A British woman has helped uncover an Italian masterpiece, and by doing so ended a mystery over exactly who painted it.
The piece in question is the Ognissanti, or All Saints, Crucifix - which depicts Christ on a wooden cross nearly 5m (15ft) high.
On one side is the Virgin Mary, on the other, St John the Evangelist. It is thought to have been painted between 1310 and 1315.
Restorer Anna-Marie Hilling says removing years of grime has revealed incredible colours, convincing restorers that it is by Giotto.
For years, the crucifix had been left in a side room of a church in Florence, unseen, unadored.
There was always a suspicion it might be the work of Giotto di Bondone who, in the early part of the 14th Century, refashioned Italian art, helping give birth to the Renaissance.
'Revolution in art'
"What he did had never been done before," says Marco Ciatti, the head restorer.
"He was the first here to create a naturalistic human style of Christ on the cross, showing the pain, the man. Until Giotto, Christ was portrayed in a more stylised way. Giotto heralded a revolution in art."
In other words, Christian art, for the first time, spoke directly to its audiences, thanks to Giotto.
That was something they had never experienced before.
The trouble was, when it came to the Ognissanti Crucifix, there were always questions about who actually created it.
That is because centuries of candle smoke and poor attempts at maintenance had left the artwork covered in black dirt and unrecognisable.
Some experts believed it came from Giotto's workshop in Florence, but was not by the man himself.
Others thought it was the work of a pupil, or possibly a relative.
But then Florence's renowned restoration laboratory, the Opificio delle Pietre Dure (OPD), found sponsorship to restore it.
And now, after a mammoth seven-year project, the Ognissanti Crucifix has been brought back to life, with most experts now satisfied it is Giotto's work.
One of the key members of the team behind the clean-up has been Anna-Marie Hilling, originally from Cumbria in the north-west of England.
In 2004, she beat hundreds of applicants from all over the world for a coveted student place at the OPD.
The OPD only takes around six students every two years for its painting restoration course.
Her dissertation was on the Ognissanti Crucifix.
A year later she joined the restoration project permanently, making her one of the few to work on it continuously for the past seven years.
Ms Hilling says: "It has been a long, difficult job. I think the cleaning part was the most challenging, trying to get rid of the pollution before we could begin to actually restore it."
With such an irreplaceable work of art, it was an extremely delicate task.
Special solvents were used to lift the grime, but without destroying the paint underneath.
Much of the cleaning was done under a microscope.
"It was when we were doing the hands of St John the Evangelist, that we noticed the incredible colours coming through," says Ms Hilling.
"They were so vivid and this helped convince us it was a Giotto," she says.
You can now see the stunning results of the full restoration, Giotto's brushstrokes again on display.
A vivid example of the change can be seen on the face of the Virgin Mary.
The black has gone, replaced, instead, with her flesh colour.
More importantly, her tortured look of anguish is vibrantly clear to see.
Even the wrinkles around her eyes and mouth are now apparent.
It was not just the cleaning that convinced everyone this was a Giotto.
The giant structure was also X-rayed, enabling the original nails and construction to be seen.
It seems that Giotto was not happy with the original position of the arc over Christ's head, so he lowered it a few centimetres.
Together, the cleaning and the X-rays removed any lingering dirt and doubt about its true origin.
"It's a Giotto, and with this work he helped change the world," says Marco Ciatti, the chief restorer.
"Now the people of Florence will get a chance to see this masterpiece again."
The Ognissanti Crucifix has been returned to the Ognissanti Church, not far from Florence's famous bridge, the Ponte Vecchio.
"It's been an incredible experience, one that has enriched me both intellectually and emotionally", says Ms Hilling.
"To be allowed to get up close to such a wonderful classic has been a privilege, and now it's a joy to see it back where it belongs," she says.