Back in Jr high school our band director instructed us to use Dawn dish wash liquid when cleaning our horns. I have always taken that to mean any liquid dish washing soap. I decided to clean my main horn yesterday and used Dawn for the first time in years. After getting it out of the tub I noticed that most of the dark water spots on the inside of the bell were gone. What few that were left are much lighter than before. The Dawn took spots off that my silver polishing cloth wouldn't touch. Seems as if that old man knew what he was talking about.