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Cone 04 Slip Casting recipe - Ceramics Monthly - Summer 1981

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Don't know if anyone remembers when CM featured recipes for "flameware" bodies but here's one from that period. 

From Bruce Kremer, a grad student at Alfred

Porous Flameware Body

Petalite                      25

Spodumene             25   

Kaolin                         25

Tennessee Ball      25

Darvan                       .7

If anyone tries mixing this recipe please post your experience. No idea what "petalite" is, or how it acts in a slip body, but I'm certainly curious?



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26 minutes ago, Jeff Longtin said:

If anyone tries mixing this recipe please post your experience. No idea what "petalite" is, or how it acts in a slip body, but I'm certainly curious?

Petalite is a lithium aluminum silicate mineral (more simply a lithium feldspar) that is commonly used in clay bodies. It is valuable because it provides an insoluble source of lithium and has the highest Li2O:Al2O3 ratio of any natural mineral. Lithium is a strong alkaline flux and is effective over all temperature ranges. It imparts lower expansion and gives a unique color response to copper and cobalt in glazes. Some commercial versions have a chemistry that fairly closely matches the theoretical chemistry given here.

Petalite is most prized for its mineralogical properties. It is especially valuable in imparting thermal shock resistance to clay bodies because it has almost zero expansion when heated above 700C. Bodies with 60%+ petalite can take a direct flame and rapid water cooling without failure. To make a plastic clay body mix petalite with as much ball clay as needed. For a casting body, use as much kaolin as needed to achieve the desired casting properties. Bentonite can be added to either type of body to increase the petalite proportion.

One serious problem with low expansion petalite bodies is that it is very difficult to achieve glaze fit. All common glazes will craze. This is compounded at lower temperatures where the limited low-expansion silica and alumina necessary for melting raises glaze expansion. For some low-expansion bodies, it is almost impossible to match a glaze

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I'm using petalite in my liner glaze*, which was a study in craze control.
Spodumene has more lithium per unit weight, but petalite was more competitive in lithium per unit co$t, with side benefit of avoiding the reported foaming/rinsing.

*was, on account of petalite costs have gone up so much!
I'll be re-visiting my liner glaze formula soon, very ...I have enough petalite to last a year or two.

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