[Clayart] zinc oxide in reduction

Vince Pitelka via Clayart clayart at lists.clayartworld.com
Sun Aug 24 09:27:29 EDT 2014

David Hendley wrote:
"I did some research on this 15 years ago. Not definitive, but worth noting.
I went through all my many glaze recipes collected through the years and selected 8 or 10 with high percentages of zinc oxide. I mixed up test batches. Then I mixed variations, first  with the zinc oxide removed, and then with the zinc oxide replaced with more of the other fluxes in the glaze.
The results were that for about half the glazes the zinc oxide seemed to make no difference - all the variations looked the same. But, for the other half of the glazes, they looked substantially different when the zinc was removed. Of course this doesn't offer any insight as to what is happening, but it does prove that zinc oxide can have a noticeable effect in a glaze fired to cone 10 in reduction."

Hi David - 
Thanks for posting this. Yes, it's not definitive, but it certainly does help. Maybe at some point I can do some serious research into this.  It's so easy to assume that all the zinc volatilizes and escapes and thus is irrelevant, and yet as you point out, the zinc does seem affect the appearance of the some cone-10 reduction glazes.  I suppose at least part of the question here is the degree to which reduction affects materials deep within the molten glass.  If some of the zinc remains within the glaze as highly refractory ZnO, then it is logical to assume that it will affect appearance.
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka at dtccom.net   

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