In glass, fast crowds boogie to brittle end

Glass is clear, but the process by which it forms remains maddeningly opaque.

As a liquid hardens into a glass, its molecules become extremely sluggish—more so than expected at the temperatures or conditions of molecular crowding under which the process takes place. Moreover, the molecules remain disorderly even after solidification, unlike those in a crystal, where the molecules occupy a tightly bonded lattice.