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Sheryl Leigh

How do you store your own mixed clay?

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4 hours ago, Mark C. said:

When rehydrating clay you will find all stonewares  do this very easy. Porcelains on the other hand do this very poorly and take forever.

A very distinct lesson of the differences in clay chemistry between two clay bodies. Ball clay (2:1 particles) have inner layers that act like micro sponges, absorbing (rehydrating) more rapidly. Porcelain being primarily kaolin (1:1 particle) has no inner layer, only surface area. ( think saltine cracker in appearance). Which means all the particles must be directly exposed to moisture in order to rehydrate.

At best, you could drill holes in a porcelain block about two inches apart; to allow water more direct contact. Otherwise you need to break up the block into small chunks; submersed in water and drain off excess the next morning to completely hydrate. Either way, the usual dust hazard precautions apply. If your porcelain body uses Nep Sy as the primary body flux: every time you reclaim/ rehydrate the texture will become more granular and less plastic. The nature of soluble salt fluxes: crystalline nodules will form.

Edited by glazenerd
Verb confusion

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I'm making the assumption that Nep Sy is only used in cone 6 or lower bodies as a flux?-I was not aware its used in high temp clay bodies due to it melting point?

I never have had experience in cone 6 porcelains

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Mark:

30 years ago, most stoneware/ porcelain bodies used Custer or g-200. (Cone 6-10) mid to late 90's it switched to minspar, Kona, or g-200hp because Custer became unstable. Bodies started switching to Nep Sy ten years ago, and more so in the last five. Potassium spars run roughly 2-3 times  that of sodium. Then add the fact that freight costs can run more per lb. than the actual materials. 

Both potassium and sodium are spent by 2190F, so melt temperature is not really a concern for either cone 6-10. Cone 10 just makes a downward adjustment in molar flux levels, which can be coupled with adjustments in silica to offset glass formation produced from the extended heat work. 

 

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Out west here 30 years ago a lot of clays used Kingman Feldspar before the mine closed down-then switched to Custer after that. (just keeping the record straight)

I used just such a body then from the only filter pressed body then and now on the west coast Quyle kilns. They used Kingman for many decades after the mine shut as that like me bought a large supply. I still use Kingman in most glazes when a potash feldspar is called for.In 1982 I drove to Kingman and bought 30- 100 # bags. They now are a bear to move but back in the day many materials came in 100# bags.When I was buff they where light as a feather now they are a two man bag.

Back then this feldspar came to Westwood clay company(now Laguna) in rail cars and freight costs where very low.

http://www.quylekilns.com/about_us

Edited by Mark C.

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Mark:

proximity to local sources play a very large role in raw material selections these days. Yet another reason I think Nep Sy is becoming the body flux of choice: it is mined coast to coast and in Canada. Potassium sources have all but dried up, more and more is being imported. Just as I have been seeing changes in raw clay sources. Updated analysis sheets are different, Tony Hansen needs to update several of his. Just as some ball clay are changing. No different than Custer, after digging through a mine for 20 plus years: particle sizes change as does the chemical makeup. Which is my thought on recent threads about moisture content- wet clay. Chemical changes would alter the CEC, which in turn changes retained moisture content: which in turn changes plasticity.  Just a hunch..

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