Instructions
Place 1 tsp. salt in a small container. You'll want to use more if you plan on cleaning a lot of copper coins.
Mix vinegar into the salt. Add enough to soak all of the salt.
Apply this mixture as a paste to scrub the copper coins. You can clean them with your fingers or a tooth or nail brush.
Soak badly stained copper coins overnight in the salt and vinegar solution. Check the coins every couple of hours to determine if they are ready.
Use a brass brush on copper coins you don't want to soak or scrub. Rub it gently in a circular motion.
Wet your copper coins and rub baking soda into them with a toothbrush. This is a good method to use when you're afraid of scratching the coins with a regular brush.