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Glaze from clay body?

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Hey all

Being rather new to glaze formulations, I want to experiment with using a fluxed clay body (extra black stoneware max. 1200degC) as a glaze for single fire/raw glazing of japanese-inspired yunomis/tea bowls made from the same clay. The clay has such an amazing black bordering metallic color when fired to maturity, whose character I would love to retain partially in a glaze to line the inside of the bowls.

I have some twice-sieved hardwood ash that I want to add as a flux (for cone 5/1200C oxidation) and probably will require an additional flux (GB maybe). I understand this will require experimentation which I am now planning, but before I do I am curious if anyone has any tips/advice on doing this, perhaps some rough ratios as a starting point. Hoping to create a not too glossy /satin glaze (or perhaps more appropriately said a well-fused slip-based engobe) with minimal ingredients (clay body, wood ash, perhaps secondary flux and/or feldspar). 

Any pointers/advice would be greatly appreciated.


Joris (the Netherlands)




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You could treat as a glaze component but you will need the chemistry. From there pop it into a glaze calculator, set your fluxes in the range of 0.3-0.7 and add about 0.15 boron under UMF. At this point you would simply be making a glaze with it though, albeit potentially a durable liner glaze. That could give you a quick idea on the direction to go.

Edited by Bill Kielb
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 Try a triaxial with a 50:50 mix of boron frit (or gerstley borate) and nepheline syenite as one point, your clay as second point and ash as the third point. If you haven't done a triaxial before chart below shows how to blend. Basically you will be having 3 ingredients which will be blended together in different ratios. Might take  few triaxials to get it nailed down but definitely should be doable. If it's too fluid then decrease the flux in a line blend. Fire your tests on waster pieces of clay and/or use little bowl shaped test pieces and just glaze the insides.


Edited by Min
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glazy has a lot of good info on blend testing:



i've been doing some ian currie style volumetric blends of a glaze recipes

details for that method:

pretty good video explaining it:

one of my tests:



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