Brass and bronze are beautiful, *much more* affordable alternatives to solid gold jewelry. For pieces that are cast in a mold, gold filled is not an option, which is why jewelers have to choose among brass, bronze, or gold plated for their more affordable options.
The reason these metals are more affordable, however, is that they are much more reactive to the elements than fine metals, and can tarnish quickly if not cared for properly. The good news is, as opposed to brass jewelry that has been plated with gold that will eventually wear off, non-plated pieces can be cleaned easily to maintain their beautiful gold luster.
CARING FOR YOUR BRASS JEWELRY
Try to avoid contact with water and chemicals (bleach, perfume, bug spray, sunscreen, etc). This will cause your brass jewelry to oxidize faster.
Wearing and touching your brass pieces will actually help prevent tarnish. Ever see a statue in a park where a part that is frequently touched is much brighter? That's because the natural oils/acids from our skin do help rub off and delay some tarnish.
When not in use - I cannot stress this enough! - keep your brass jewelry is dry and sealed in a plastic baggie. Try to squeeze out as much of the extra air as you can. Bonus points if you include an anti-tarnish strip in the bag ( you can get them on Amazon here ). This tip also applies to any sterling jewelry, but is less necessary.
CLEANING YOUR BRASS JEWELRY
Obviously it's impossible to avoid contact with water and the air, and you will need to occasionally clean your brass jewelry. I exclusively use Sunshine Polishing Cloths (you can buy them here or on Amazon. But make sure they're yellow and Sunshine brand!). These are the best polishing cloths on the market, and they work wonders on any metal. I include a tiny one with all of my brass orders.
While you can use a brass cleaning liquid, sometimes I find that pieces tarnish more quickly when you take that route, so I ultimately recommend taking the time to occasionally buff your jewelry with a Sunshine Polishing Cloth right before you wear your jewelry.