Glass is an amorphous solid, not a liquid.
The myth about “old glass from church window panes being thicker on the bottom” comes from panes that were unevenly manufactured and placed with the thick part at the bottom to begin with.
You know what’s older than churches, though?
That’s Roman glass in that photo. Notice how none of those vessels are currently in the form of a puddle, or a clock in a Salvador Dali painting.
This has been a public service announcement. Thank you.