brass is a yellow colored metallic alloy made of copper + zinc.
to keep your brass items beautiful, and your skin clear of possible irritation make sure to : always wear brass jewelry on top of your clothes. don't wear it directly on to your skin, make sure to sleep, shower, swim, perform household chores, sport without them.
brass will eventually change from yellow to brown over time. if you don't like this antique patina for your item you could make it shiny + new again with a polishing cloth. a transparant anti tarnish coating can protect the metal and slow down the process.
2,5 - 3 on the scale of mohs. glossy becomes a bit matte, matte becomes a bit glossy over time.