Raw brass is an alloy of copper and zinc. Raw brass can tarnish over time.  You can purchase sealant from Bunnings to help prevent tarnishing. There are many ways and tips on the internet to clean your brass components. My tip is to use vinegar (enough to cover components) baking powder (1 teaspoon) and lemon juice (1/2 teaspoon) mix in a small bowl, soaking the components for 1 minute, rinse in water then polish with a microfibre cloth.  I highly recommend cleaning your components before assembling your jewellery.  Pass this information onto your customers.