Care and Maintenance of a Horn

If you try to remove the mouthpiece by force on your own, you run a significant risk of damaging the mouthpiece or the instrument itself. It's much safer to leave this to a professional. Yamaha recommends taking your instrument to a repair technician when this happens.

Sometimes, the lacquer can begin to come off of parts of the instrument, including the part that comes into contact with your left hand, and the place that touches your knee when your rest it on your knee with the mouthpiece upward. When this happens, the brass is exposed and may begin to show discoloration. When this happens, you can use lacquer polish on the lacquered parts, and metal polish on the bare metal.
This discoloration, however, also serves to protect your instrument from any deteriorating further into rusting, and even if it doesn't look great, the metal will last longer if you leave it that way. You can normally use just lacquer polish, and then use some metal polish only when you want to give the instrument a metallic shine.

When rust forms in the threads that join a horn and its detachable bell, screwing the bell off or on will produce quite a sound.
If this happens, you can apply some new oil or grease to the threads. Before applying the oil or grease, however, be sure to gently wipe the threads clean with gauze or something similar. If grease or oil is applied while they are still dirty, the dirt will get stuck in it and can damage the threads.

Sometimes after playing, something greenish can appear on the horn where your left hand touches it. This is thought to be a type of verdigris, caused by the beginning stages of dissolution of the brass and nickel that make up the tube when they come into contact with sweat. It is not considered harmful to people, but it is better to wash your hands after playing, and avoid getting the verdigris in your mouth or eating anything with your hands directly after playing.
If it bothers you, you can go to a music shop and have them put a coating on it, or you can use a hand guard/protector, which are available on the market, and simply avoid touching it with your bare hands. Using a hand guard is the cheapest and easiest method.

All instruments have their own characteristic smells, and the horn is no exception. New horns smell like oil and the materials they are made of, and with use they begin to smell like the player's breath and verdigris, a type of rust particular to brass.
There are also times when the mouthpiece can start to smell because of accumulated dirt. It's a good idea to rinse the mouthpiece clean with water after practice or performances. If the mouthpiece is really dirty, you can clean it easily with a mouthpiece brush.