This is Polar Ice casting, a cone 6 translucent porcelain that uses New Zealand Halloysite. 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. This 1% addition can be refined. A program of testing could indicate that a lower percentage of Veegum could work, increasing the casting rate. The polar ice information page has very good information, under the heading “Casting Recipe” (it deals with the trade-offs of using this kaolin in casting bodies).
| Troubles |
Casting Slip Problems
Casting slips are deflocculated in order to reduce water content. It is important to understand this phenomenon and know how to assess a slurry to know what it needs. |
| Glossary |
Casting Rate
Casting rate describes how quickly a layer of clay builds against the mold surface during slip casting and how quickly items release from molds and can be handled. |
| 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 |
| 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. |
| 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. |
| Materials |
New Zealand Halloysite
The whitest burning kaolin available to potters. Low plasticity. Very sticky when wet, suspends glazes well. |
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