Copper (Cu29) removes toxins from the body and kills bacteria. Visual evidence of this is seen directly on the metal, i.e: metal turning dull or very dark even black at times. Thus the metal requires cleaning. (this coloration is a strong indication to change your diet and drink more water). At Simitre, we simply use real lemon juice (in the GREEN bottle) to clean our copper and our brass (not silver).
Instructions: Add Lemon Juice (no water) to a container with a lid. You can save it in the refrigerator for future cleaning. Let jewelry soak until copper begins to brighten up, about 2-3min. Remove from lemon juice & rinse with cool water. Dry with a soft cloth. Buff with a jewelry polishing cloth that is specifically used for silver and gold. NOTE Do Not soak over night!!
Please NOTE: Being that the acidity in lemon juice cleans copper, this also means lemon juice will clean any copper-based crystal that is mounted to any jewelry. These copper based crystals can not touch or be submerged in lemon juice like the jewelry. In this case you would need to dampen a piece of cloth with the lemon juice and wipe only the copper/brass with the cloth and NOT the crystal/stone.
List of copper based crystals include:

Azurite, Malachite, Turquois, Diaoptase, Smithsonite, Chrysoclla, Crussite, Rhodocrosite, Shells (Abalone/Pearl/Coral) to name a few.