Old glass windows are not thicker at the bottom because glass flows — they were just installed that way
A persistent myth holds that glass is a very slow-moving liquid, and old window panes prove it because they're thicker at the bottom. Both claims are wrong. Glass is an amorphous solid — it does not flow at room temperature on any human timescale. The reason old windows are thicker at the bottom is simply that medieval glassmaking techniques produced uneven glass, and glaziers sensibly installed the thicker edge downward for stability. Modern analysis of ancient glass shows no measurable flow over thousands of years.
This myth appears in chemistry textbooks and authoritative sources, cited as a charming scientific curiosity. Its persistence despite being wrong is itself a lesson in how plausible-sounding explanations can survive in education long after they've been debunked.
“Old windows are NOT thicker at the bottom because glass flows slowly. Glass is a solid. Medieval glaziers just installed the thicker edge down for stability. This myth appears in textbooks. 🪟 #OddlyHuman”