A Few Methods to Keep your Copper Jewelry  Clean: 

1) ketchup - Rub it in with cloth, Rinse with Warm Water & Dry

2) Lemon Juice- same steps as the Ketchup

3) Sea Salt & Apple Cider Vinegar - use 1/2 cup of ACV & 1/2 cup of sea salt & warm water. Make a solution, put jewelry in and shake! Rinse and towel Dry! (Best Results)

I also Recommend Jewel Brite Natural Cleaner or Tarnax for more detailed creations!