WEBVTT - Is Glass a Liquid or a Solid?

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<v Speaker 1>Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff.

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<v Speaker 1>Lauren vogel Bomb here with today's question. Is glass a

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<v Speaker 1>liquid or a solid? If you've ever looked the window

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<v Speaker 1>panes in an old building, you may have noticed that

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<v Speaker 1>the glass was rippley and thicker towards the bottom of

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<v Speaker 1>the pane, and you might have leaped to the logical

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<v Speaker 1>sounding conclusion that the glass had flowed into that shape

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<v Speaker 1>very slowly, over a couple of centuries. That while the

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<v Speaker 1>window frames are solid wood and metal, the glass is

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<v Speaker 1>a liquid, oh if a highly viscous, very slow flowing one.

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<v Speaker 1>You might have even heard this explanation from a teacher

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<v Speaker 1>or read it in a textbook. The truth, however, is

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<v Speaker 1>that the glass has always been that way. Okay, So,

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<v Speaker 1>up through the eighteen hundreds, panes of glass were made

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<v Speaker 1>by hand. Glass blowers used what's called the Crown process.

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<v Speaker 1>Here's how it works. That take a flattened bubble of

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<v Speaker 1>very hot glass and rotate it so fast that centrifugal

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<v Speaker 1>force would spin it out into a large, mostly flat disk.

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<v Speaker 1>The disc would be thicker at the edges, and each

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<v Speaker 1>pain cut from it was bound to be a little

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<v Speaker 1>bit lumpy, and workers tended to install them with a

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<v Speaker 1>thicker side down, probably because the slightly larger edge provided

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<v Speaker 1>better balance. So the glass in those old panes isn't

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<v Speaker 1>flowing at least not that researchers can discern. They've looked

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<v Speaker 1>at samples of glass from two thousand years ago and

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<v Speaker 1>haven't found any telltale evidence of flow. So glass is

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<v Speaker 1>not a liquid, but it's not a normal solid either.

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<v Speaker 1>Scientifically speaking, glass is considered an amorphous solid. That means

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<v Speaker 1>it's atoms and molecules are locked into place, alike in

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<v Speaker 1>a solid, but those molecules are arranged more randomly than

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<v Speaker 1>in most solids, a more similar to a liquid. If

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<v Speaker 1>you wanted to get into semantics, you could sort of

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<v Speaker 1>call glass a super cooled liquid. That's a liquid that's

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<v Speaker 1>been cooled below it's melting point carefully so that it

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<v Speaker 1>doesn't crystallize, and that's part of making glass. In its

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<v Speaker 1>liquid stage, glasses hundreds of degrees above room temperature. It's

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<v Speaker 1>then cooled rapidly and carefully in a process known as quenching,

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<v Speaker 1>until it transitions into the rigid, amorphous solid that we

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<v Speaker 1>know and love. So you might say that glass is

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<v Speaker 1>its own state of matter. Neither a liquid nor a solid.

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<v Speaker 1>Today's episode was written by me and William Harris and

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<v Speaker 1>produced by Tyler Clay. For more on this and that's

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<v Speaker 1>of other translucent topics, visit how stuff works dot com.

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<v Speaker 1>Brain Stuff is production of I heart Radio. For more

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