[Clayart] tony's metaphor tangent - cornwall stone vs custer mega-pinholes

ronroy at ca.inter.net ronroy at ca.inter.net
Sun Mar 9 17:08:08 EDT 2014

Hi Jeff,

The answer to the difference in the recalculated glazes may lie in the  
differences in the analysis of cornwall stone. There are 4 listed in  
Mimi Obstler's "Out of the Earth into the Fire" - page 20.

ISBN 1-57498-001-7 hard cover
ISBN 1-57498-008-4 soft cover

Who knows which version was being used at Alfred U.

2 versions have some P2O5 and 3 versions have Fluorine. 3 versions  
have under Under 8% alkalis equally divided between Sodium and  
potassium and one version has less than 6% and mostly K2O.

I would say that having the right analysis for the materials in the  
original glaze would help a lot.

I do agree that getting the same result without a material like  
Cornwall Stone is going to take some special skill -  but - it is a  
magical material in some ways.


Quoting Jeff Lawrence <jefflawr at gmail.com>:

> A real-life vignette:
> Kathleen: What do you suppose is happening with this glaze? It behaved
> perfectly but now it's  pinholed on one side.
> <Val Cushing's Blue Green
> 1380 Cornwall Stone
> 1020 Whiting
> 600 EPK
> 120 tin oxide
> 120 copper carbonate
> Jeff <channeling Tony>: No idea, but it's a long swim for all that Cornwall
> Stone. Let's make it with somethign  more local.
> < Two spot-on oxide matches ensue from Glazemaster, one with G-200 and one
> with custer - here's one:
> VC2
> 298.3 custer feldspar
> 1053.9 whiting
> 772.3 epk
> 421.3 neph sy
> 454.2 silica
> 120 tin oxide
> 120 copper carbonate
> <upon opening after the 10R firing  this morning >
> Whoa! Both those tests are gaudy (and runny) turquoise lava glazes on flat
> pieces and run off a test cup (Original was a mat turquoise).  Wuzzup with
> that?
> ...
> <vignette mode off>
> This shows why normal people like stuff that works no matter how long the
> haul to get it, but me, I get sidetracked - why the frozen froth in the
> tests when the oxide balance was so close? What's bubbling? I thought
> whiting lost its CO3 well below  cone 10.
> Theories, please!
> Thanks,
> tangentially yours,
> Jeff
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Ron Roy
ronroy at ca.inter.net

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