I have never used CLR for horn cleaning, but have heard of some techs using diluted "The Works" toilet bowl cleaner. Another product out there that a lot of techs are staring to use with good results (I haven't had a chance to try yet) is a diluted solution of "Mineral Shock." The guys I've heard from that use it really love the way it works. You have to dilute 4:1 or something. However, you have to be careful with any of that stuff - most will remove calcification to some degree, but if a lacquered horn is left too long in too strong a mix , then the lacquer will lose integrity (as I said before, also never rinse a lacquered horn with HOT water). But, I would guess most guys and gals on this forum with their own horns have silver-plated instruments, and you can't do much damage to that finish that a little silver polish and elbow grease won't cure.