How much Cornwall stone do potters use in a glaze?

Across 330 published glaze recipes containing it, the typical amount is 37.3% of the dry batch, with half of recipes between 20.1% and 50%. 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 Cornwall stone used at?

It appears in recipes across the range; the most common cones among published recipes are cone 10, cone 6, cone 9. Where a material sits depends on the rest of the recipe more than on the material itself.

Is Cornwall stone 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.

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Glaze material · Fluxes, feldspars & frits

Cornwall stone

Also sold as: Cornish stone, D.F. stone

A feldspathic rock with more silica than feldspar — flux, glass former and alumina in one.

fluxglass formerstiffens the melt (alumina)Contributes: CaO · K₂O · Na₂O · Al₂O₃ · SiO₂

In published recipes

Used in 330 of 10,859 glaze recipes (3.0%)

Typical amount when present

37.3% of the dry batch — half of recipes fall between 20.1% and 50%.

Fired surface of those recipes

Glossy 49% · Matte 27% · Semi-glossy 13% · Satin matte 11%

Cones where it appears

Share of recipes containing this material that fire to each cone.

Most often mixed with

Materials that appear in the same recipes most often.

Whiting73%Silica48%EPK45%Red iron oxide34%Zinc oxide26%Dolomite26%Bentonite25%Gerstley borate18%

Chemistry

Raw formula: 0.304CaO·0.340Na₂O·0.356K₂O·1.075Al₂O₃·8.10SiO₂
Molecular weight: 667
Fired formula: same as raw
Equivalent weight: 667
: variable material — get an analysis of your sample

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

A variable material with a wide melting range depending on the sample, and it may contain fluorine (the de-fluorinated grade is D.F. stone). Hamer notes lower surface tension in the melt than feldspar, so it is sometimes used in place of spar to fight crawling.

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 Cornwall stone do potters use in a glaze?: Across 330 published glaze recipes containing it, the typical amount is 37.3% of the dry batch, with half of recipes between 20.1% and 50%. 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 Cornwall stone used at?: It appears in recipes across the range; the most common cones among published recipes are cone 10, cone 6, cone 9. Where a material sits depends on the rest of the recipe more than on the material itself.
Is Cornwall stone 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.

Related materials

Glaze material	recipes	typical
Custer feldspar	2,210	37.5%
Potash feldspar	1,446	36%

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.

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