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, SG5 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, SG5 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 4164392621
Fax 4164387849
 
