Before you clean anything, determine if you're working with solid brass or brass-plating. If a magnet sticks to it, it's brass-plated, but if not, you’ve got solid-brass. Using hot, soapy water and a microfiber cloth, clean and rinse. If that doesn't do the trick, you can even use ketchup or vinegar! Take precaution with plated items, though—polish too aggressively and you can remove the brass-plating.