Fact
Glass is not a slow-moving liquid
Old cathedral windows are thicker at the bottom because of how they were made.
The claim that medieval glass has flowed downward over centuries is false; calculations show it would take vastly longer than the age of the universe to be visible. Crown glass was spun into discs of uneven thickness, and glaziers sensibly installed the heavy edge at the bottom. Glass is an amorphous solid, not a liquid.