Jonathan,
The only problem with that approach is that most (I think about 99.9%?) glass is tempered in a chemical bath at elevated temperatures and it is not a thermal process that does the tempering but a chemical process, the elevated temps just speed the process up so it doesn't take weeks. Glass does go through a thermal process earlier in the manufacturing cycle, but this is annealling and it simply removes any residual stresses in the glass so it doesn't explode when touched.
It is the chemical infusion of "typically sodium" molecules that makes tempered glass non-recyclable AND places the outer layers of the glass into compression. Heating it may cause the sodium molecules to disperse back out of the glass if done in a sodium starved bath, but getting the chemistry right to do what you suggest would be difficult at best. I am not saying it can't be done, but lexan starts looking really good by the time you have busted your 4th or 5th corner cab window doing experiments. :rolleyes:
