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Struggles Developing Clay Body From Local Clay

clay body formulation local clay clay/glaze interaction

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#21 Biglou13

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Posted 15 March 2014 - 07:53 PM

Have you tested vitrification/ absorption of fired un glaze piece?

The leaking possibly leans towards under vitrified body.

It could be other things.

Did you try same body with more spar, or replacing some if not all with nephsy.

Do you have some gold art it tends to pull a lot of "unknowns", finicky bodies togehter.

BIG congrats on slugging it out this far!!!!
It looks super good and promising.
Let me know if you need help testing for vitrification/absorption. Which I think should be your next in process.

Welcome to the "I made my own clay" club.
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#22 Rockhopper

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Posted 15 March 2014 - 09:46 PM

Have you tested vitrification/ absorption of fired un glaze piece?

The leaking possibly leans towards under vitrified body.

It could be other things.

Did you try same body with more spar, or replacing some if not all with nephsy.

 

 

My testing method so-far has been to mix small batches, and make two arch-shaped tiles from each.  Both tiles are bisqued at ^04, then fired at ^6 - one glazed & one un-glazed.  Have tested absorption (24hr soak + 2hr boil) on all un-glazed tiles that survived ^6 firing. 

 

My scale only weighs in whole grams, so not real precise on the relatively small tiles (35g dry) - but the previous batch, using 10% spar, showed the same weight after soak + boil as they did dry, indicating they absorbed less than 1g  ( < 2.8 % ).  I backed the spar off a bit for this batch, because the previous tiles had a bit of sheen to them, and I was afraid they might still be a bit over-fired.  This batch, with 8.5% spar, absorbed around 7% :(  so.. it looks I'll go back to 10% with the next batch.

 

Interesting you mention Gold-Art.  I did some tests a while back adding various combinations of GA + EPK, OM4, spar, & silica, and they were some of the worst results I've had (although all were still 60% 'raw' clay).  Following John B's comments to my previous post, I've adjusted to using 40-45% raw clay, and getting much better results - but haven't tried the GA again.

 

Aside from possibly increasing vitrification, what impact would GA have on plasticity ?  The current blend throws OK for me, but is not as smooth when wedging, etc, as the comercial bodies I've used.  I definitely don't want to make it less plastic.  What about adding bentonite ?  I know it's sometimes added to improve plasticity - would it also affect vitrification ?

 

 

BIG congrats on slugging it out this far!!!!
It looks super good and promising.
Let me know if you need help testing for vitrification/absorption. Which I think should be your next in process.

Welcome to the "I made my own clay" club.

 

Thanks!  I know there are plenty of folks out there scratching their heads, wondering why someone would put the time & effort into making their own clay when "store-bought" clay can be had "dirt cheap".  If I were trying to do this for a living, I would probably agree with them - but as a hobbyist, short of taking advanced college classes, I would never have learned this much about clay if I only used store-bought.  (And, besides, I think it's pretty cool that I'll soon be able to make useable mugs, etc. with the same creek clay I played with as a kid. :) )



#23 Biglou13

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Posted 16 March 2014 - 07:45 AM

GA is a stoneware body it seems to work with what I've thrown at at it. But I've read it's not as plastic as ball clay like om4. And both have lower melt than epk.

Anything you add changes vitrification, but bentonite is usually in very low percentage, usually less than 3%.

While I don't dig my own clay, epk is locally mined close enough to call it local, but not as local as "rockhpper's creek". But my pride level goes up having made it and keeping it somewhat local and indigenous. You'll also be surprised to how much street cred' local self made clay buys!
Caution big brother is watching.
The beige is blinding!!!!!!
The middle of the road is boring

The true sign of intelligence is not knowledge but imagination.
-Albert Einstein




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