Chalk or the pounce which uses chalk; you can spray it lightly with hairspray to make it last longer. I've used a sliver of soap and that worked good as well. If you use the blue pen make sure you don't get heat on it because it'll set in in and then you have to soak it to keep it from coming back. If you just run water over it it'll disapear but will come back later. I always soak mine for a while to prevent it form coming back.