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#21 oldlady

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Posted 17 November 2012 - 12:59 AM

john,

thank you for the clear explanation of the problems in the glaze recipe. i read it all and it makes sense. i am not a chemist and really cannot manage to think of one more complicated thing such as how to fix the recipe. i fire only 8-10 times a year so i do not have a way to "play" with the ingredients. (i would rather have a root canal)

if you have any suggestions i would welcome them. i know i have used copper carb at least once when i mixed this glaze since i had no copper oxide. and i have only had cobalt carb so no cobalt oxide it that batch, either. i recently got both oxides just so i could mix this glaze since i am down to what is left in the sprayer bottle and none in the bucket. wont be mixing it now.

have you any thoughts on the red glaze? it really is a pretty color and i would love to be able to use it....SAFELY!!
"putting you down does not raise me up."

#22 pricklypotter

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Posted 26 November 2012 - 11:47 AM

john,

thank you for the clear explanation of the problems in the glaze recipe. i read it all and it makes sense. i am not a chemist and really cannot manage to think of one more complicated thing such as how to fix the recipe. i fire only 8-10 times a year so i do not have a way to "play" with the ingredients. (i would rather have a root canal)

if you have any suggestions i would welcome them. i know i have used copper carb at least once when i mixed this glaze since i had no copper oxide. and i have only had cobalt carb so no cobalt oxide it that batch, either. i recently got both oxides just so i could mix this glaze since i am down to what is left in the sprayer bottle and none in the bucket. wont be mixing it now.

have you any thoughts on the red glaze? it really is a pretty color and i would love to be able to use it....SAFELY!!


The green/blue glaze: using copper carb lowers the effective amount of copper in your glaze. if you use copper carb and want to keep the same 'recipe', you should use more since copper carb "=" copper ox + CO2 that burns off in the kiln (LOI).

i would go two ways:

1 does the glaze REALLY need so much copper and cobalt? the fact that you once used carb instead of ox and got the same colour response suggests that it doesn't. I would go in the direction of lowering the oxides and seeing if i still get the same colour response. cobalt too is a powerful colorant, 2.5% is a lot and you can probably do with less

after lowering the amount of oxides, try to make the glaze base itself more durable:

2 also, add clay (= alumina) and silica to see if i still get the same surface and colour response

each of those steps should ideally be done on a grid of 25-35 paper cup test batches, all test tiles fired in the same firing. in the end you will be able to choose a glaze that has the more or less same colour and surface but is safer to use and more durable too.

no advice about the red. :( there is a certain kind of red that i wouldn't use no matter how many times they put 'non toxic' on the label.




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