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Help With Shivering

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I need help!!! I teach at an elemtery school and 2 pieces have shivered after comming out of the kiln. I have never had a problem with this untill now and I don't know why. Both pieces were in seperate kilns.

 

I use a high talc body (Steve's white from AArdvarks)

Electric kiln (oxidation)

^04 Bisque

Mayco underglaze

Sometimes I fire the underglaze to 06 to set it, and sometimes I go straight to the overglaze.

Mayco clear overglaze

^06

 

Is it possible that not fireing the underglaze first is the culprit? Do I really need to fire the underglaze to ^06 to set it come to that? I'm worried that in 10 years all their 1st grade projects will have shivered off all their glaze. Can anyone help?

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Hello, i think the problem is glaze fit matter (glaze and body). Shivering is the reverse of crazing, so the remedies are the opposite of prescriptions for crazing. You must increase the high expansion oxides in the glaze, so it will contract more when it is cooling. High expansion oxides are feldspar and quartz/flint. Or you can decrease a flint content in clay (body). :rolleyes:

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Hello, i think the problem is glaze fit matter (glaze and body). Shivering is the reverse of crazing, so the remedies are the opposite of prescriptions for crazing. You must increase the high expansion oxides in the glaze, so it will contract more when it is cooling. High expansion oxides are feldspar and quartz/flint. Or you can decrease a flint content in clay (body). :rolleyes:

 

Thanks for the reply! would it be possible to simply add feldspar/flint to a commercial glaze? I would do tests of course. Thanks again.

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Yap, it's correct. You may take this way. First add begins 5, 10, 15, 20%, and see what happen for each recipe. I also suspicious to your clay body. May be you can try another type of clay body. May be the vitrification of both different too far.

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Yap, it's correct. You may take this way. First add begins 5, 10, 15, 20%, and see what happen for each recipe. I also suspicious to your clay body. May be you can try another type of clay body. May be the vitrification of both different too far.

 

Thanks so much. I'll give it a try. I'm not sure if I'll be able to actually see the results, because it has only happened to 2 out of hundreds of pieces. But maybe adding 5% -10%, if it's not to runny, is just a good thing to do. Thanks again, you have really helped alot!!!

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