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Crackle glaze, craquele

A type of glaze that is intentionally crazed. Stains and other colorants are often rubbed into the crack lines to heighten the effect. Crackle glazes almost always have very high KNaO (to raise the thermal expansion). These high levels push the contents of other fluxes abnormally low or completely exclude them. Crackle glazes also have lower Al2O3 (sometimes very low). Thus they will have fluid melts and tend to run. It is common to find high amounts of Ferro Frit 3110 (or similar frits) in the recipes, up to 90%. These recipes are employed all the way from Raku to cone 6 (obviously melting more as the temperature increases).

Crackle glazes typically severely weaken ceramic ware, especially if it is thin. The chemistry profile of these glazes also make them inherently susceptible to leaching of any added metallic colorants. Do not use them on food surfaces without careful leach testing.

Out Bound Links

  • (Glossary) Crazing

    Crazing refers to small hairline cracks in glazed surfaces that usually appear after firing but can appear years later. It is caused by a mismatch in the thermal expansions of glaze and body. Most ceramics expand slightly on heating and contract on cooling. Even though the amount of change is very s...

By Tony Hansen

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