As the wall was built of stone containing nitre, readily absorbing dampness, and as he was zealous fo producing splendid effects in coloring, the painter experimented in tempera, a medium still lacking in durability at that time. The painting had already suffered deterioration when Vasari in 1566 called it a “tarnished patch of colors.” Then there were external forces at work. The monks themselves committed vandalism by cutting a door through the wall just below the figure of Christ. When in 1796 the Napoleonic invasion entered Milan, the French soldiers used the refectory as a stable for their horses, although Napoleon had given orders that the picture should not be injured. Unfortunately, the general in command did not obey the instructions explicitly, for the French soldiers occasionally amused themselves by pelting the heads of the Apostles with clods of clay. In 1800, a flood covered the floor of the refectory to a depth of two feet, and when the waters subsided, the painting was covered with a thick mould. The picture has also