How is a glass made?

Glass is essentially silicon dioxide (the most common, but other minerals are used for special purposes) melted to a liquid and then cooled in such a way as to not form crystals, but a disordered structure. The previous poster was right: sand is mostly silicon dioxide.

To make plate glass, people take this molten glass and float it onto a molten layer of metal! The glass is then rolled off the pool of molten metal to cool and form sheets, which is how they can make glass so flat.

For a cool demonstration of how people used to make things out of glass, check out this video:

YouTube.com/watch?v=Ny1S5K3Zm3Q&feature=related">http://www.YouTube.com/watch?v=Ny1S5K3Zm3Q&feature=related