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Is There A Way To Distinguish Low-Fire From High-Fire Clay Piece?


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This didn't happen to me, but got me to thinking and looking for an answer.  A potter friend found an old piece she made a long time ago and bisque fired but never glazed.  Now shes not sure if it's low fire or high fire.  I can't imagine a way to figure this out but thought I'd ask if anyone out there knows.  At any rate, it would be okay to apply low fire glazes and fire appropriately, correct?

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It's porosity maybe give you a clue.  Low fire clay is bisqued closer to its vitrification point, than a mid to high fire clay is.  So if it seems relatively absorbent, then it might be a mid to high fire clay.

 

Also, color can be a clue, in some cases.  Many stoneware clays have a pinkish color, after the bisque.  If it's a white clay body, it will be tough to tell.

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I suggest you do not high fire it now no matter what. I have seen this mistake many times and it always turns out worse than yoiu you think.

You could put the whole piece into a larger bisqued high fire bowl and then fire to cone 10 and when it melts its all contained in the bowl.

Thats the only way to avoid a disaster.If you low fire a high fire clay it can leak if its a funtional piece-if its sculpural-no harm.

If she does not care about vitrifcation then low fire it also with no harm.

My motto on this is when in doubt throw it out-but thats just my 2 cents if you are thinking high fire.

I had a rule about low fire in my high fire studio-I would not store it inside-I had a bag outside for about 10 years -thenone day I had a pice melt and run in my high fire kiln-I will not say who threw this into the load and with a spotty memory it may have been me, but now my rule is no low fire on the property.

Mark

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You could put the whole piece into a larger bisqued high fire bowl and then fire to cone 10 and when it melts its all contained in the bowl.

Thats the only way to avoid a disaster

Like Mark says...  Long ago I thought it would be neat to paint pictures on the surface of some commercial tiles I bought. They looked like high fire to me, besides I was just firing to cone 6... what could go wrong.

 

Well when I opened the kiln, there were no more tiles, only blobs firmly melted into the kiln shelf. Betcha I don't do that again.

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