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This is Polar Ice casting, a New Zealand Halloysite based cone 6 translucent porcelain. The base body recipe would never have enough plastic strength to pull itself from this mold without tearing. But the addition of 1% Veegum gives it amazing strength. This dried cast bowl measures 130mm in diameter and 85mm deep, it only weighs 89 gm! The slip was in the mold for only 1 minute before pour-out. Of course, there is a price to pay for adding the Veegum: Increased casting time and more difficult deflocculation. Regular bentonite can be used in most bodies, but for super-whites like this, Veegum (or equivalent) is the choice. Testing is needed to determine what percentage gives the needed strength yet does not increase the casting time too much. The polar ice information page at plainsmanclays.com has very good information, under the heading “Casting Recipe”, about the challenges and trade-offs of using this kaolin in casting bodies.
Articles |
Formulating a Porcelain
The principles behind formulating a porcelain are quite simple. You just need to know the purpose of each material, a starting recipe and a testing regimen. |
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Glossary |
Slip Casting
A method of forming ceramics. A deflocculated (low water content) slurry is poured into absorbent plaster molds. As it sits in the mold, usually 10+ minutes, a layer builds against the mold walls. When thick enough the mold is drained. |
Glossary |
Deflocculation
Deflocculation is the magic behind the ceramic casting process, it enables slurries having impossibly low water contents and ware having amazingly low drying shrinkage |
Materials |
New Zealand Halloysite
The whitest burning kaolin we have ever seen. It is very sticky when wet, suspends glazes well & makes super white porcelain (with help from a white bentonite). |
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