety of tone. To my untutored eye, it finally looks like an Italian Renaissance painting, more Piero della Francesca than Rembrandt. It's certainly no longer that gloomy, grimy, ill-defined enigma that I toiled over in sixth-form Art History. It still looks scaly on the surface but now you can actually see the faces and figures within the image, and what they're doing and seeming to say. The picture has a story to it. It is more accessible.
It makes me smile rather stupidly.
Pinin Brambilla interrupts my meditation. "The scientist in Leonardo used the light that comes in through the painted windows to illuminate the table, and let it reflect off the metal plates, which in turn reflect the colours of the apostles' robes," she says. As I am reminded of her presence, I wonder just how much of the Dottoressa there is in this "new version". The image appears deeper, not so two-dimensional and you see how Leonardo perhaps wanted the painted space to appear as an extension of the dining hall in which the friars would congregate to eat. The landscape in the painted windows behind the table was once a blur. Now a belltower is visible, and experts note that the hills are more northern Italian than Tuscan. Flowers, bread, plates and chalices have emerged out of the murky mass that was once the table.
For Brambilla, one of the most fascinating aspects of her labours was revealing the original faces. "The features had been completely altered [from the original]. Figures that Leonardo had painted in three quarters had been changed so they were in profile and the actual profiles have been distorted. Noses and beards were enlarged, mouths that were opened were closed."
Stepping back I feel a slight, almost imperceptible breeze. To ensure the newly revealed elements won't suffer damage from 20th-century pollution, a state-of-the-art air-conditioning system has been installed. I have just crossed one of the "air walls" that divide the chamber. These are supposed to ease away from the work any particles of smog, dust and dandruff. The environment resembles that of an operating theatre. Temperature and humidity are kept constant and special mats have been installed to absorb the particles that escape the air walls. There will be a limit of 100 visitors per hour and there are already bookings well into summer.
No one can dispute that what those visitors will see is clearer and therefore more accessible. The big question is, how true to Leonardo is the restored work? Critics have suggested that as little as 20 per cent of the original remains and that by removing the work of previous restorers the painting has been deprived of its own history.
The most contentious issue is the decision to fill in with watercolours the so-called "dead areas" between the fragments of the original colours. According to the project's co-director, Dottore Pietro Marani, "it was an honest aesthetic decision to ensure unity". Presenting the pounds 6m restoration, Culture Minister Giovanna Melandri asserted that "no one can say it's not Leonardo". And on the controversy rages.
One thing seems likely, however. And that is that whether The Last Supper "is Leonardo" or not may, in the end, prove to be a side issue. After all, we find ways to be comfortable with what we are used to. The furore of a few years ago that accompanied the Japanese-financed clean-up of Michelangelo's Sistine Chapel has largely abated and the operation is now widely considered to have been a great success. The restored frescos, Last Judgment and all, are seen to work as art; it seems to matter less, now, whether they work as artistic archive.
As Dottoressa Brambilla shows me out into the busy 20th-century streets of Milan, a sign on Santa Maria's heavy gates flutters in the breeze and almost detaches. It reminds me of something I'd learned earlier in my visit: that no restoration is ever definitive and that the watercolours Brambilla used to fill in the gaps in da Vinci's masterpiece are reversible. She leaves me without a smile. She knows that, however the story ends, something is certain: no one will ever see The Last Supper in the same way again.