Wood Ash (average of six)
A standard material in Glazecalc's library: its oxide analysis, unity contribution and hazards.
What it is
- Kind
- Fluxes
- Status
- Historical
- Formula
- CaO 37%, MgO 11%, K₂O 16%, Na₂O 1%, P₂O₅ 9%, SiO₂ 7%, Fe₂O₃ 1%, MnO 2%, LOI 16%
- Also called
- Wood ash, 木灰
- Similar materials
- Synthetic Wood Ash (合成土灰)
- Source
- Digitalfire Reference Library: Wood Ash (an average of 6 wood ash types) (2026-11-04)
Historical: potters burnt their own wood and either washed the ash in water, pouring off the charcoal that floats, or sieved it dry, which keeps the soluble potash and soda. This is Digitalfire's average of six wood ashes, not one ash: real ash differs from wood to wood and from batch to batch, so test your own, for example in a line blend with feldspar.
Oxide analysis and unity formula
Glazecalc has the analysis of Wood Ash (average of six) as weight percent of the raw material. The unity contribution is the moles of each oxide in the amount of Wood Ash (average of six) that holds 1.0 mole of flux, which is how Glazecalc adds it into a recipe's unity formula.
| Oxide | Weight % | Unity contribution |
|---|---|---|
| CaO | 37 | 0.575 |
| MgO | 11 | 0.238 |
| K₂O | 16 | 0.148 |
| Na₂O | 1 | 0.014 |
| P₂O₅ | 9 | 0.055 |
| SiO₂ | 7 | 0.102 |
| Fe₂O₃ | 1 | 0.005 |
| MnO | 2 | 0.025 |
- Equivalent weight
- 87.19
- Fired weight
- 73.24
- Loss on ignition
- 16%
The equivalent weight is the grams of Wood Ash (average of six) that hold 1.0 mole of flux. The fired weight is what is left of that after firing.
Hazards and safety
Hazards: Wood ash is caustic, and so is the water it is washed in: wear gloves and eye protection, and avoid breathing the dust.
Use it in a recipe
Add Wood Ash (average of six) to a recipe in the Glazecalc calculator to see what it does to a glaze's unity formula.