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How Good Are The Cornish Stone Substitutes?

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I don't have any Cornish Stone or a commercial substitute.


I do use a glaze called  Tenmoku Gold which calls for Cornish Stone - I make my own substitute.


I've got two recipes for that.


Flint/Quartz............. 22

EPK........................ 11

Custer Spar ............67



Custer Spar ...61.3



Whiting....        3.2


I used the second one and also subbed Potash Feldspar for the Custer and China Clay for the EPK. :D


The plate was brushed and the bowl was sprayed (the blobs in the bowl are not Tenmoku gold).




You'll find pics on the net of various items glazed in Tenmoku gold, mine are similar, but by no means identical, but then I'm not Alisa Clausen or anyone else with that amount of experience and skill. -_-






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(Hesitant to say anything about any subs buuuut ...) folks seem to be happy with the H&G sub... worth a try for sure (looks like between $2.70 and 1.50 per pound depending on quantity)

Here's a bit from digital fire Cornwall page:

"It is common to see synthetic substitutes for this material since it is easy to blend other feldspars to approximate the analysis of Cornish stone. These substitutes have the advantage of having no fluorine. Hammill & Gillespie makes one of these, H&G Cornwall Stone. It is described in an article in Ceramics Technical Nov 2011"

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Cornwall is generally not too difficult to replace with other materials in a recipe. It's lower in potassium and sodium than most feldspars, but higher in calcium and silica, which makes it somewhat easy to substitute. There's no direct natural substitute- you can't just use Custer or Neph sye- but you can make your own. Digitalfire uses this:


Dolomite.................... 0.37
Custer Feldspar............. 30.43
Wollastonite................ 3.30
Kaolin...................... 12.85
Silica...................... 29.29
Nepheline Syenite........... 23.75


Personally, I'd just formulate it out. If you don't have glaze formulation software, post the recipe here and we can try it out.

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I'm glad to hear that the decreasing availability of real Cornwall stone will not be an issue. I was thinking about stockpiling a bunch while it is still available, at least from Axner. I do have Insight, so I can mix up some when necessary.

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Cornwall stone is similar to Gerstley Borate in that it is a conglomeration of minerals, and therefore not as consistent in formula as many people would like it to be. It is also more expensive than the ingredients you would use to substitute, since Cornwall has to be shipped over from England. You'll get more consistency and save money if you formulate it out or use a substitute. Even the direct substitutes like Hammill and Gillespie or Laguna's blends are cheaper. Try some reformulations without it, then when you run out you'll know if it's worth buying it again.

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