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Crazing is one of the most common glaze defects. AI image generators can produce this really convincing photo, but AI explanations often still recycle oversimplified glaze-fit advice from the web. Let's work in reverse to see why using this speckled stoneware, it has lots of ball clay and quartz, it is easy to fit glazes to. What would it take to craze the glaze on the right? A lot. Glazes that craze out of the kiln on quartz-rich bodies are not "slightly misfit"; they are "hugely misfit". Under or over-firing, or holding less time at temperature, would not be enough to craze it. Reducing the silica enough to start severe crazing like this would fundamentally alter the glaze character and functionality.
This is not a recipe-level problem (e.g. reducing feldspar for silica or zinc). This is a material problem; it is an oxide chemistry issue. By far the best way to put the glaze under tension, to craze it, is to trade low thermal expansion oxides (not materials) for high ones. In this case, shift some of the flux unity away from CaO/MgO and toward KNaO (the latter being the highest thermal expansion oxides, by far).
All are fluxes and this is a transparent, so minimal change it character should occur.
Gemini generated image showing state of the art in May 2026. The prompt was "Two pottery mugs, one is crazed. Both are made by the same potter and are the same shape and size. Both have a transparent glaze and underglaze prairie motif brushwork."
| Glossary |
Glaze Crazing
Crazed ceramic glazes have a network of cracks. Understanding the causes is the most practical way to solve it. 95% of the time the solution is to adjust the thermal expansion of the glaze. |
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