 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.