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AhaBulb: Stuff Everyone Should Know · ahabulb.com/glass-liquid

Is the glass in old windows thicker at the bottom because glass slowly flows down?

No, glass is a solid. Old manufacturing methods just made uneven panes.

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  1. Yes, glass is a slow liquid
  2. No, the window frames squeeze it
  3. No, glass is a solid ✔

Why: Hundreds of years ago, glassblowers spun glass into flat discs that were thicker at the edges. Builders usually put the thicker edge at the bottom for stability.

Huh, didn't know that: Ancient Roman glass looks exactly the same today as it did when it was made, proving it does not flow.

The dad joke
Why did the window go to the doctor? It was in a lot of pane.
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References

Answer: No, glass is a solid. Hundreds of years ago, glassblowers spun glass into flat discs that were thicker at the edges. Builders usually put the thicker edge at the bottom for stability.

  1. Corning Museum of Glass: Does Glass Flow? info.cmog.org/node/631
    Glass does not flow once it reaches room temperature.
    Checked 2026-10-09.

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