RSSTheodore Gray @ PopSci writes -
All the components of glass can be found in two places: the beach and the laundry room. It’s possible to melt pure white-silica beach sand into glass, but only at temperatures of 3,000 to 3,500°F. Washing soda, lime or borax (a traditional laundry aid) added to the sand disrupts the quartz-crystal structure of silica and reduces the required temperature to a more practical, though still dangerous, 2,000°F, which I achieved with a backyard grill and a vacuum cleaner. Glass is thought to have been discovered around 7,000 years ago by Phoenician merchants when cooking fires were built over sand that, by chance, had some of these substances mixed in.
This is a great quick-and-dirty approach.
But if you want to get useable glass, or even make more than one batch without destroying your grill (and incidentally creating a ton of landfill!) I recommend the Dave Gingery Charcoal Foundry:
http://www.lindsaybks.com/dgjp/djgbk/char/index.html
It's originally designed for melting metal, but ours melted glass just as well. It is very similar to this grill design.
The major difference (aside from using a trash can instead of a grill) is that it is lined with a sand/fireclay mix, ingredients which you can get at any home supply store, like OSH. The fireclay is designed for this precise purpose, being next to very hot things without reacting. The trickiest part was making the foundry lid from fireclay, so it wouldn't melt.
A friend and I built the Trashcan Foundry in my parents' backyard. For fun we also used coal (instead of charcoal) for a more "O G" Industrial Revolution feel. Steampunk represent!!
Dave also wrote an entire library of books aimed at building a fully-stocked machine shop from scrap metal. I haven't quite gotten to that point, but the foundry worked excellently.
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