Raw brass will tarnish over time, deepening in colour. Some folks like this look, but if you want to get your brass bright and shiny again, you can use a polishing cloth.
Gold Fill vs. Gold Plated
Gold filled is created by pressure bonding a layer of gold to another metal, and therefore it will not tarnish over time. Gold filled and sterling silver are said to be hypoallergenic. Gold plated is made using electricity or chemicals to deposit and bond a thin layer of gold over another metal. The plated pieces that I carry are nickel free. Gold plated jewelry can tarnish over time, and that's why it is so important to take care of your plated pieces!
Sterling silver will inevitably tarnish over time. Using a polishing cloth is the easiest way to get your silver nice and shiny again.
How to clean and care for your pieces
The best way to ensure longevity of your pieces is to keep them in a cool, dry place. I would advise against wearing our plated and brass pieces in a moist environment. Even heavy lotions and perfumes can cause jewelry to tarnish more quickly. Salt water and water containing chlorine is especially harmful towards metal jewelry, as they will corrode your metal and leave it looking less-than-perfect.
If you do notice that your pieces are starting to tarnish, a polishing cloth is the easiest and most cost effective way to clean your pieces. If your jewelry needs more cleaning you may clean it with warm, soapy water. Soak it for a few minutes and you may clean it with a soft brush. Stay away from jewelry cleaners and antibacterial soaps which may have certain components that will just make your gold plated jewelry tarnish more quickly.