“Glass Flutes do not expand with humidity, so their owners are spared the nuisance of tuning them.”
This seems wrong to me for three reasons:
A metal flute doesn’t expand with humidity either, but needs to be tuned because it expands and contracts from temperature. Wouldn’t a glass flute have the same problem?
Tuning a metal flute isn’t exactly a nuisance. If anything, I would think that tuning a glass flute would be more difficult.
There are such things as glass flutes, and I’ve seen them in specialty music stores (although I’ve only ever heard them called “crystal flutes”). They’re not big; the ones I’ve seen have been nowhere near the size of the familiar metal concert flute, though I suppose they could be made in any size. Here’s a link to a flute catalogue–close to the bottom, you can see a photo and description of “Celtic crystal flutes.”
As for the claim that crystal flutes don’t expand with humidity; well, as Ethilrist correctly points out, humidity would affect a wooden flute. Temperature would affect metal and glass flutes, but I seem to recall a high school science experiment many years ago that proved that glass does not expand nearly as much as metal does when the two substances are exposed to the same heat. Did anybody else do this experiment, and/or is that the case–that glass will expand, but not as much as metal?
Some comments based on personal experience: I’ve never played a crystal flute, but because of the small size of the ones I’ve seen, I imagine that when it comes to tuning, they would fall into a category like the pennywhistle (which I have played, many times)–you pick up the whistle that’s in the appropriate key, and off you go. Not really an instrument that requires careful and exact tuning, in other words, but one that’s more for having some fun with.
And if you are playing the kind of music that you can play pennywhistle to, and you are playing with a bunch of people who are having a great time, and if the audience (and the band) has had a few drinks, nobody notices if the pennywhistle, nor presumably the crystal flute, is a little out of tune.
Some glasses, like pyrex, have a very small coefficient of thermal expansion. On the other hand, the speed of sound itself changes with temperature, so what you really need is a glass whose thermal expansion properties are designed to compensate for the change in the speed of sound with temperature changes. I wouldn’t be surprised if some researcher somewhere has already come up this.