I use a few things depending on the level of grime. For horns that haven't been cleaned in a long time, I will use a light abrasive cleaner like Wright's copper cream. For cleanings in between I will use a polish like Flitz or Maas. Drying is the most important thing after cleaning, and keep a rag around to wipe any moisture or fingerprints before they being to tarnish.
Re: Cleaning Unlaquered Brass? 22:24 on Saturday, December 02, 2017
Mr. Medlin is a great maker, and these products clean well. I am a fan of high quality vintage horns, often can find great value (Custom 1967 Paxman Double Descant for 2000 for example) and they are often horrid looking. I have a great shop a few cities over that I have been using to repair my instruments since the 70's and trust them very much. The brass repair folks there to a person say that once there has been an initial cleaning, try not to use any chemicals or polish, since you'll be removing metal. It was explained to me that the patina actually protects the brass from further deterioration. They also recommend that those places that we touch most though, be covered, so a wrap for the left hand and lacquer in the bell. I've never been a fan of shiny and don't care if my horns are a little funky, so if you want bright, I'd recommend just having it cleaned and re-lacquered.