You can also use a common grocery store product called 'Lime-Away' on anything brass including horns. Spray on and scrub with a toothbrush, rinse. Does not affect lacquer.
BTW, I wanted to say something about cleaning Rovners and this thread is as good as any other: yesterday I tried a new one, a 'Star Series', and it was dyn-o-mite! Anyway, I had used the old one for a long time so I decided to clean it up and keep it since it was still good. Basically you wash it down with soap and water, scrubbing with a toothbrush, then rinse and dry. I'm glad I cleaned it because at rehearsal last night the new one struck me as TOO much of a good thing so I got out 'old reliable' and used it. I have never seen so much effect from a ligature but I'm definitely keeping both of them. You can look at Rovner and see what the Star Series is, but I don't know the model on the old one. Its very similar to the Star but it has an oval-shaped opening on each side. It has slits in the fabric like the Star but only at the top on each side because of the openings.