Seen in a new light, Giotto's Florentine masterpieces

Restoration experts have used ultra violet rays to shine an astonishing new light on the work of one of the most important painters in the history of Western art.

The paintings of Giotto di Bondone in the Peruzzi Chapel in Florence's Santa Croce church are considered among the most important by the medieval artist who introduced a revolutionary emotional depth and degree of perspective in his painting.

The Peruzzi chapel, with its murals honouring John the Evangelist and John the Baptist, is thought to have inspired great painters in the Renaissance a century after Giotto's death in 1337. But neglected for hundreds of years, and encrusted with dust and crime, it is only now that some of the finest details have been seen again.

The ambitious "non-invasive diagnostics" project designed to assess the condition of the 12-metre-high chapel, which Giotto painted in about 1320, began last year. By chance restorers working on the three-storey steel scaffolding noted that when ultra-violet light was directed on the frescoes a remarkable degree of extra detail became visible.

Cecilia Frosinini, who co-ordinated project, told Corriere della Sera that when the UV light went on, "all that was opaque, uncertain and illegible became clear, dense and full of contrast".

"We have uncovered a secret Giotto," said another of the team, Isabella Lapi Ballerini, head of Florence's Opificio delle Pietre Dure art restoration laboratory.

The aim of the study, which involved more than a dozen experts and was partly funded by the Getty Foundation in Los Angeles, was to gather information on the 170-square-metre chapel to use as a plan and "hospital chart" for a future restoration.

The chapel had been restored in 1958, with the focus on removing the "non-Giotto" elements added by 19th century artists. Despite the painstaking work, the art was still regarded as a pale shadow of its former self. But the current restoration team says that under UV light a remarkable transformation occurs – and hints at what a more fully realised restoration might achieve in the future.

In a scene in one of the frescoes in which God is seen accepting John the Evangelist into heaven, fine details of facial expression are illuminated.

Art experts speculated yesterday that the discovery that UV could reveal so much about the original version of the paintings might have important implications for other works by the artist. The influence of Giotto, who is often referred to as the "Father of Western painting", is said to be visible in the work of the great figures of the high Renaissance such as Michelangelo.

Ms Frosinini told Reuters of her surprise and delight when she saw the "images come back to life". "I just hope we can find enough funds to have a complete ultra-violet mapping of the whole chapel in order to build some kind of virtual software to share all that we have discovered with the public," she said. The use of ultra violet light has to be limited because it too, might damage the paintings, which are particularly fragile because they were painted on dry plaster, unlike traditional frescoes.