What is the outline of the history of Leonardo da Vinci's The Last Supper indicating the problems that almost destroyed the masterpiece and efforts...

Leonardo da Vinci painted The Last Supper during the years
1495-1498. He did not follow the true format for painting a fresco, which requires that
pigments are applied to a newly plastered and still wet wall. This procedure allows the
pigment to bond with the plaster as it dries but does not permit changes in the work as
it progresses. Leonardo chose to paint on dry plaster, which allowed him to make changes
but also left the work much more vulnerable to changes in y
humidity.

The paint started flaking in the early 1500s and
was described as "unrecognizable" by 1556. In 1726, the first unsuccessful attempt at
restoration involved using oil paint over missing sections and varnishing the entire
work. In 1821, an attempt was made to remove the painting for repairs, based on the
impression that it was a true fresco. Part of the mural was badly damaged before the
effort was halted. The mural was again studied and cleaned 1901-1908. Using modern
photographic techniques, The Last Supper was again extensively researched beginning in
1978. Based on information gained, the painting was cleaned, restored, and repainted
where necessary. It was reopened for limited public viewing in a climate-controlled
environment in 1999.