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karinagenevieve

Trouble Glazing Locally Harvested Clay

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Hello! I have been harvesting a beautiful blue marbled clay, processing it, and then making cups. I did a test-bisque at cone 04 which turned out great, but the low-fire glaze that I applied afterward (cone 05-06 glaze) did not absorb easily and took several hours to dry. Is it worth trying to fire it anyways? And in the future: Will I run into complications if I bisque at a lower temperature (cone 05-08?) then apply glaze and fire at 05? The glaze directions say to bisque at cone 04, but I'm assuming its not necessary if the clay I'm working with is extremely low-fire? Thanks for the help! I am a beginner ceramicist working at home with access to a community kiln. I have never worked with locally harvested clay before and its amazing but difficult to figure it all out. 

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local clay can be a slow curve learning to work with it ( throwing ,hand building ,firing, glazing etc. ) lots of testing needed. usually it easier to add materials to it to get it to work and fire better.

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I did a test-bisque at cone 04 which turned out great, but the low-fire glaze that I applied afterward (cone 05-06 glaze) did not absorb easily and took several hours to dry.

A sure sign that this natural clay had begun to vitrify at this low temperature. Which would mean it has a higher than normal amount of potassium/sodium/calcium and magnesium. OR it has a very high carbon content, and the sodium sulfate gases it is emitting is sealing the surface, making it hard.

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I agree with Mark's answer, but in regards to your next steps:

 

>Is it worth trying to fire it anyways?

 

Absolutely. At this point it is a test piece and whatever happens when you glaze fire it will teach you something about your clay.

 

 

>Will I run into complications if I bisque at a lower temperature (cone 05-08?) then apply glaze and fire at 05?

 

No one can say for sure, except for you after you try it. But this is the logical next thing to try.

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