Restoring The Last Supper of Leonardo da Vinci - 20 years journey

Leonardo Da Vinci painted "The Last Supper" between 1495 and 1498, with measurements of 460 cm × 880 cm (180 in × 350 in).
The work was commissioned by Leonardo's patron Ludovico Sforza, Duke of Milan, as part of a plan of renovations to the church and its monastery buildings.
While Renaissance masters painted traditional frescoes on wet plaster wall, da Vinci experimented this painting with tempura paint on a dry, sealed plaster wall in the Santa Maria delle Grazie convent in Milan, Italy. However, the experiment was not successful due to technical problems. The paint did not adhere properly and began to flake away just a few decades after the work was completed.
At the end of the 20th century, Italian restorer Panin Brambilla Barcilon and her team started restoring the original as accurately as possible.
The task of restoring was huge, including removing five layers of paint from previous botched restorations and restoring key features and objects. Panin Brambilla and her colleagues took more than 20 years to complete the thorough job of cleaning, dabbing, and repainting.
The restoration was finished in the spring of 1999 and cost millions of dollars.
This video shows Pinin Brambilla's story about the restoration in an interview with Witness.