'World's most beautiful drawing' out of vaults for two-hour outing

A sketch executed by Leonardo da Vinci for his masterpiece The Virgin of the Rocks, one version of which hangs in the National Gallery in London, gets a rare outing today when, for an afternoon, it will be removed from the hi-tech glass case in which it is preserved in the vaults of Turin's Royal Library, along with other treasures of the Renaissance.

For two hours, the exquisite drawing of the angel, described by the Italian art connoisseur Bernard Berenson as the most beautiful drawing in the world, will hang in the library of the Piazza Costello in Turin, in a sumptuous interior designed by the 18th-century Bolognese artist Pelagio Pelagi, to be admired by small guided groups.

Tomorrow it will be replaced in a glass case that protects it from the atmosphere and returned to the vault, where it becomes a centrepiece of a new show featuring works by Antonello and Jan Van Eyck as well as Leonardo.

The sketch was part of preparation for an altarpiece intended for a chapel in the church of San Francesco in Milan. The version of the painting in the National Gallery is one of the Leonardo works to be examined for the artist's fingerprints in the Universal Leonardo Project, set up to co-ordinate the first scientific examination of all his paintings.

Sister Wendy Beckett, in her book The Story of Painting, writes of the painted angel that it has "an interior wisdom, an artistic wisdom that has no pictorial rival".