Speaker 1: Welcome to brain Stuff production of iHeart Radio. Hey brain Stuff.
Speaker 1: Lauren vogel Bomb here with today's question. Is glass a
Speaker 1: liquid or a solid? If you've ever looked the window
Speaker 1: panes in an old building, you may have noticed that
Speaker 1: the glass was rippley and thicker towards the bottom of
Speaker 1: the pane, and you might have leaped to the logical
Speaker 1: sounding conclusion that the glass had flowed into that shape
Speaker 1: very slowly, over a couple of centuries. That while the
Speaker 1: window frames are solid wood and metal, the glass is
Speaker 1: a liquid, oh if a highly viscous, very slow flowing one.
Speaker 1: You might have even heard this explanation from a teacher
Speaker 1: or read it in a textbook. The truth, however, is
Speaker 1: that the glass has always been that way. Okay, So,
Speaker 1: up through the eighteen hundreds, panes of glass were made
Speaker 1: by hand. Glass blowers used what's called the Crown process.
Speaker 1: Here's how it works. That take a flattened bubble of
Speaker 1: very hot glass and rotate it so fast that centrifugal
Speaker 1: force would spin it out into a large, mostly flat disk.
Speaker 1: The disc would be thicker at the edges, and each
Speaker 1: pain cut from it was bound to be a little
Speaker 1: bit lumpy, and workers tended to install them with a
Speaker 1: thicker side down, probably because the slightly larger edge provided
Speaker 1: better balance. So the glass in those old panes isn't
Speaker 1: flowing at least not that researchers can discern. They've looked
Speaker 1: at samples of glass from two thousand years ago and
Speaker 1: haven't found any telltale evidence of flow. So glass is
Speaker 1: not a liquid, but it's not a normal solid either.
Speaker 1: Scientifically speaking, glass is considered an amorphous solid. That means
Speaker 1: it's atoms and molecules are locked into place, alike in
Speaker 1: a solid, but those molecules are arranged more randomly than
Speaker 1: in most solids, a more similar to a liquid. If
Speaker 1: you wanted to get into semantics, you could sort of
Speaker 1: call glass a super cooled liquid. That's a liquid that's
Speaker 1: been cooled below it's melting point carefully so that it
Speaker 1: doesn't crystallize, and that's part of making glass. In its
Speaker 1: liquid stage, glasses hundreds of degrees above room temperature. It's
Speaker 1: then cooled rapidly and carefully in a process known as quenching,
Speaker 1: until it transitions into the rigid, amorphous solid that we
Speaker 1: know and love. So you might say that glass is
Speaker 1: its own state of matter. Neither a liquid nor a solid.
Speaker 1: Today's episode was written by me and William Harris and
Speaker 1: produced by Tyler Clay. For more on this and that's
Speaker 1: of other translucent topics, visit how stuff works dot com.
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