I primarily use ammonia vapor. Parts suspended in a container with ammonia in the bottom. Be careful with thin parts however, as it will make things brittle. I'll leave things in a couple hours or a bit more. This puts a greenish tarnish on the brass, which can be rubbed back with burlap or steel wool to get brown underneath. Don't let ammonia touch the brass directly or you'll get uneven tarnish and corroded brass.
TOF, neat tip about the green hazelnut.
-Eric