Brass and copper are soft materials that need to be carefully cleaned. Usually all that's required is washing with warm water and mild detergent and drying with a soft, clean cloth. However, when brass and copper become tarnished, some creative methods need to be used that will remove the tarnish without damaging your brass or copper item.
Use a chemical brass cleaner like English Custom Metal Polish and Restorer or a commercial copper cleaner like Copper Glo or Wright's Copper Cream. Make sure it's not an abrasive cleaner--you don't want to scratch the brass or copper.
Make a paste by mixing 1 cup of white vinegar with 3 tbsp of flour and 3 tbsp of salt. Put the paste on the copper or brass, rub it in and let it dry. Rinse it off with cold water and polish it with a soft, dry cloth. If you're out of vinegar, you can use lemon juice.
Soak brass and copper pieces in 2 cups of milk mixed with 2 cups of warm water. The lactic acid in the milk will remove the tarnish.
Mix 1 cup of lemon juice, 3 tbsp of cream of tartar, and 5 drops of orange oil to make a paste. Put latex or plastic gloves on and rub the paste into the brass or copper. Let it dry. Rinse the surface with warm water and dry it with a soft cloth.
Soak the brass or copper in Coca-Cola for two days to fade and loosen the tarnish. Use a soft toothbrush and Brasso Cleaner to remove the tarnish.
Rub olive oil into the brass or copper in a circular motion with a soft cloth after cleaning to keep tarnish away.
Spray a coat of clear lacquer like Krylon onto the brass or copper to protect it after tarnish is removed. Wait 5 minutes and add another light coat.
Don't use cleansers with ammonia as it can cause cracking, etching and premature ageing of brass and copper.
Don't use steel wool as it can scratch the brass and copper.