Material Information: Wollastonite

The acicular nature of Wollastonite's crystals

50/50 Base
Neph Sye - 50
Wollastonite - 50

50/50 Base + Copper
Neph Sye - 50
Wollastonite - 50
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Copper Carb - 2% 

Shorn Base + Copper
Wollastonite - 25
Spodumene - 25
Cornwall Stone - 25
Talc - 25
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Copper Carb - 4%

Shorn Base + Cobalt
Wollastonite - 25
Spodumene - 25
Cornwall Stone - 25
Talc - 25
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Cobalt Carb - 2%
Copper Carb - 1%

     Wollastonite is a natural mineral made of Silica and Calcium (CaSiO3) that is acicular - meaning that the crystals that make up Wollastonite are needle like (above). Because of this unique structure and chemical makeup there are a few things that Wollastonite can do that are quite interesting:
     1. The crystaline structure of Wollastonite can produce visible crystals in a fired glaze, seen in the Shorn glazes (below right), when the base glaze is low in alumina - the higher alumina will stiffen the glaze melt in such a way that the crystals cannot form
     2. The crystaline structure of Wollastonite holds onto itself allowing the dry material to be lifted fingers down, in the same way that straw can be lifted fingers down
     3. The fibrous form of Wollstonite is a good additive in low fire clay bodies because it promotes low thermal expansion and reduces drying and firing shrinkage
     4. Wollastonite is an excellent source of Calcium - a strong flux - for glazes that does not bubble during the firing due to off gassing whereas Whiting, the other prominent source of CaO, produces bubbles in the glaze from off gassing