Glass isn’t just SiO2

It happened so long ago that it’s not really known how glass was first discovered. Certainly, lightning can strike a sandy beach and fuse silicon into glass bits (called fulgurites). The lightning has to reach 3270 F for this to happen, which would be difficult for ancient human cultures to reproduce, although there are tales of sailors inadvertently using sodium carbonate blocks around a fire ring on the beach, which reduces the melting point of glass to 2552 F, more likely to be within reach. According to wikipedia, a candle flame reaches about 1800 F, and a blowtorch gets up to 2370 F, and a Bunsen burner can get up to 2900 F — so chemistry lab students out there should be able to get right to work on glass-making!

Interestingly, glass made with sodium carbonate (also called niter) isn’t very stable; it gradually dissolves from contact with water (which makes terrible windows or water glasses). More stable glass can be made by adding calcium carbonate (lime), which is what is still done today. Other additives create color tints and other properties. Here are some glass recipes with suggested proportions. The wikipedia article on glass is full of other fascinating tidbits.

And yes, glass is generally considered to be a solid (albeit an amorphous one, meaning it has no crystalline structure) rather than a liquid.

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  1. Judson said,

    January 30, 2011 at 9:08 pm

    (Knew it already.)

    (Current) favorite glass trivia: modern window glass is made by pouring puddles of molten glass onto moving streams of molten tin – the glass finds it’s level on top of the level tin, and then cools to be hard enough to remove. The result is a smooth pane. Much better than, say, pulling a blob out of the furnace and turning it into a big disk which you then cut into small panes which are then used to (erroneously) claim that glass is some kind of fluid. (That would be He3)

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