If you look through a pane of common window glass the way it was meant to be looked through, it's clear. But if you look at it from the side it's not very clear at all, but a dark green color.
One might think at first that this is due to thickness, that the glass is actually green (but highly translucent) throughout, but when looking straight through a pane it's thin enough that you don't notice the green color. But if you pick up a small piece of a broken window, a shard no larger than the thickness of a window pane, you can still see that it's transparent from one direction but dark green when looked at from the side, so clearly (no pun intended) it has to do with some property of the glass itself and the angle at which it's looked through, rather than the thickness of the glass.
Can anyone explain why the same uniform material has a radically different color depending on which way the light travels through it on the way to your eyes?
