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Converting the firing range of a glaze?

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So to convert a glaze from high fire (cone 9) to a mid range do you increase the flux? What would you replace it with? Or ?? I’m trying to wrap my head around the chemistry of converting. I’m currently in love with a recipe from Tom Tuner but it’s cone 9. Thank you! 

Edited by Rebekah Krieger
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oh dear! Now I feel silly.  I have all of those. I apologize for the confusion. I’m fairly new to glaze mixing. I have altered a few recipes but now I am in the process of learning how to construct my own. Thank you 


 So what do you substitute 5%  of the silica with that? 

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Maybe some simplicity actually. Most things are cone 10 ish because of the geology of the earth and that is where things melt. Several ways to get low: less silica and alumina; however you are constrained by your feldspars and clays. More flux including high levels of lithium or a Bristol glaze using the appropriate portions of zinc in a 0.7 Ro base, and finally, Boron! So it turns out approximately 0.15 Boron (+/- 10%]  (UMF) is ideal for cone six.

Boron can be obtained from Gerstley, Gillespie, and Frits to name a few. The easy way is to find a suitable Boron source that can be added to your recipe while adjusting the flux and surface texture to match the original. It’s actually much easier than it sounds but as in all things likely progressively fired to obtain a texture and color match as close as practical to the original.

that would be the hard part.

Edited by Bill Kielb
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