Depending how rusted and corroded your key may be, you can try a few things to clean it up: 1. Fill the bottom of a saucepan with distilled white vinegar, drop in your keys and heat on low on your stovetop. You can see this vinegar cleaning process in action on YouTube. 2. If they are just heavily tarnished (and not rusted) you can use the method I showed you recently in my How To Clean Silverware With Baking Soda And Aluminum Foil article. 3. You can also rub the keys with ketchup, let sit for 5 minutes, rinse and buff them with a clean cloth. If none of those methods work well enough for you, you can always spray a light coat of bronze spray paint on the key to brighten it up. My key was a combination of tarnish, rust and years of wear and tear, so I opted for the light coat of spray paint.