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Humboldt Potter

Clear Glaze Is Crazing On Cone 10 Babu Porcelain.

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Hi all, I have been throwing with Babu porcelain, glazing with Reeve's Clear glaze. I fire to cone 10, in a light reduction, gas kiln. I notice that the Reeve's clear seems to craze more than I want in a food vessel, even when thinly applied. It seems to fit stoneware better than porcelain, with much less crazing. I know Babu shrinks more than stoneware, so it's clearly a glaze fit issue.

Has anyone found a better clear glaze that doesn't craze, for use on cone 10 porcelain? Do you have any suggestions as to how I might get a better glaze fit on Babu? I use Babu because of its clear, white color. I'm willing to use a different porcelain if I can get better results and keep the white color. Any ideas? It's very frustrating. I want to use this clear base and add colorants, such as Mason stains to get translucent, "celadon-like" colors. Thanks for any help.

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Mark C.    1,806

I have good clear formula I will PM you-looks like you live close by-same county at least.

The only way is to test various clears on Babu (shrinks15%)- I have has no issues with Daves porcelain (shrinks13%) 

most stonewares are in that 12% range

Check your PM box

Mark

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JBaymore    1,432

The overall firing shrinkage (like 12% , 15% etc.) has nothing to do with crazing.  Crazing and shivering are based on the COE (Coefficient of Thermal Expansion) of the body relative to the COE of the FUSED glaze.  COE and total firing shrinkage are not necessarily related.

 

To fix crazing, try adding a little silica as mentioned above.  Use line blend procedures for the tests.  If that does not work use glaze calc software to substitute the higher COE fluxes with lower COE fluxes.

 

Modifyinjg the body is another option... but if you are usingt commercial formulations... likely not easily possible.

 

best,

 

.............john

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neilestrick    1,381

Just using a different glaze won't necessarily help. You could try 20 clear glazes and they could all craze. Most glazes need to be modified for the clay body you are using. As stated above, try adding silica in 2-3% increments, or equal parts silica and EPK to better maintain the Si:Al ratio. Babu is awesome stuff!

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