Badly crawled glaze fired at cone 5 reduction

It was spray applied on the dried bowl (no bisque fire) an was too thick (not to mention under fired). But the main problem was a glaze recipe having too high a clay content. If a glaze has more than about 25% clay, consider a mix of the raw clay and calcined. For example, you can buy calcined kaolin to mix with raw kaolin. Or you can calcine the clay in bowls in your kiln by firing it to about 1200F.

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Glossary	Calcination Calcining is simply firing a ceramic material to create a powder of new physical properties. Often it is done to kill the plasticity or burn away the hydrates, carbonates, sulfates of a clay or refractory material.
Materials	Calcined Kaolin This is kaolin powder that has been fired in a furnace to remove the 12% crystal water and render it non-plastic.
Troubles	Crawling Ask yourself the right questions to figure out the real cause of a glaze crawling issue. Deal with the problem, not the symptoms.

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