For dozens of years there was an empty frame on a wall along the Papenstraat in Zwolle. Then, on request of the owner of the building, the inside of the frame was examined and old text was discovered underneath several layers of paint. After 150 hours of carefully scraping away paint, 5 different historical wall advertisements were found dating from the period 1890-1955: from a shoemaker, two from a bicycle dealer, and two from a furniture maker.
Two sheets of paper underneath the frame explain what can be seen here. Nice fact is that the cleaning project was named "Project Toverbal" ("The Gobstopper Project"), as -like the candy reveals different colours- each layer dissolves a different item.
For a few more photos from the project go to their website HERE.