Thermal shock
Cool one part of a hot solid faster than the rest and the resulting stress can crack it. The reason every stove glass instruction begins with waiting.
In detail
When a solid is heated it expands, and when part of it is cooled abruptly that part contracts while the material around it has not yet caught up. The result is internal stress, and where the stress exceeds what the material can carry, it cracks. Glass is particularly exposed to this because it is stiff and brittle and cannot relieve stress by deforming. Glass-ceramic of the kind used in stove doors and ceramic hobs is engineered specifically to resist it, by having a very low coefficient of thermal expansion so that a temperature difference produces very little dimensional difference — which is precisely why it can sit between a fire and a room. Engineered resistance is not immunity, and the manufacturers do not treat it as such: the instruction to let the glass become cool to the touch before cleaning, and the specific warning against spraying water onto hot glass because it could crack or shatter, appear in both the trade body's guidance and the manufacturers' own. The same principle explains a set of otherwise unconnected domestic accidents, from cold water into a hot pan to a hot dish onto a cold stone worktop.
Why
- Stove glass is explained by Thermal shock
- Microwave turntable is explained by Thermal shock
Sprint 27. Why the timing is the instruction rather than the water.
- Fridge shelf is explained by Thermal shock
Harvested rather than acquired: the catalogue has modelled thermal shock for stove glass since Sprint 1, and a chilled shelf under hot water is the same mechanism running the other way.
Sources for this page
Sources
Top tips for keeping your stove glass clean
HETAS Limited, United Kingdom · Trade or professional body
Relied on for: That the glass must be cool to the touch before cleaning to avoid the risk of it shattering. (states this directly)
Verification: a person has read the passage relied on.
Read on — The whole article: cleaning technique, cautions, and prevention. Supports a wider statement — our claim was widened. This materially upgraded the ash-on-stove-glass claim. Sprint 1 recorded it as practitioner practice supported by mechanism alone, with a verification target noting that if HETAS said nothing about glass cleaning the claim should rest on practitioner practice alone. HETAS says a great deal about it, recommends the technique directly, and supplies the cool-glass prerequisite and the ash-grit caution that CleaningHQ had inferred. The claim's support level was raised and its conditions are now sourced rather than reasoned.
How to clean wood burner glass
Charnwood (A J Wells & Sons Limited) · Manufacturer documentation
Relied on for: That spraying water on hot wood burner glass could cause the glass to crack or shatter, and that cleaning must not be attempted while the surface is hot. (states this directly)
Verification: a person has read the passage relied on.
Read on — The cleaning method, the cautions, and the soot-prevention section. Supports the claim as stated. Provides manufacturer-tier support for the ash technique alongside HETAS, and — more usefully — demonstrates that the same document can prohibit abrasive cleaners and recommend an abrasive powder without contradicting itself. That tension is now recorded as an evidence conflict rather than resolved silently in either direction.
Kirk-Othmer Encyclopedia of Chemical Technology
John Wiley & Sons · Reference work
Relied on for: That glass-ceramics are engineered for low thermal expansion in order to resist thermal shock. (background and mechanism only)
Verification: the work exists and is described correctly. Nobody has yet read the specific passage.
Last reviewed by a person on .