Glass Is Not a Slow-Moving Liquid
Glass is a hard transparent material. The story that old windows are thicker at the bottom because glass flows is false.
Glass is a hard, brittle, usually transparent material made by melting sand. The favourite myth about it is wrong: medieval windows are thicker at the bottom not because glass flows, but because *crown glass* was spun into discs of uneven thickness and glaziers sensibly set the heavy edge downwards. At room temperature glass would take longer than the age of the universe to flow measurably. Glass is an amorphous solid, with no crystal structure, which is where the confusion begins.
- A hard transparent material. *A pane of glass.*
- A drinking vessel. *A glass of water.*
- Glasses — spectacles. *Reading glasses.*
- Glaze — a glassy coating. *A ceramic glaze.*
- Amorphous solid — the technical description. *An amorphous solid.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | glass | Broken glass. |
| Plural | glasses | Wine glasses. |
| Adjective | glassy | A glassy stare. |
| Verb | glaze | Glaze the window. |
| Old English | glæs | Glass. |
- The window is double glazed.Building.
- He drank a glass of water.Vessel.
- Glass does not flow at room temperature.Correction.
Why old windows look uneven
- Crown glass was made by spinning molten glass into a disc
- The disc was thicker near the centre and thinner at the rim
- Glaziers cut panes from it and set the heavier edge down
- Not every old pane is thicker at the bottom, which disproves flow
- Modern float glass is made on molten tin and is perfectly even
Old English *glæs*, from a Germanic root related to a word for shining, in the *gl-* family with *glow* and *gleam*.
Does glass flow over centuries?
No. The uneven thickness of old windows comes from how crown glass was made, not from flow.
Is glass a liquid?
No. It is an amorphous solid: rigid, but without the ordered crystal structure of most solids.