Italian master artist Giotto (Giotto di Bondone born 1266 and died 1337) is particularly famous for two series of frescos in honor of John the Baptist and St. John the Evangelist in Peruzzi Chapel in Florence's Santa Croce church. The frescoes were completed in 1320. The most famous scenes include an image of St John the Evangelist ascending to heaven, and a Roman soldier presenting the severed head of St John the Baptist on a plate to King Herod. Recently, restorers mapping and measuring the frescos for future restoration discovered that under ultraviolet light, no longer visible colors and details could be seen once again. In the image of St. John the Evangelist below, the version on the left is photographed under normal light; the image on the right is taken under ultraviolet light.

It's generally believed that these frescoes, created at the tail end of Italy's medieval era, and the cusp of the Renaissance, influenced Michaelangelo two hundred years later. Already, you can glimpse Giotto figuring out true perspective. In the eighteenth century the frescoes were covered with a lime-based white-wash, and then, crudely restored in 1840 with caustic cleaners, solvents, and steel wool brushes which damaged the paintings.

Cecilia Frosinini, mural paintings section director at Florence's Opificio delle Pietre Dure art restoration laboratory, worked in collaboration with the Getty Institute in Santa Monica to restore the images. While long-term exposure to ultraviolet light would further damage the frescoes, the plan is to photograph and then render a detailed digital version of the paintings in all their glory. You can read more about the discovery here. The video below shows the difference the ultraviolet makes, as Frosinini explains the process.