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The EP kaolin has been mixed 70:30 with nepheline syenite. This creates a body that matures below cone 6. And it enables comparing the degree to which the two kaolins influence vitrification (and their contribution to fired color in a vitreous body). The darker one is more plastic, has higher drying shrinkage more soluble salts. These dry test bars were fired at cone 4-8 and had similar fired shrinkages and porosities. However, the one on the right fired whiter at all temperatures. These differences would impact the plasticity and drying shrinkage of bodies containing a significant percentage of the material. They would also influence the ability of this kaolin to suspend slurries.

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In ceramics, EPK, or EP Kaolin, is used in clay bodies and glazes. EPK feels fairly plastic on wedging. But it splits like this during throwing (top right). It needs the help of bentonite or ball clay to be usable in porcelain or stoneware bodies. Tile #6 kaolin is thus a much better choice for plasticity (although higher in iron and titania).
But EPK shines in glazes. A slurry of pure EPK (bottom), mixed to only 1.15 specific gravity, holds this spatula upright! Glazes employing as little as 20% EPK, without added electrolytes, are naturally thixotropic. And its sticky nature helps with adherence and dry hardness. Consider the engobe employing it (top left). It gels and clings to this rubber spatula in an even layer, with no drips. If leather-hard ware is carefully dipped and extracted, it stays put (even if it takes hours to dry). The performance of EPK suspending glazes for use on bisque is even better.
Are there other sticky kaolins that gel? Yes. Grolleg and New Zealand kaolin. What if you cannot get either? Tile #6 is a good choice because it dries hard. But, it may need the help of Epsom Salts to produce a slurry having thixotropy like EPK.
| Materials |
EP Kaolin
A kaolin that gels slurries (thus handy to suspend ceramic glazes). It is plastic and fires white enough that it is also valuable in porcelain bodies. |
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