worked on The Last Supper from about 1495 to 1498, but did not work continuously. The beginning date is not certain, as the archives of the convent for the period have been destroyed. A document dated 1497 indicates that the painting was nearly completed at that date. One story goes that a prior from the monastery complained to Leonardo about its delay, enraging him. He wrote to the head of the monastery, explaining he had been struggling to find the perfect villainous face for Judas, and that if he could not find a face corresponding with what he had in mind, he would use the features of the prior who had complained. In 1557, Gian Paolo Lomazzo wrote that Leonardo's friend Bernardo Zenale advised him to leave Christ's face unfinished, arguing that "it would be impossible to imagine faces lovelier or gentler than those of James the Greater or James the Less." Leonardo apparently took the advice. Medium Leonardo, as a painter, favoured oil painting, a medium which allows the artist to work slowly and make changes with ease. Fresco painting does not facilitate either of these objectives. Leonardo also sought a greater luminosity and intensity of light and shade (chiaroscuro) than could be achieved with fresco. Instead of painting with water-soluble paints onto wet plaster, laid freshly each day in sections, Leonardo painted The Last Supper on a wall sealed with a double layer of gesso, pitch, and mastic. Then, borrowing from panel painting, he added an undercoat of white lead to enhance the brightness of the oil and tempera that was applied on top. This was a method that had been described previously by Cennino Cennini in the 14th century. However, Cennini described the technique as being more risky than fresco painting, and recommended the use of "a secco" painting (on dry plaster) for the final touches alone. Subject The Last Supper portrays the reaction given by each apostle when Jesus said one of them would betray him. All twelve apostles have different reactions to the news, with various degrees of anger and shock. The apostles were identified by their names, using an unsigned, mid-sixteenth-century fresco copy of Leonardo's Cenacolo. Before this, only Judas, Peter, John and Jesus had been positively identified. From left to right, according to the apostles' heads: Bartholomew, James, son of Alphaeus, and Andrew form a group of three; all are surprised. Judas Iscariot,