<P> For this work, Leonardo sought a greater detail and luminosity than could be achieved with traditional fresco . He painted The Last Supper on a dry wall rather than on wet plaster, so it is not a true fresco . Because a fresco cannot be modified as the artist works, Leonardo instead chose to seal the stone wall with a double layer of dried plaster . 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 had recommended the use of secco for the final touches alone . These techniques were important for Leonardo's desire to work slowly on the painting, giving him sufficient time to develop the gradual shading or chiaroscuro that was essential in his style . </P> <Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (May 2012) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (May 2012) (Learn how and when to remove this template message) </Td> </Tr> <P> Because the painting was on a thin exterior wall, the effects of humidity were felt more keenly, and the paint failed to properly adhere to the wall . Because of the method used, soon after the painting was completed on February 9, 1498 it began to deteriorate . As early as 1517, the painting was starting to flake, and in 1532 Gerolamo Cardano described it as "blurred and colorless compared with what I remember of it when I saw it as a boy". By 1556--fewer than sixty years after it was finished--Leonardo's biographer Giorgio Vasari described the painting as already "ruined" and so deteriorated that the figures were unrecognizable . By the second half of the sixteenth century Gian Paolo Lomazzo stated that "the painting is all ruined". In 1652, a doorway was cut through the (then unrecognisable) painting, and later bricked up; this can still be seen as the irregular arch shaped structure near the center base of the painting . It is believed, through early copies, that Jesus' feet were in a position symbolizing the forthcoming crucifixion . In 1768, a curtain was hung over the painting for the purpose of protection; it instead trapped moisture on the surface, and whenever the curtain was pulled back, it scratched the flaking paint . </P>

Leonardo da vinci's picture of the last supper