"It's sometimes said that glass in very old churches is thicker at the bottom than at the top because glass is a liquid, and so over several centuries it has flowed towards the bottom. This is not true. In mediaeval times, panes of glass were often made by the "Crown glass" process. A lump of molten glass was rolled, blown, expanded, flattened and finally spun into a disc before being cut into panes. The sheets were thicker towards the edge of the disc and were usually installed with the heavier side at the bottom. Other techniques of forming glass panes have been used, but it is only the relatively recent float glass processes that have produced good-quality flat sheets of glass." https://math.ucr.edu/home/baez/physics/General/Glass/glass.h...
"It's sometimes said that glass in very old churches is thicker at the bottom than at the top because glass is a liquid, and so over several centuries it has flowed towards the bottom. This is not true. In mediaeval times, panes of glass were often made by the "Crown glass" process. A lump of molten glass was rolled, blown, expanded, flattened and finally spun into a disc before being cut into panes. The sheets were thicker towards the edge of the disc and were usually installed with the heavier side at the bottom. Other techniques of forming glass panes have been used, but it is only the relatively recent float glass processes that have produced good-quality flat sheets of glass." https://math.ucr.edu/home/baez/physics/General/Glass/glass.h...