A Painting That Is Dying

The Last Supper began deteriorating during Leonardo's lifetime because he painted on dry plaster using an experimental oil-tempera technique instead of traditional fresco. Within decades, paint began flaking from the wall. By 1556, one observer called it a "muddle of blots."

Today's version is the result of a twenty-one-year restoration completed in 1999, which stripped away centuries of overpainting to reveal what remained of Leonardo's original surface — estimated at less than twenty percent of the visible paint.