• Materials for Ceramics

Alberta Slip 1000F Roasted

Alternate Names: Roasted Alberta Slip

Notes

Fully calcined Alberta Slip (fired at 1900F) has an LOI of 9%. However it is not necessary to fire it that high to remove the plasticity (to reduce shrinkage during drying). The albertaslip.com website outlines this 1000F roasting process. This version looses only 3% of its weight on firing, so the analysis totals 97.

Related Information

Roasting Alberta and Ravenscrag Slips at 1000F: Essential for good glazes

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Roasted Alberta Slip (right) and raw powder (left). These are thin-walled 5 inch cast bowls, each holds about 1 kg. I hold the kiln at 1000F for 30 minutes. Why do this? Because Alberta Slip is a clay, it shrinks on drying (if used raw the GA6-B and similar recipes will crack as they dry and then crawl during firing). Roasting eliminates that. Calcining to 1850F sinters some particles together (creating a gritty material) while roasting to 1000F produces a smooth, fluffy powder. Technically, Alberta Slip losses 3% of its weight on roasting so I should use 3% less than a recipe calls for. But I often just swap them gram-for-gram.

Will this crawl when fired? For sure!

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This high-Alberta-Slip glaze is shrinking too much on drying. Thus it is going to crawl during firing. This common issue happens because there is too much plastic clay in the glaze recipe (common with slip glazes). Clay is needed to suspend the other particles, but too much causes the excessive shrinkage. The easiest way to fix this is to use a mix of raw and roasted Alberta Slip. The roasted Alberta Slip has no plasticity and thus much less shrinkage (but it still has the same chemistry). Many matte glazes have high kaolin contents and recipes will often contain both raw and calcined kaolin for the same reason.

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