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

Copper, Iron, and Rutile Line Blends

        These line blends show the effects of Copper Carb, Iron Oxide, and Rutile on the Permafrost base as well as the effects of Copper Carb on the Shorn Base. The increments of each line blend consisted of 1% - 5% regardless of colorant or base glaze. 

                   Permafrost Base                                         Shorn Base

                       Neph Sye - 45                                       Wollastonite - 25

                           Flint - 30                                            Spodumene - 25

                         Whiting - 8                                        Cornwall Stone - 25

                       Dolomite - 10                                            Talc - 25

                           Talc - 7

Permafrost Base, Copper Carb Line Blend

      Copper Carb does not flux the Permafrost Base to a noticeable amount, however increased amounts of Copper Carb begin to form very small crystals that sparkle on the satin glaze surface.

Permafrost Base, Red Iron Oxide Line Blend

      The Permafrost Base becomes more and more runny and glossy as higher amounts of fluxing agents are added, such as Red Iron Oxide. The two tiles furthest to the right were so fluid that they ran off the tile.

Permafrost Base, Rutile Line Blend

         Rutile, like Red Iron Oxide, fluxes the Permafrost Base in higher amounts. At 3% the Rutile begins to noticeably crystalize on the surface of the glaze. By 5% it fluxes the glaze enough to add a Hare's Fur like effect.

Shorn Base, Copper Carb Line Blend

     The Shorn Base alone is very runnny, so the effect of any fluxing that the Copper Carb might have caused is not noticeable. Increased amounts do, however, change both the color of the crystals and the glaze matrix. Higher amounts of Copper Carb deepen the teal background and make the crystals gunmetal.