An example of how a glaze that contains too much plastic clay has been applied too thick. It shrinks and cracks during drying and is guaranteed to crawl. This is raw Alberta Slip. To solve this problem you need to tune a mix of raw and calcine material. Enough raw is needed to suspend the slurry and dry it to a hard surface, but enough calcine is needed to keep the shrinkage low enough that this cracking does not happen. The Alberta Slip website has a page about how to do the calcining.
|Media||Subsitute Gerstley Borate in Floating Blue Using Desktop Insight|
Raw ceramic glazes contain clay to harden them on drying and to suspend the slurry. The more clay there is the more the glaze shrinks as it dries on the piece.
A ceramic glaze fault that occurs during firing of the ware, islands of glaze form as it crawls, leaving bare patches of body.
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.
Many ceramic glaze appearance issues are related to the thickness with which the glaze is applied. Many glazes are very sensitive to thickness, so control is needed.
|Materials||Alberta Slip 1900F Calcined|
Powdering, Cracking and Settling Glazes
Powdering and dusting glazes are difficult and a dust hazard. Shrinking and cracking glazes fall off and crawl. The cause is the wrong amount or type of clay.