nellhazinski

I want to thank everyone for their responses. Very helpful. I actually have the Hamer book and the section on cracks is great. Years ago,I used the formula "Rhodes" celadon for my blue celadon glaze. This glaze has a lot of Cornwall stone, which I thought may be the problem. It started to craze in the manner I described, so I increased the silica, but the problem persisted. I was frustrated and chose to test other celadons, and found another beautiful one, which is the one I am now struggling with. This may be a silly question, but does the addition of bentonite lower the COE of the glaze? This glaze sinks to the bottom almost immediately when mixed, so I've been adding perhaps too much bentonite. I'll be researching on Digitalfire per Hulk's links. Thanks so much for these.

Thanks for the info. Looks like I have some work to do. The glaze is cracking, not the clay.

interested in this, but what is a thermal COE? I've thought that the glaze thickness might be the issue, but in some cases the glaze does not appear to be too thick.

I have a problem with irregular cracks forming on some of my fired porcelain bowls and plates. The bowls are fired to cone 10 and the cracks usually appear months after firing. The bowls, glazed in celadon have a footed flat bottom and are also glazed on the under surface inside the foot. Does anyone have ideas about the cause of the cracks? the first image is a drawn example of the crack; the 2nd is an actual crack on a bowl.