Natania Posted July 10, 2014 Report Share Posted July 10, 2014 When refiring some plates with a regular glaze load the plates cracked (in half) while the rest of the load was fine. I suspect thermal shock. When refiring does one need to heat up much slower with ware that has been previously vitrified? Link to comment Share on other sites More sharing options...
Natania Posted July 10, 2014 Author Report Share Posted July 10, 2014 Sorry for the double post. Stupid cell phone Link to comment Share on other sites More sharing options...
Pres Posted July 10, 2014 Report Share Posted July 10, 2014 Fixed the double post. Answer to your question-When firing a mixed glaze load of ware that has been vitrified in full glaze fire with work that has not do you have to change your firing schedule? In my humble opinion the answer is no you do not have to change your firing schedule. Your kiln may have cooled too fast causing the plate cracking. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted July 10, 2014 Report Share Posted July 10, 2014 without knowing what your schedule was, my first inclination would be thermal shock and too fast. But Pres also mentions cooling too fast. Refires can be tricky. If it were cooling too fast why would just the retires be cracked? Marcia Link to comment Share on other sites More sharing options...
Guest JBaymore Posted July 10, 2014 Report Share Posted July 10, 2014 Plates are flat objects sitting on THICK thermal masses called kiln shelves. When the kiln is heated up, the exposed thin plate rims will heat pretty quickly and evenly. But because of the thermal mass of the plate bottom and the kiln shelf, the poor circulation with kiln atmosphere on the back side of the plate, and the fact that radiant heat transfer (particularly if this is an electric kiln) is not typically hitting even the plates top surface well......... it can cause the plates (and low wide bowls) to crack. Rim expands... bottom does not at the same time. Almost the same effect happens in reverse if ther kiln is cooled too quickly due to the cooling retarding of the thermal mass of the plate bottom on the kiln shelf. Rim contractss... bottom does not at the same time. best, ......................john Link to comment Share on other sites More sharing options...
Benzine Posted July 10, 2014 Report Share Posted July 10, 2014 John, Would raising the plates do anything to solve the issue; through the use of coils under the plates, or the commercially made plate setters that are available for purchase? Link to comment Share on other sites More sharing options...
Bob Coyle Posted July 10, 2014 Report Share Posted July 10, 2014 I extrude little 1/4 inch rods and fire them in my next firing. I then break off little 1 inch or so pieces and set them under any flat or thick pieces. They can be used over and over and are a lot cheaper than stilts. Better safe than sorry. Link to comment Share on other sites More sharing options...
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