Myth Buster – Are windows from cathedrals actually melting?

By: Akshaya, Science Expo Ontario

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Myth:
You’ve probably seen medieval European cathedrals and have observed the glass. You’ve probably assumed that glass is a liquid, and that since it was hard, you must have assumed further that it was a “super cooled” liquid. This was probably all from internet myths that even chemistry teachers might’ve believed, because the glass panes were thicker at the bottom in medieval windows. Glass, believe it or not, is neither a “super cooled” liquid nor solid!

The Science Behind it:
Glass is an amorphous solid – basically, a state in between liquid and solid. However, this still doesn’t explain the thicker bottomed window because the particles in glass move too slowly for visible changes to occur. This is because solids have a highly organized particle structure, and the millions of atoms are lined up in rows. In that sense, glasses and liquids are both a little disorganized, but amorphous solids are more organized than liquids, but don’t have as rigid of a structure as solids.

When glass is made, the material is cooled from its liquid state quickly, but it doesn’t become a solid when its temperature becomes cooler that a melting point. Technically, the material could be called a “super cooled” liquid, because it’s an immediate state between liquid and glass. For it to become an amorphous solid, it needs to be cooled even more. At this point, movement of the material’s particles slows down and it becomes a glass. Glass is a solid for purposes such as holding a drink, but it’s a disorganized one.

Because it is a disorganized solid, glass can flow a little, extremely slowly. A mathematical model shows that it would take longer than the existence of the universe for room temperature glass from a cathedral to appear melted.

So clearly melting isn’t an option, so you’re probably wondering why the cathedrals look like they’ve been melting. It was most likely because the glass pieces were never all uniformly flat, and the builders decided to put the thicker ones at the bottom of the windows for better support. Looks can be deceiving, and glass certainly isn’t a liquid.

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