Scientists reveal why glass is glass

Scientists have made a breakthrough discovery in the bizarre properties of glass, which behaves at times like both a solid and a liquid.

The finding could lead to aircraft that look like Wonder Woman's plane. Such planes could have wings of glass or something called metallic glass, rather than being totally invisible.

The breakthrough involved solving the decades-old problem of just what glass is. It has been known that that despite its solid appearance, glass and gels are actually in a "jammed" state of matter — somewhere between liquid and solid — that moves very slowly. Like cars in a traffic jam, atoms in a glass are in something like suspended animation, unable to reach their destination because the route is blocked by their neighbors. So even though glass is a hard substance, it never quite becomes a proper solid, according to chemists and materials scientists. ... The deceptively liquid-like behavior of glass can be seen when you look at glass in the windows of an old building. The glass begins to sag and distort internally over the centuries, due to the effect of gravity. ... Royall is part of a group of scientists who think that if you wait long enough, perhaps billions of years, all glass will eventually crystallize into a true solid. In other words, glass is not in an equilibrium state, (although it appears that way to us during our limited lifetimes). - msnbc

Mystery: The molecular arrangement of metallic glass is now understood, but why does this metallic glass give off sparks when struck?

The alloy of zirconium, beryllium, titanium, copper, and nickel is one of the first metallic glasses that can be made in bulk and formed into strong, hard, useful objects. It was discovered by William L. Johnson and Atakan Peker of the California Institute of Technology. - lbl

The sample metallic glass above is obviously not clear. Is some metallic glass transparent?