Check out this fascinating article about restoration and new discoveries concerning the Giotto Frescoes in the Peruzzi Chapel:
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 subject line is taken from The Prime of Miss Jean Brodie, by Muriel Spark. Giotto is not my favorite, though I do love him. Fra Angelico is my favorite.)