Glass

Old cathedral glass panes are not thicker at the bottom because glass flowed like a Liquid. Glass is an Amorphous Solid, and visible sagging would take absurdly long. The uneven thickness is better explained by old manufacturing and installation practices.

Dropping molten glass into cold water creates "Prince Rupert's Drop." Its head deflects bullets, yet snipping its thin tail shatters the whole drop explosively. The rapidly cooled surface compresses the interior so tightly that one break destroys everything.