Dave Finkelnburg on sun 21 nov 99
------------------
Glaze gurus,
As some of you recall, I have been struggling with blistering on a glaze=
I
found in Chappell. after numerous tests I've concluded my basic fault has =
been
simply overfiring the glaze. I understand some of the idea of glaze =
calculation
and limit formulas, such as the differences in alumina, silica between cone =
5
and cone 10 glazes. However, I am really not sure how to calculate a range =
for
testing to adjust this glaze to fire up only one or at most two cones. Can
someone please explain to me how to predict the change I need to make, or =
where
to find that information please? Thanks=21
The base glaze I am using, SG-5 in Chappell, is:
Gerstley Borate 51
Silica 31
Kaolin 16 (I use EPK)
Custer Feldspar 3
Bentonite 1
At cone 4 this fires quite smooth, at cone 5 I get a few small blisters =
with
copper oxide addition, at cone 6 the blisters become noticeable, at cone 7 =
they
go wild=21 :-(
I assume the fundamental problem here is oversupply of the flux Gerstley
Borate. Is that the case?
What information have I left out? Thanks in advance for any help=21
Dave Finkelnburg
dfinkeln=40cyberhighway.net
Ron Roy on tue 23 nov 99
I'm getting tired of dealing with this glaze - I don't like it - I think
it's dumb and I wish it would go away.
Hi Dave - this is not aimed at you - just some frustratation coming out.
This following recipe is a more balanced glaze - make up 500 grams of it
and 500 of the original and do a 5 part line blend and tell me what happens
- please.
Sieve 2 times through 80m.
After dipping in # 1(your original) and #5 (my revision) take equal amount
of #1 and #5 to make #3 (you will need twice as much of #3 cause you will
need to mix it with #1 to get #2 and again with #5 to get #4 - equal parts.
When you have dipped into #2 and #4 mix it all together to get #3. Fire to
cone 6 (use a large cone beside the tests)
My revision.
Gers Borate - 32.0
Custer - 28.0
Wolastonite - 5.0
Strontium Carb - 3.0
EPK - 11.0
Silica - 21.0
Bentonite - 1.0
Total - 101.0
There that feels better.
It would be even better if you would let me do this with some frit 3134 -
then it would be much better.
RR
>----------------------------Original message----------------------------
>Glaze gurus,
> As some of you recall, I have been struggling with blistering on a glaze I
>found in Chappell. after numerous tests I've concluded my basic fault has been
>simply overfiring the glaze. I understand some of the idea of glaze
>calculation
>and limit formulas, such as the differences in alumina, silica between cone 5
>and cone 10 glazes. However, I am really not sure how to calculate a range for
>testing to adjust this glaze to fire up only one or at most two cones. Can
>someone please explain to me how to predict the change I need to make, or where
>to find that information please? Thanks!
> The base glaze I am using, SG-5 in Chappell, is:
> Gerstley Borate 51
> Silica 31
> Kaolin 16 (I use EPK)
> Custer Feldspar 3
> Bentonite 1
>
> At cone 4 this fires quite smooth, at cone 5 I get a few small
>blisters with
>copper oxide addition, at cone 6 the blisters become noticeable, at cone 7 they
>go wild! :-(
> I assume the fundamental problem here is oversupply of the flux Gerstley
>Borate. Is that the case?
> What information have I left out? Thanks in advance for any help!
> Dave Finkelnburg
> dfinkeln@cyberhighway.net
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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