Why glass is solid without being crystalline
In a crystal, atoms occupy an orderly pattern that repeats through the material. Glass lacks that long-range order: its atoms are arranged irregularly, more like those in a frozen liquid. That structure makes glass an amorphous solid—solid in how it behaves, even though its atomic arrangement is not crystalline.
The word “liquid” in this comparison describes glass’s disordered structure, not a slow, syrup-like motion. At ordinary temperatures, glass is so resistant to flowing that any change in the shape of a pane over centuries is negligible. It can deform when heated, but that is a response to heat, not a gradual downward creep at room temperature.
The uneven panes have a manufacturing history
Older window glass was often made by spinning molten glass into a flat disc. The disc could be thicker near its edge than at its center, so a pane cut from it was not perfectly uniform. When fitting the pane, installers often placed the thicker edge at the bottom, where the added thickness could make the glass seem to have settled there over time.
But the pane’s shape was already uneven when it was installed. Its variation records the way it was formed and fitted; it is not evidence that the glass slowly flowed down the window frame.
Disorder is not motion
The distinction is easy to miss because “amorphous” can sound like “not quite solid.” In practice, atomic arrangement and material behavior are separate questions: glass’s atoms lack a crystal’s repeating pattern, while the material itself remains rigid under everyday conditions. A window’s old-fashioned waviness is a manufacturing fingerprint, not a frozen record of centuries of sagging.
