The point about hot water, cold sprays, etc, is to remember the basic physics. The metal tube will expand and contract more than the plastic mouthpiece, which is OUTSIDE it. So with the hot water, the trick is to get more of it on the plastic - which conducts heat slowly, and if using cold, to get more of it on the metal, which conducts heat rapidly. If you put too much heat on the metal, you may crack the plastic mouthpiece.

If you warm the mouthpiece end up, then rub an ice cube on the metal near the plastic, you get the best of both. The idea is to crack the seal between the glue and the metal - the glue will let go of the metal if enough stress is put on it.

If you look up very old 'recorders' in museums, you find that the older ones look almost identical to 'whistles' - the number of holes is idential - they are both 'flute-a-bec' - as distinct from 'flauto-traverso' which grew into the moderm flute when Mr Boehm had finished with it.

Why do schoolkids playing those cheap plastic recorders always sound shrill? They are overblowing, which raises the pitch.

Robin