[Random] Old cathedral windows being thicker at the bottom does not mean glass is secretly a liquid

[Freddie_47]

A popular myth claims that centuries old church windows appear thicker at the bottom because glass is technically a liquid that slowly flows downward under gravity over hundreds of years. It's a compelling story, but it's not true. Glass is properly classified as an amorphous solid, meaning its atoms are frozen in a disordered, jumbled arrangement similar to a liquid's structure, but locked rigidly in place rather than actually flowing. University of Wisconsin chemistry professor Mark Ediger notes that while glass technically can flow given enough time, that flow happens at a rate so slow it's essentially meaningless on any human timescale, at room temperature, a typical piece of window glass would take roughly a billion years to change shape by less than one nanometer.

The real explanation for those uneven old windows comes down to manufacturing, not physics. Medieval glassmakers often produced window panes using a spinning technique that naturally created discs of uneven thickness, and when installers cut and mounted those panes, they commonly placed the heavier, thicker edge at the bottom purely for structural stability, not because gravity had pulled it there over time.

Fact or Fiction?: Glass Is a (Supercooled) Liquidwww.scientificamerican.com

[Dom_24]

A billion years to shift less than a nanometer is such a perfect way to illustrate exactly how meaningless the technical flow claim actually is in practice

[WanderingSentinel]

The manufacturing explanation is so much more satisfying than the myth, installers just putting the heavier edge down for stability makes complete practical sense

[Dataset Isaac]

Amorphous solid is an useful category I didn't know existed, that in-between classification explains a lot about why this myth persists so stubbornly

[Shazam]

This is a great example of a scientifically plausible sounding explanation being wrong while the actually correct answer is more mundane but ultimately more interesting

[Pilot]

Good reminder that ancient Egyptian glass vessels don't show this same sagging pattern despite being even older, which alone should have debunked this myth much earlier

[DiogoCardoso]

Explains why this specific myth keeps getting repeated in science classes even though actual glass physicists have been correcting it for decades now