Lili Krakowski on thu 11 jan 07
Via Mel, Diane posted a glaze called Buttermilk. This glaze supposed to be
a c.9-10 has big blisters on it at that temp, but
improves at c.11.
The given recipe is
GerstleyBorate 10.5
Dolomite 6.8
Whiting 9
Custer Spar 29.3
EPKaokin 6.8
Talc 13.5
Flint 24.1`
Zirconium 8
Now my suspicions were aroused when this did not add up to 100. I said to
myself said I: "Somebody putschkied with this glaze and got it out of
kilter." Which really did not help.
I then fed it into GlazeMaster(TM) and learned this:
Na2O .047
K2O .07O
MgO .361
CaO .522
Al2O3 .196
B2O3 .103
SiO2 2.432
Which yields a COE of 60.71
The Zirconium is not in the program so I do not know how it affects the COE,
but my guess is not much, and not for the better.
Ok. Now I know that the alumina and the silica in this glaze is ok for a
c.6 glaze but well below the limits for c.10.
I consulted Fraser"s "CERAMIC FAULTS and their remedies" which confirmed my
notion that the glaze was overtired and just plain boiled. He also says that
zirconium glazes are notorious for causing blisters, but I do not know as I
do not use Zinc. in glazes.
Then just to step back a bit, I looked up Alisa's Dolomite glaze which is
c.6 and very very nice.
Formula:
Na2O .103
K2O .033
MgO .493
CaO .371
Al2O3 .218
SiO2 1.979
NB that Clausen does not have any B2O3, has MORE Alumina (the most
refractory component, if Zirc is left out).
So. In my opinion you have there a c.6 glaze that for some reason is listed
as c.9 or 10. My guess is that it WAS a c.9 or 10 and then in the great To
Six Rush of a few years ago someone modified it, and forgot to change the
cone number in the listing.
I therefore also think that when you originally used this glaze it WAS a
c.10 and so it worked for you. When you looked it up it had been changed.
As to why it heals over at 11-- my guess-and it is just that--is that at 11
the poor thing is SO melted it has been absorbed into the body, and very
little is actually left on the surface.
My cure would be to up the clay in 5% increments.
Now. Kathryn. THIS is why whether with pencil on the back of old envelopes,
with a calculator, or with a glaze program it is good to figure out
formulas. It just makes life easier, and leads one far more quickly to
possible solutions of problems.
Lili Krakowski
Be of good courage
sacredclay on fri 12 jan 07
-My dear Lil, I am so fired up to go get this Glazemaster!I know my
boss just got one, so I am going to tap on his shoulder, point to the
far corner to distract him and say "Look over there!" and grab the
thing and run! Or I could ask him nicely to share, but that takes the
excitement out of my life. Thanks so much for really clearing this
thing up. The fog has finally lifted. Much love to you and all,
kathryn in > Now. Kathryn. THIS is why whether with pencil on the
back of old envelopes,
> with a calculator, or with a glaze program it is good to figure out
> formulas. It just makes life easier, and leads one far more
quickly to
> possible solutions of problems.
>
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> Lili Krakowski
> Be of good courage
>
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