Amakusa Pottery Stone (天草陶石)
A standard material in Glazecalc's library: its oxide analysis, unity contribution and hazards.
What it is
- Kind
- Feldspars and stones
- Formula
- SiO₂ 78.64%, Al₂O₃ 15.1%, Fe₂O₃ 0.36%, TiO₂ 0.02%, MgO 0.24%, Na₂O 0.21%, K₂O 2.77%, LOI 2.79%
- Also called
- 天草陶石, Amakusa stone, Amakusa toseki
- Sold in
- JP
- Source
- 佐賀県陶磁器原料株式会社 (Arita): 釉薬原料の化学分析表, the supplier's typical analysis of what it sells (undated; read 2026-10-19)
A typical analysis from one supplier in Arita: check it against your own supplier's. Amakusa stone is graded by its iron, from 特等 (the least) to 四等, and the low-iron grades are now scarce, so grades differ. It is a rock of quartz and sericite with about 3% alkali, not a feldspar and not Cornwall stone: do not swap it for either.
Oxide analysis and unity formula
Glazecalc has the analysis of Amakusa Pottery Stone (天草陶石) as weight percent of the raw material. The unity contribution is the moles of each oxide in the amount of Amakusa Pottery Stone (天草陶石) that holds 1.0 mole of flux, which is how Glazecalc adds it into a recipe's unity formula.
| Oxide | Weight % | Unity contribution |
|---|---|---|
| SiO₂ | 78.64 | 33.777 |
| Al₂O₃ | 15.1 | 3.822 |
| Fe₂O₃ | 0.36 | 0.058 |
| TiO₂ | 0.02 | 0.006 |
| MgO | 0.24 | 0.154 |
| Na₂O | 0.21 | 0.087 |
| K₂O | 2.77 | 0.759 |
- Equivalent weight
- 2580.64
- Fired weight
- 2508.64
- Loss on ignition
- 2.79%
The equivalent weight is the grams of Amakusa Pottery Stone (天草陶石) that hold 1.0 mole of flux. The fired weight is what is left of that after firing.
Hazards and safety
Hazards: Contains crystalline silica; avoid breathing the dust.
Use it in a recipe
Add Amakusa Pottery Stone (天草陶石) to a recipe in the Glazecalc calculator to see what it does to a glaze's unity formula.