Copper begins to oxidize, lose its luster and turn brown when wet so protect from water, sweat etc. If this happens, to restore your copper piece’s shine, simply let it soak in lemon juice for a few minutes, then a water and dish soap mixture for a few more minutes. Lastly, rinse with clean water and dry thoroughly. For silver and gold, use lime juice instead of lemon and follow the same steps as above. Be cautious of the type of stone to ensure it can get wet.