David Hendley on fri 22 oct 99
Glass cullet fills the bill as a low (almost no) alumina
alternative to feldspar.
Sodium is the main flux in cullet, and the silica content
is lower than that in feldspar or nepheline syenite.
It does seem to be ever-so-slightly soluble, like
The price is sure right - free, and it's a very efficient way
to recycle, since the material never has to leave your place.
Years ago I started using cullet in slip glazes, to end up
a glossy glaze, but with very high clay content so the
glaze could be painted on wet pots.
I think the Cranberry glaze could certainly benefit from
cullet, so some clay could be added to the slop without
raising the alumina content.
I don't agree with John B. that a very high alkaline
content is required for a good copper red glaze.
It's possible to formulate a copper red that fits
within the limit formulas, doesn't craze, doesn't
run, and exhibits good color.
----- Original Message -----
From: Craig Martell
Sent: Thursday, October 21, 1999 9:50 AM
Subject: Re: Pete's Cramberry stuff
| ----------------------------Original message----------------------------
| Hello John:
| Thanks for the post about the cramberry glaze.
| Your point about the alumina content of spars is, or course, right on
| target. When I was working on some shino sets with Jim Robinson, we took
| the same stance with kaolin as the added alumina source since it also
| contributes silica. We used alumina oxide and the results were much more
| dramatic and accurate.
| Since we are in such a pinch for sources of insoluble potash and soda, I
| looked at some frit analyses and I think that a combo of f-4 soda spar and
| frit 3269 would yield a "c" corner glaze with much less alumina than just
| custer spar or a sub of g-200 or kingman. Buckingham spar offers less
| alumina too but isn't available any more. The awful truth is that we
| can't totally eliminate alumina from the flux corner glaze in a Currie set
| of copper reds. I think his whole approach is to work with what's
| available and make mental notes of variations and nuances. It is
| true that "you can't get there from here", so we do the best we can with
| what's available.
| Thanks again for a well thought out post. Craig Martell in Oregon