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Refiring Question


Natania

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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?

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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.

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Guest JBaymore

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

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