Plainsman Clays | WOLL
Wollastonite
Wollastonite is calcium silicate, with crystals that form fine needles instead of grains. It adds calcium and silica to a recipe together, and almost none of its weight leaves as gas.
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Wollastonite is used in a glaze as a source of calcium, commonly between a tenth and a quarter of the recipe, and in a body at a few parts in a hundred. Almost none of its weight leaves as gas during the firing, so very little gas passes through the glaze while it seals over. It supplies silica as well as calcium, so a recipe that takes its calcium from wollastonite needs less silica added separately. The two do not swap by equal weight, so the recipe totals have to be recalculated. In a body the needles reduce shrinkage through drying and firing and make the fired ware more resistant to cracking, though they do not add dry strength.
- Calcium silicate, with crystals that form fine needles
- Adds calcium and silica together, with almost no weight lost as gas
- A tenth to a quarter of a glaze, a few parts in a hundred of a body
- In a body the needles toughen the fired ware and reduce shrinkage
