The first thing you need to know is whether it is solid brass or just brass plated.
Scratch the backside of a hinge or a hidden part of your brass piece. If you see a different metal under the coating, it is brass plated. If a deep scratch, or even a bit of grinding reveal no different metal, it will be solid brass.
You also get an indication by the brass being significantly heavier than steel plated "brass". Why is this important? Because the easiest way to cleanly remove layers of paint on solid brass without scratching it is to simply soak it overnight in paint stripper. But don't try this with plated brass, you will remove the plating right along with the paint!
So solid brass -- soak in paint striper, wipe clean and polish with a brass polish.
Plated brass -- use a heat gun gently followed by very conservative use of strippers and soft cloths, followed by the brass polish. You have to work much harder to get plated brass clean without damaging the brass coating.