The Elgin and Wintergarden Theatre in Toronto was left empty for 60 years. When they set about restoring it to its original beauty, they had to find a way to clean the walls, which were all painted with intricate murals, all in water based paint. How do you clean that without destroying it?
They use a museum technique. Make a bread dough like batter of ordinary flour and water. Then simply kneed the dough over the wall. It picks up the dirt without removing or wetting the paint.
The most difficult part was getting all the workers to work to exactly the same level of cleanness to have an even looking wall.
You may remember that last year we discovered that the same flour and water dough was the best material for removing the silicone film left after cutting off the caulking around the bathtub.