The structure of glass is, frankly, a bit of a mess. Clear and perfect as it might appear to our eyes, down at the molecular level, glass looks more like a random ball-pit of atoms. The technical term for this mess depends on who you’re asking: for some scientists it is an “amorphous solid,” for others a “supercooled liquid.” In theory it’s both liquid and solid, though, given the way it behaves, in practice it’s really the latter. In fact, at room temperature glass never behaves as a (a) liquid even an imperceptibly viscous one, even over long periods of time (though it can “sweat” if you don’t add enough lime to the mix). Those (b) misshapen sheets of glass you sometimes see in old stained-glass windows, thicker at the bottom than the top, are generally not that way because the glass is slowly sinking over time. Unless the church has endured temperatures of more than 400˚C, the chances are they are uneven because that’s the way they were blown and (c) solidified in the first place. Flat glass was only developed in the nineteenth century and we had to wait until the middle of the twentieth century for truly flat, thin sheets of glass. The (d) paradox is that, despite it being one of the very oldest human-made substances, scientists still struggle to comprehend why glass behaves the way it does. Glass seems to (e) obey most molecular laws. As one glassmaker put it, glass is not a material; it’s a state.
* molecular: 분자의 ** amorphous: 무정형(無定形)의 *** viscous: 들러붙는