[manveru]

The problem, if i remember correctly, is that you cannot control the purity of recycled glass very well. The last time I checked it was mostly used to lower the temperature needed for the furnace.

But if you want to make pure boro-silicate glass, you cannot tolerate much contamination of oxides, lime, lead, dolomite, salt, etc. or your glass will be tinted, full of bubbles, and possibly even cracks while cooling.

Even with the recycling system in Germany where you separate glass by color, people will not distinguish a soda-lime, boro-silicate, or lead glass. And I don't know a process that could extract the pure SiO2 from old glass (though I'd love for someone to jump in and tell me about a cheap method)