The Cathedral of Learning is such a beautiful building. I wonder though: did they leave any dirty patches as a small reminder? When they cleaned the ceiling of

The Cathedral of Learning is such a beautiful building. I wonder though: did they leave any dirty patches as a small reminder? When they cleaned the ceiling of the great hall of Grand Central Terminal of the tobacco stains and train soot, a small patch was left dirty to show how filthy it was before the restoration [1]. As a kid, seeing that patch was a powerful argument to never smoke tobacco. 1. http://www.atlasobscura.com/places/grand-central-ceiling-dark-patch http://www.atlasobscura.com/places/grand-central-ceiling-dar...