Paul Lewing on wed 28 may 03
on 5/28/03 2:51 AM, Dupre Mr Marcy M at dupremm@MSTP.QUANTICO.USMC.MIL
wrote:
> I use Gillespie borate as a 1:1 substitute for Gerstley borate. Do any of
> you know if there is a limit to the amount of borate that should be put in a
> glaze to minimize this bubbling, spitting activity?
Tig, I'm not that familiar with Gillespie Borate, in fact, I've never tried
it. But I've used a lot of Gerstley and done some testing with Laguna
Borate and Boraq and some of the other GB substitutes.
If Gillespie is anything like Gerstley in physical properties, it takes a
long time to dry. And I think this is your problem. I'd bet you put those
pieces into the kiln before they were really dry. I don't think the stuff
is bubbling and spitting as it melts, I think it's popping off as it's
drying.
As far as how much of one of these borate materials you can put into a
glaze, one of the most popular cone 6 glazes around is 50% Gerstley, and the
rest kaolin and silica. So you can have lots of this stuff in a successful
glaze.
Paul Lewing, Seattle
Dupre Mr Marcy M on wed 28 may 03
Dear All,
I recently unloaded a kiln and found a lot of splatters on the shelves
around where I had pots with glazes containing Gillespie borate in the
recipe. The patterns looked like there was a lot of boiling activity,
popping and exploding off the pot. I know that the borate family has a
tendency to do this, but I didn't realize it was so heavy.
I use Gillespie borate as a 1:1 substitute for Gerstley borate. Do any of
you know if there is a limit to the amount of borate that should be put in a
glaze to minimize this bubbling, spitting activity?
Thanks in advance,
Tig
in soggy Springfield, VA
John Britt on wed 28 may 03
Tig,
If you fire too fast from between 600 F -1200 F when the borate is letting
go of its chemical water it causes that "spitting" or "butterfly rolls" in
the glaze.
Try slowing it down a bit,
John Britt
Penland Clay
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