Cracking glaze

[Cassie___]

Hello folks, I bought some bisque earthen ware from Bisque Direct to decorate in my local pottery class. The supplied glaze unfortunately has mostly cracked on firing, some mud cracking but largely circular cracks indicating the glaze is contracting more than the earthen wear. However in the areas where it has been thinly applied it seems to have survived. I spent many hours decorating the plates. Is there anyway to remedy the situation? Thanks

[Callie Beller Diesel]

Hi and welcome to the forum!

I wish I had better news, especially for your first post. A cracking or crazing glaze is indeed a sign of it not fitting properly. If you were to do an ice bath/boiling water shock test, you’d probably find that even the areas that aren’t crazed will do so. The cracks may appear over time even if you don’t.

Check with your instructor and ask if this is common, or if they’ve done those shock tests to bring out any possible delayed crazing tendencies. If it’s typical, you m’ll have to use a different clear. Doing some test samples to find one that works before committing to more precious work will save you some heartache. The good news is, now that you have practice painting the first set, the second time around will be better.

If the instructor says it isn’t typical for these materials, occasionally with earthenware you do see a glaze firing that didn’t get quite hot enough to properly mature the clay body. That can can cause a clay/glaze combo that normally works to craze. Refiring might fix it in that one instance, but it’s the exception to the rule. 

[Cassie___]

Thanks that's very helpful to know it might not have been hot enough. I will have to check through that with them.