I use all the leftover ketchup packages from restaurants as wonderful copper and brass polish. Ketchup is a non-toxic way children can polish copper for Montessori practical life skills. The packages don’t dry up and are ready to use. Make a tray with the ketchup packages in a small basket, a damp piece of sponge for cleaning, a copper ornament and a duster for polishing the cleaned object. I find that you need to wash the ketchup off the cleaned piece with soapy, warm water and then rinse well.