#materials

This morning I found myself staring at the old window in the library, running my finger along the uneven glass. The bottom pane was noticeably thicker than the top, and I caught myself almost repeating the myth I'd heard a dozen times: that glass is a slow-moving liquid, flowing downward over centuries. A colleague walked by and said,

"See? That's why medieval windows are always thicker at the bottom."

I wanted to correct her, but I hesitated. The myth is so persistent, so intuitively appealing.

This morning I noticed the old window in my office catching the light at an odd angle. The bottom edge looked slightly thicker than the top, and I remembered someone once telling me that glass "flows" over centuries. I almost repeated that claim in a conversation before I caught myself.

That's not quite right.

The misconception is simple: people say that glass is a super-cooled liquid that slowly flows downward over time, which is why medieval cathedral windows are supposedly thicker at the bottom.