Here's a secret I found when using tempera paint on things other than paper. When we make turkeys or rabbits from milk cartons, I found that tempera paint often flakes off the waxy milk cartons after they've been painted. Now I mix white glue in the paint so that about 1/8 of the paint is glue. When the paint dries, it does not flake off. This method also helps paint stick to glass bottles, jars or plastic containers.