Glaze material · Clays
Calcined kaolin
Also sold as: Glomax, calcined EPK
Kaolin that has already lost its chemical water — same alumina and silica, without the drying shrinkage.
In published recipes
Used in 285 of 10,859 glaze recipes (2.6%)
Typical amount when present
12% of the dry batch — half of recipes fall between 7.1% and 19.1%.
Fired surface of those recipes
Glossy 44% · Matte 26% · Smooth matte 17% · Semi-glossy 13%
Most often mixed with
Materials that appear in the same recipes most often.
Chemistry
- Fired formula
- Al2O3·2SiO2
- kaolin with its chemical water already driven off
From Linda Arbuckle's materials table. Mineral formulas are idealized; buy an analysis for the bag you have. Equivalent weight is the weight that supplies one molecule of the fired oxide — the number glaze calculation uses.
What potters should know
Used in place of part of the raw clay when a glaze cracks or crawls as it dries: less shrinkage on the pot before firing, same fired chemistry.
Handling and safety
Crystalline silica: the primary respiratory hazard in a ceramic studio (silicosis with chronic exposure). Wet processes, ventilation and a fitted respirator when dry.
Dry ceramic materials generate respirable silica dust. Use a NIOSH-approved N95 or P100 respirator and adequate ventilation when mixing dry, and wet-clean surfaces.
This information is provided for planning purposes and is derived from publicly available sources including OSHA regulations, NIOSH guidance, and manufacturer safety data sheets. It does not constitute professional safety advice. Consult your material suppliers' SDS documents and applicable local regulations for authoritative safety guidance.
Questions
- How much Calcined kaolin do potters use in a glaze?
- Across 285 published glaze recipes containing it, the typical amount is 12% of the dry batch, with half of recipes between 7.1% and 19.1%. Colorants and additives sit far lower than fluxes and glass formers; treat these as a range to test around, not a target.
- What cone is Calcined kaolin used at?
- It appears in recipes across the range; the most common cones among published recipes are cone 6, cone 10, cone 5. Where a material sits depends on the rest of the recipe more than on the material itself.
- Is Calcined kaolin safe to use?
- It carries no specific hazard flag beyond the general rule for all dry ceramic materials: avoid breathing the dust and read the supplier's SDS.
Sources. Usage figures are computed by Claybench over 10,859 glaze recipes compiled from publicly shared community recipe collections (snapshot 2026-02-27) — counts only; no recipe is reproduced, and the figures describe that collection, not every recipe in existence. Material roles and notes are paraphrased from Linda Arbuckle's Ceramic Materials handout unless noted. Hazard notes summarise supplier SDS guidance; read the SDS for the product you buy.
Claybench tracks your glaze materials, not just recipes
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