A wonderful tip...

Brass can have a beautiful finish, but over time it acquires black stains. Some brass finishes are just a coating and not really brass. If you'd like to restore such a surface, first you have to determine whether the metal is ferrous (iron or steel) or brass. Test it with a magnet. A magnet will stick to iron or steel but not to copper or brass. If it looks like brass but the magnet sticks, it might have been coated, plated or painted.

Assuming you have brass parts, clean the brass with a commercial cleaner. This requires a trip to a good hardware store or to a commercial cleaning supplier. Howard Products Pinola Copper/Brass Polish is one of the best brass cleaners. Some others require coating the brass with a strong cleanser, then polishing and rubbing. Pinola Copper/Brass Polish is an easy-on, easy-off solution to tarnished brass or copper.

After the brass is clean and polished, for future protection there requires a neutralizer. Once the brass is clean and polished, you can also coat it with Howards Feed-N-Wax or Citrus Shield Paste Wax to prevent future tarnishing.