|Monthly Tech-Tip |
This is G2415J Alberta Slip glaze on porcelain at cone 6. Why did the one on the right crawl? Left: thinnest application. Middle: thicker. Right thicker yet and crawling. All of these use a 50:50 calcine:raw mix of Alberta Slip in the recipe. While that appears fine for the two on the left, more calcine is needed to reduce shrinkage for the glaze on the right (perhaps 60:40 calcine:raw). This is a good demonstration of the need to adjust raw clay content for any glaze that tends to crack on drying. Albertaslip.com and Ravenscrag.com both have pages about how to calcine and calculate how much to use to tune the recipe to be perfect.
Alberta Slip 1900F Calcined
A ceramic glaze fault that occurs during firing of the ware, the molten glaze pulls itself into islands leaving bare patches of body between.
Many ceramic glaze benefits and issues are closely related to the thickness with which the glaze is applied. Many glazes are very sensitive to thickness, so control is needed.
Ask yourself the right questions to figure out the real cause of a glaze crawling issue. Deal with the problem, not the symptoms.