Karl P. Platt on fri 11 jul 97
> I have never before encountered such
> a phenomina. Does anyone have some theories? The formula
> is as follows:
>
> Silica 27.7
> EPK 18.18
> NephSy 18.18
> Dolomite 9.09
> Gerstly Borate 9.09
> Talc 9.09
> Bone Ash 9.09
> Iron 9.0
This is a textbook example as to why Ghastly Borate is a pariah
--
Heisenberg may have been here.......
Craig Martell on sat 12 jul 97
At 01:47 PM 7/11/97 EDT, Karl Platt wrote:
>This is a textbook example as to why Ghastly Borate is a pariah<
If you think Gerstley Borate is bad try using Colemanite sometime!
Remember folks the correct name for the material is "Gerstley:, not
"Ghastley". A while back, someone actually submitted a glaze receipe with
"Ghastley Borate" listed as an ingredient. This poor soul was an obvious
victim of your anti-Gerstley Borate campaign. It's wearing a bit thin!
I use Gersley Borate in two copper red formulas with similar oxide contents
to the Berry Rust glaze, and in larger percentages that 9.0, and have not
had the grit problem. A person who uses Gerstley Borate in glazes needs to
make some small adjustments in the application of the glaze and there is an
"orientation time" spent in getting used to the material. In general, it
works well and is a good source of Boron in glazes. Sure, frits work
better, but they are more expensive and sometimes hard to come by. If I can
use a natural, unfritted material, I'll go for that, before I use frits.
My apologies for not addressing the actual problem of grit in the Berry Rust
glaze, but I really don't have any ideas. I don't think it's the GB though.
If you do Karl, why don't you offer an explanation as to what's happening
and why the GB is causing the grit problem? I would honestly be interested
in knowing the mechanics of the problem.
Regards, Craig Martell-Oregon
June Perry on sun 13 jul 97
The grit may be from the bone ash.
Regards,
June
Ron Roy on mon 14 jul 97
Karl wrote:
>This is a textbook example as to why Ghastly Borate is a pariah
Notice what was left out in his reply:
"I have used this same batch (Gerstley Borate) in other glazes and not had this
problem."
I can only guess why Karl has such an intense dislike of such a useful
material for those working below cone 10. I can only assume GB is a
nightmare for anyone trying to make glass.
I have used this material for over 35 years and have never had a problem
with it. There where times when my suppliers sent improperly ground GB -
some of which would sit on an 80m sieve but that is a different subject.
I would suggest the materials which are much more problematic are the Neph
Sy and the Iron.
I am having a problem with "clumping" (my word) - hard lumps of glaze
forming in my tenmoku glazes (7.5% Iron - no GB) These lumps are forming
about half way down in the bucket (after the glaze has been sitting around
for a while) in a hard layer with soft glaze under. My frind Bob Bozak is
also having the same problem with a glaze with Iron and BoneAsh. Both
glazes are thickening as well - anyone have any ideas about what is going
on?
Gerstley Borate has a great advantage over frits. It is half the price of
frit, it helps suspend glazes and addes to the toughness of the raw glaze
on the pot. It also provides many trace amounts of oxides not found in
frits - the net result being better melting at the lower temperatures.
I do think you can have too much in a glaze but it is a rather simple
matter to replace some of it with an appropriate frit.
Neph Sy is, in my opinion, a problematic material at cone 6. Sodium is
released into the glaze slop and, in some cases deflocculates the batch. On
top of that it supplies more alumina than all the other spars. This allows
for less clay in the batch adding to the susension problem caused by the
sodium.
I would like to know exactly why anyone thinks Gerstley Borate is a problem
- what is leaching out? What are the effects of that leaching and what
would be the counter measures?
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/ronroy.htm
June Perry on tue 15 jul 97
Dear Ron:
I think the big problem with Ghastly Borate and Colemanite is that fact that
the glaze fattens up because of gases released when the glaze sits for a long
time. The only way to counter-act that, I understand, is to let the glaze dry
out totally and then re-add water and mix. The release of the gases makes the
glaze fatten up and seem too thick. So the unknowing potter, adds more water
to thin the glaze and winds up with a pot with a thin, dry coating of glaze.
But I know that you already know this so maybe your asking another
question??????
Warm regards,
June
Sandra Dwiggins on wed 16 jul 97
June---
I didn't know that thoroughly drying out the glaze and remixing would
solve the thickness problem. Do the gases form again when you remix
the glaze after drying, and does the glaze thicken up again? Can the
remixing be done endlessly?
Sandy
June Perry on wed 16 jul 97
Dear Sandy:
It is the released gases that are expanding the glaze, making it appear too
thick. Supposedly the drying out gets rids of it. It will probably re gas it
is sits for a long while. I don't see any reason why you couldn't redry
repeatedly. Maybe others who have done tried it can jump in here.
Regards,
June
| |
|
