Don’t put cold liquid in a hot crystal glass. Or wash a cold crystal glass in very hot water. It might shatter.
Blindfolded, I can tell the sound of clinking crystal glasses (rather than glass) at a classic toast of champagne glasses… The sound is clear, sharp, and frankly, “expensive” when compared with glass. Lead crystal (the percentage of lead in glass that makes it “crystal differs from place to place) leads to a heavy, but beautifully clear glass (hence the phrase “crystal clear”) that absorbs and reflects light (particularly candlelight) beautifully. Probably unhealthy for you if used three times a day, lead crystal is fine for that every once in a while special occasion.
It seems counter-intuitive that something like glass with a high “lead” content might be more fragile than regular glass, but it is. Crystal has a horrible penchant for chipping and shattering when hit against other materials (including other crystal glasses) so you need to be extra careful when storing, using, cleaning and moving your crystal.
The photo: Harcourt Saucer Champagne by Baccarat. Yes, the champagne will taste the same in a plastic glass, so this is totally non-essential. But it is stunning to hold, behold and drink from. :)