High on the scaffolding in front of Michelangelo’s The Last Judgment, inches from the saints rising to Heaven and sinners sinking to Hell, it is the intense, staring eyes of the 300 painted figures that grab the attention — but something else is worryingly visible, too.

“Look at this whitish colouring,” says Paolo Violini, the Vatican’s chief painting restorer, pointing to a stain on the muscular arm of a man close to the central figure of Christ. “That’s the deposit left by years of evaporated sweat from thousands of visitors,” he explains. “And we need to clean it up.”

Restoration work on Michelangelo's Last Judgement, showing a muscular figure looking to the right with other figures behind and beside him.

A team of 30 are giving the the Sistine Chapel’s 16th century masterpiece a spring clean this month to restore its stunning palette, from the vivid blue sky thronged with angels to the shaded entrance to Hell. Barbara Jatta, the head of the Vatican museums, says: “People are going to be able to see Michelangelo’s magical, marvellous colours again.”

Barbara Jatta, Director of the Vatican Museums, speaks to reporters with microphones and cameras in front of Michelangelo's Last Judgement in the Sistine Chapel during maintenance.

Barbara Jatta

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Used by cardinals to elect new popes and taken over once a year by pontiffs to baptise babies, the chapel is otherwise crammed with daily visitors who gaze at Michelangelo’s depiction of Judgment Day above the altar then crane their necks to admire his ceiling fresco of God giving life to Adam.

The Sistine Chapel ceiling frescos, including "The Creation of Adam," and the "Last Judgement" are undergoing extraordinary cleaning maintenance, covered by a replica for protection.

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The visitors’ evaporating perspiration — levels of which officials say is increasing due to climate change — contains lactic acid, which combines with calcium carbonate in the wall of The Last Judgment to produce calcium lactate, a white salt which has built up as a patina across the fresco since it was last restored in 1994.

Luckily, getting rid of it is quick and cheap. Two highly absorbent sheets of Washi paper, made from plant fibre, are applied to the paintwork. Then a brush is used to apply demineralised water, which soaks through the paper and moistens the salt, causing it to adhere. “It’s simple — the salt comes off with the paper,” said Violini.

A scaffolding covered with a cloth depicting Michelangelo's Last Judgment in the Sistine Chapel.

A cloth depicting The Last Judgment covers scaffolding being used to work on the wall

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The cleaning of The Last Judgment, due to finish by Easter, has coincided with the annual dusting of the frescoes around the chapel, which is undertaken at night.

The Sunday Times was given a rare chance on Saturday to climb the scaffolding with members of the Vatican’s team of salt removers and see how Michelangelo’s true colours are re-emerging — starting with the gruesome figure of Minos, the judge of the underworld whose genitals are being bitten by the snake coiled around his body.

Illustration of "Group of the Damned" from Michelangelo's "The Last Judgment" fresco, depicting nude male figures with grotesque features, some with horns or snakes wrapped around them, signifying their damnation.

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A resentful Michelangelo gave Minos the face of a papal official who had complained about the amount of naked, muscly men included in the fresco, which were probably inspired by the artist’s visits to Rome’s public baths which doubled as brothels for male and female prostitutes.

Further up the scaffolding, viewers pass discreet cloths painted over genitalia after Michelangelo’s death.

Michelangelo's fresco painting "The Last Judgment" covering an entire altar wall.

As the artwork usually looks

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Giandomenico Spinola, a Vatican museum official, says he felt a renewed appreciation for Michelangelo’s genius: “How did he paint those perspectives so fast, so close to the plaster, which are perfect seen from distance? I can’t explain it.”

Next is St Bartholomew, who was flayed alive. He is holding a stretch of skin in his hand which features facial features, reputed to be a self portrait of the artist.

Fresco of Saint Bartholomew displaying his flayed skin.

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At the seventh and final level of the scaffolding, 20 metres up and level with the ceiling, Fabrizio Biferali, one of the museums’ curators, points to where the worst salt stains form distinctive white blotches.

“The Last Judgment has been affected by the salt more than other walls or the ceiling because this wall is colder than the others, hence more condensation,” he says.

There is another factor, he adds. Michelangelo insisted that the wall protruded by about a foot at the top, making it lean outwards, so viewers had a good view of the angels. An unforseen consequence was more rising vapour from sweaty tourists being captured by the wall.

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Back at ground level, Jatta says visitor numbers were reduced last year to help safeguard the paintwork.

A group of visitors taking a selfie inside the Sistine Chapel while "The Last Judgement" painting is undergoing maintenance.

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“Popes ask us to make this an open place, but we will control numbers and do not now let in more than 24,000 a day,” she says.

She has loved the opportunity to get so close to The Last Judgment, she admits: “You can see the light and shade on skin. It’s amazing — nothing else compares.”