PRATO, Italy — This Tuscan city was once the scene of one of the most romantic scandals of the Italian Renaissance. Here, the artist and Carmelite monk Fra Filippo Lippi was commissioned to paint an altarpiece for the convent of Santa Margherita, and happened to meet there an attractive young novice, Lucrezia Buti. The couple had an affair, and in around 1457 produced a child, Filippino Lippi, who was to become a celebrated painter in his own right.