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GEP

Kyanite And Functional Ware

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GEP    863

I asked this question inside another sort-of related thread already, then decided it really was a new topic:

 

I've often heard of adding kyanite to clay bodies to add thermal shock resistance to raku and pit fired pots. Has anyone tried adding kyanite to a clay body when firing cone 10 functional pots? My students and I are getting ready for a cone 10+ wood-firing in the fall. Some extra thermal shock properties would be helpful, especially for those who want to make thinner-walled pots. 

 

I've seen cone 6 and cone 10 clay bodies that contain kyanite "for strength" however they all seem to have fairly high absorption rates, higher than I would want to use for food ware.

 

If anyone has any experience with this, or if you have information about how much kyanite be used (even if the answer is "none"), please share!

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Wyndham    98

I would think wedging some Kaynite/mulite into a smooth, grog free, clay body would help, maybe 3-5 %.

The alternative might be to use a more robust clay body and cover it with a white slip after trimming  for a smooth surface. This would help if you want flashing slip look to some work.

 

I don't think you would have too much thermal shock on the way up if the pieces are dry. The problem can occur on the cool down if it's too fast, such as a fiber wood fire kiln.

I've seen this happen in a wood fired salt kiln but I think it is due to glaze compression from heavy salt coating.

Wyndham

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OffCenter    82

I don't think you need to do anything to the clay to make it more resistant to thermal shock in a wood firing. I've had pots thick and thin stand up to the flame on one side without ever using anything for thermal shock. I've made "soldier pots" (pots that you're willing to sacrifice for pots behind them) that were blasted by the main direct flame and while they got too much kiln snot on them they survived. It is often used not to protect against thermal shock during the firing but to make the finished pot able to withstand the thermal shock of the oven or even the stove top. You may also want to consider that it is probably going to show up on the unglazed part of the finished pot as gray specks which you may not like on light or dark clay. But, maybe there are different kinds now. It has been a long time since I made flameware.

 

Jim

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OffCenter    82

"Kiln Snot" Jim?

 

Pots up front near (or in) the firebox really get blasted with wood ash forming a glaze that is thick and gray. When it's on shelves a lot of potters call it "kiln snot" when it's on pots some people like it and call it glaze. I don't like it. Don't get me wrong. I love the nice ash glazing and flashing that goes on further back in the kiln. There the glaze is like amber.

 

Jim

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