Brass -

Brass is an alloy of copper and zinc that works great for jewelry because it has a lovely warm color, almost resembling yellow gold, yet it is tough and far more affordable.  The surface color naturally darkens with age, and this is sped up by contact with skin.  Natural body oils and chemicals found in body products will also slowly add to the patina and dull the polish on your piece.  If you want to maintain the polish, I recommend removing your brass jewelry before washing, swimming, sleeping, or sweating.  It can be polished again using an all-purpose jewelry polishing cloth, or even brass polishing solution, which can be found at a hardware store.

Brass can sometimes create what's known as "skin staining" on some people, when a green mark is left on the skin after extended wear. This is a non-toxic reaction and it is not an allergy.  It has to do with skin chemistry, and is more likely to happen to people with higher acidity levels in their skin or during hot and humid conditions.  The humidity causes oxides to form from the copper in the brass, and this gets rubbed off onto the skin in the form of a green stain.  If your brass ring is big and chunky, or too tight for you, the chance of staining is greater as there is more moisture to get trapped under there.  But again, the staining is natural and non-toxic, and can be removed with soap and water.


Sterling -

Sterling is made of 92.5% pure silver and 7.5% of metal alloy, most commonly copper.  It is softer than brass and can scratch and bend if not worn carefully.  If you'd like to avoid surface scratches, I recommend storing your sterling piece in a separate pouch or box.  Keep it away from bleach, ammonia and chlorine products, which will tarnish it.  Remove your sterling before using household cleaners or swimming in chlorinated pools.  Eventually sterling will darken on its own, but the patina can be removed with a non-abrasive jewelry polishing cloth or tarnish-removing silver cleaner.