[Clayart] fired glaze density differences

Jeff Lawrence jefflawr at gmail.com
Wed Jul 13 11:46:56 EDT 2016

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 LOI
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,
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