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Transparent Clear Glaze


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#1 trina

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Posted 25 September 2012 - 10:39 AM

Hi

Maybe someone could point me in the right direction here. I normally use commerical transparent glaze and fire to 1000C. This glaze works fine and fits my clay. I have the chance to get my hands on about 100kgs of another brand of commerical glaze, (very cheaply hence the question) however this glaze pings and shows very fine cracks on the test pieces, not fitting the clay properly. I have no real experience in glaze mixing, where could I start in adding a flux? What would help?

Thanks Trina

#2 JBaymore

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Posted 25 September 2012 - 11:18 AM

It is difficult to "fix" commercial glazes because you don't have access to the recipe (and hence formula).

You don't need to add a flux. You need to correct the coefficient of (reversible) thermal expansion ... or COE. It neeeds to get reduced (lower COE).

If you knew the formula you could CHANGE one or more of the fluxes used and substitute a flux that has a lower COE. But you don't know what they used, and besides that the stuff is pre-mixed so you can't separate out that raw material anyway.

So what you are really left with is the "standard" trick fopr fixing crazing of adding some small amounts of silica (in a line blend format) using small increments and see if the crazing gets fixed before you start to affect the glossiness of the glass or the transparency objectionably.

If it screws up your work, or takes huge amounts for your (expensive) time to fix,.... it might not actually be a "bargain".

best,

..................john
John Baymore
Immediate Past President; Potters Council
Professor of Ceramics; New Hampshire Insitute of Art

http://www.JohnBaymore.com

#3 trina

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Posted 25 September 2012 - 02:11 PM

It is difficult to "fix" commercial glazes because you don't have access to the recipe (and hence formula).

You don't need to add a flux. You need to correct the coefficient of (reversible) thermal expansion ... or COE. It neeeds to get reduced (lower COE).

If you knew the formula you could CHANGE one or more of the fluxes used and substitute a flux that has a lower COE. But you don't know what they used, and besides that the stuff is pre-mixed so you can't separate out that raw material anyway.

So what you are really left with is the "standard" trick fopr fixing crazing of adding some small amounts of silica (in a line blend format) using small increments and see if the crazing gets fixed before you start to affect the glossiness of the glass or the transparency objectionably.

If it screws up your work, or takes huge amounts for your (expensive) time to fix,.... it might not actually be a "bargain".

best,

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


Thanks John,

I figured that is what you would say. I agree I am happy with the glaze I am using now and it took me quite a while to find it. I buy commercial glazes because I am not the best at mixing and experimenting with glazing. Plus I really hate the thought of losing work to unreliable glazes. Thanks for your input it is greatly appreciated sometimes you just need someone else to see the facts. Trina



#4 trina

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Posted 25 September 2012 - 02:11 PM

It is difficult to "fix" commercial glazes because you don't have access to the recipe (and hence formula).

You don't need to add a flux. You need to correct the coefficient of (reversible) thermal expansion ... or COE. It neeeds to get reduced (lower COE).

If you knew the formula you could CHANGE one or more of the fluxes used and substitute a flux that has a lower COE. But you don't know what they used, and besides that the stuff is pre-mixed so you can't separate out that raw material anyway.

So what you are really left with is the "standard" trick fopr fixing crazing of adding some small amounts of silica (in a line blend format) using small increments and see if the crazing gets fixed before you start to affect the glossiness of the glass or the transparency objectionably.

If it screws up your work, or takes huge amounts for your (expensive) time to fix,.... it might not actually be a "bargain".

best,

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


Thanks John,

I figured that is what you would say. I agree I am happy with the glaze I am using now and it took me quite a while to find it. I buy commercial glazes because I am not the best at mixing and experimenting with glazing. Plus I really hate the thought of losing work to unreliable glazes. Thanks for your input it is greatly appreciated sometimes you just need someone else to see the facts. Trina






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