A few years ago in Manhattan, I seen a building being demolished. It was next to another building that had been built before the building that was being demolished was built. One of the abutting walls had a huge advertising mural , back from the same time period as your find when they actually painted them. It was of a laundry detergent and had a lady hand washing clothes in a tub with the wavy metal plate with the two rollers on it. Was pretty cool to think that had not seen the light of day in well over 120 somthing years and was preserved between the brick walls.