Help with crazing and underglaze flaw

[Odieartist]

Hi Everyone,

I am having two different problems. First I am encountering crazing about a month after I take pieces out of the kiln. The second problem I am encountering on other pieces is that painted designs become bump after they are glazed. The glaze and the paint are both Duncan brand. Please help.

[Bill Kielb]

The crazing is most likely due to enough of a coefficient of expansion difference between your glaze and Claybody.. That it is delayed indicates they are likely close but enough of a mismatch that it eventually crazes. Lots of ways to try to fix crazing so I expect you will have lots of questions to answer. As always pictures here help folks a lot in being able to respond.

The underglaze and glaze issue often is the result of heavy underglaze application and certain colors of it being a bit more refractory than the overglaze will melt.

As long as the underglaze is not fired beyond its range we have had success using our own mixed clear glaze with a bit more boron added to melt over some of the tougher colors. This may or may not be something you want to pursue.

If what I described is your issue, I would ask if you have less problems over watercolor (thin) type applications and whether there are any particular colors that are worse than others with the bubbling.