What makes glass transparent?

Another really interesting and mind-bending question we discussed, is Why is glass transparent?

I know that glass is sand, and when mixed with extreme heat, such as lightening, glass can be produced (and through this way of making glass you receive really cool shapes)...

However what makes it transparent?

Things such as paper reflect light, and absorb it, so does glass simply...? I don't even know....

Image: http://madebymeg.net/blog/sea-glass-made-from-lightning/

What I found was really cool, it turns out that glass is transparent partially because it does not absorb visible light rays. However, I discovered that if light is high energy like deep-ultraviolet, then it CAN be absorbed by glass, making the glass seem opaque, and not transparent to high energy rays.

So the visual light spectrum cannot penetrate the glass, and therefore it appears "transparent" to human eyes.

"Glass is almost perfectly opaque to deep ultraviolet, which is why it's hard to get a tan through a window," emails physicist Louis A. Bloomfield of the University of Virginia. "By deep ultraviolet, I mean UVB and UVC."

"Pure glass cannot absorb visible light. Light merely slows (as glass molecules decide what energy contained in visible light, if any, matches an energy level of an atom in the glass molecules). In fact, the speed of light through glass is 66% of its speed through a vacuum."

"Visible light from the Sun is made of light waves with many colors (which we see displayed in a rainbow, for example). Each color has a particular frequency and that frequency has an energy level proportional to that frequency, says Bloomfield.

What has to match is an electron's and a color's energy levels. If any of the energy levels of the light matches any of the energy levels of the electron, the electron absorbs that energy and the glass heats up.

But It turns out that none of glass electron energy levels match any of the energy levels in the colors of visible light. So light passes through glass. Thus, sun-illuminated pure glass doesn't get hot while the opaque frame around it does." http://www.happynews.com/news/1262010/glass-transparency.htm

This makes sense, because although windows on a car get warm-ish (most likely not being pure glass) they remain much cooler than all the other areas of the car.... I'm starting to understand the idea. So because the energy levels of the atoms in the class, do not match up with the energy levels each color has, it cannot absorb it... but the higher energy colors, that are invisible to the human eye do match.

So technically like color, the transparency of glass is all in our mind, because if we were able to see the UV spectrum it would be opaque like other solids..... Which is a little trippy, because one day if there is a mutation in human genetics and someone is able to see UV spectrum light, then all glass will be opaque, making life as we know it extremely difficult...