Jan Lipuma on thu 23 apr 98
Dear kind glaze gurus,
For over 10 years I have used the following ^6 glaze called Counts
Colemanite. Two dips/pours over a black waxy yields a dark midnight blue
with a lot of depth (and a lot of customer appeal). It has always been a
difficult glaze to handle because it settles quickly, dries very powdery,
and runs badly if too thick.
This year it has begun behaving irratically. Now it runs like a *#!!@###,
and crawls in spots. For some reason I don't understand, whenever I add
2% bentonite to help keep it in suspension, it is much more likely to
crawl. What is going on with this? 2/3 of the last kiln load were
sacraficed to the hammer, the other third were ok. Talk about intermittent
reinforcement!
During the gastly borate thread, I thought that was the problem, then
during the whiting thread I changed from my new supply of whiting from New
York to some from Tennessee (where my earlier supplies came from and was a
different color), and began thinning it to no more than 1.13 SP.
Colemanite Glaze ^6 from Charles Counts:
Frit 3134 25.23
Neph Sny 34.93
Whiting 5.64
Colemanite (I use GB) 5.07
Ball Clay 3.66
Silica 25.35
--------
100.
Copper Carb 5.
The orders are backing up and I can't seem to solve this . Some firings
are ok then whammy!
Any help from someone with glaze calc would be appreciated.
Thanks,
Jan Lipuma
Lexington KY
Craig Martell on sat 25 apr 98
At 07:35 AM 4/23/98 EDT, Jan wrote:
>----------------------------Original message----------------------------
Hi Jan:
Here's the calculated glaze.
Untitled Recipe 1
FERRO FRIT 3134 25.23 CaO 0.57*
NEPHELINE SYENITE 34.93 MgO 0.00*
WHITING 5.64 K2O 0.06*
GERSTLEY BORATE 5.07 Na2O 0.36*
OM#4 BALL CLAY 3.66 Fe2O3 0.00
SILICA 25.35 TiO2 0.00
======== B2O3 0.42
99.88 Al2O3 0.32
SiO2 3.46
Cost/kg 0.97
Si:Al 10.99
SiB:Al 12.31
Expan 7.76
This is a well balanced cone 6 glaze according to the limit formula stuff in
Insight. All of the fluxes are near their upper limit though and that may
be part of the problem. The glaze may have a very tight maturation or
firing range and if you get it a bit too hot it runs. You might try some
tests with kaolin instead of ball clay, and you might raise the kaolin in 5%
increments, maybe up to 15% and see if this gives you a better firing range
without disturbing the aesthetics of the glaze. Raising the clay and
changing to kaolin may help with the powdery surface thing and the crawling
too. Is it crawling where applied over the black glaze, or just where this
glaze is applied solo, or all of the above??
Hope this is of some help until a REAL guru replies. Craig Martell-Oregon
Craig Martell on mon 27 apr 98
>>----------------------------Original message----------------------------
>
>Hi Jan:
>
>Here's the calculated glaze.
>
>Untitled Recipe 1
> FERRO FRIT 3134 25.23 CaO 0.57*
> NEPHELINE SYENITE 34.93 MgO 0.00*
> WHITING 5.64 K2O 0.06*
> GERSTLEY BORATE 5.07 Na2O 0.36*
> OM#4 BALL CLAY 3.66 Fe2O3 0.00
> SILICA 25.35 TiO2 0.00
> ======== B2O3 0.42
> 99.88 Al2O3 0.32
> SiO2 3.46
Hi:
I'm replying to my own message, which is above. I suggested that Jan raise
the clay and possibly change it to kaolin to give this glaze a wider firing
range. I missed an important point that was brought to my attention by Tom
Buck. This is a copper blue glaze that relies on a certain ph to be
alkaline enough to produce the copper blue. When you up the clay and, or,
change to kaolin you are making the glaze more acidic and may change the ph
enough to make it a green glaze instead of a copper blue. One would have to
do some testing to see what's tolerable and possible.
regards, Craig Martell-Oregon
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