[Clayart] fired glaze density differences

David Hendley david at farmpots.com
Wed Jul 13 14:00:27 EDT 2016

I have used the this rutile/iron overglaze for many decades.
I love the color as well as the crystallization, and I know what
you are referring to.
I have always assumed that the overglaze is much more
fluxed than the glaze, which allows everything to melt more
and thus the glaze melts more and runs, causing an extra
thick glaze to thin and spread out.
Who knows, just my guess.
David Hendley
david at farmpots.com

----- Original Message ----- 
> I tried out a gerstley-iron-rutile (1:1:1) mix that a number of 
> clayartisti
> mentioned in the past and quite like the goldish color that results. 
> Thanks!
> When I blob it onto a glossy celadon that likes to be thick, the fired
> result is a distinct indentation in the overall glaze coating where the
> blob was. My first thought was this was just mass loss from firing
> (gerstley borate has LOI of 25% or so)  but then I realized the overlay 
> should really only explain blob shrinkage, not the additional thinning of
> the underlying glaze.
> My current hypothesis is that the constituent mix forms a glass that is
> denser, and therefore thinner, than the celadon by itself. However, since
> the blob-celadon mixture layers are about half the thickness of the 
> celadon
> layer, I can't even persuade myself with this account.
> Anybody got a better explanation?
> Thanks in advance,
> Jeff
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