[Christ]

Originally Posted by jamesqf

Not so. Most non-metallic crystals (and crystals by definition are true solids) will transmit light. Quartz crystals, salt, sugar, diamond... Every individual crystal transmits light, it's the reflections off the myriad non-parallel surfaces that gives the bulk material its white appearance.

As for the "old glass is thicker at the bottom because it flows" myth, that comes from old stained glass windows in European cathedrals (some of which might be close to a thousand years old). But the window makers were just (quite sensibly) putting in the glass with the thick ends down.

There are likewise glass objects - beads and such - from archeological sites, and natural volcanic glasses such as obsidian. If glass did flow enough to be noticed in American windows that are only a few hundred years old at most, why haven't these much older glasses dribbled away?

Good point. I'm not sure where I got that from?