Copper is sensitive to air and oxidizes (tarnishes) faster in moist air. Coating with lacquer, if not being used for food purposes, helps preserve the finish.
Most pieces of decorative, modern copper are protected by a factory-applied, baked-on lacquer. Only dusting and an occasional washing with lukewarm, soapy water are needed to keep lacquered objects shiny. Never polish them and do not use an abrasive cleaner or steel wool to clean copper bottoms.
If your jewelry is not lacquered then you can use the following to clean/polish your copper jewelry:
Lemon and Salt or Baking Soda. Make a paste of lemon juice and salt, and rub with a soft cloth, rinse with water, and dry. Or use a slice of lemon sprinkled with baking soda. Rub copper with the lemon slice and rinse with water and dry. Vinegar and Salt. Pour vinegar over the surface Sprinkle salt over the acid and rub in the mixture. Rinse with warm water and polish dry.
Vinegar and Salt. If copper is tarnished, boil article in a pot of water with 1 tablespoon salt and 1 cup white vinegar for several hours. Wash with soap in hot water. Rinse and dry.
Tarnished Copper: Polish with a commercial polish for copper following directions on the container. Polish can be made at home by moistening salt with vinegar or lemon juice to make a paste for a bright finish or a paste of rotten-stone and olive oil for a dull finish. After polishing decorative items, spray with lacquer to preserve color if desired.
"Bronze Disease" also attacks copper. Use hot vinegar and salt, or lemon juice and salt, copper cleaner, or buttermilk to remove these patches of corrosion. After treating, wash promptly with soap and water, rinse and dry.
Contact me if you have an issue on your copper jewelry at email@example.com