Earl Brunner on thu 3 sep 98
I teach beginning and intermediate wheel throwing at our local community art
center. We fire to cone 5-6. Many of the beginners get their first glaze
satisfaction from the interesting affects that they can get from overlapping
different glazes (we won't go into what that does for my kiln shelves).
Recently I have noticed that a number of the overlap combinations will not
adhere to each other. This is a new phenomenon. The applications are not
overly thick, and yet if they are overlapped they either fall off the pots
before firing or if I didn't catch them, during the firing. Being a male,
(and I think this is in the realm of asking for directions while driving in
unfamiliar territory) I have never used "sissy" additives in my glazes. This
is sort of new territory for me, I've had little or no experience in this
area. What can/does one add to wet glaze to give it unfired strength and help
it adhere better?
Earl Brunner
phyllis michele greenhouse on fri 4 sep 98
> I have never used "sissy" additives in my glazes. <<
dear macho man potter (ahem) earl :)
sorry to hear that you consider a great glaze additive to be of the
"sissy" ilk, but all i gotta say is, IF IT WORKS, DON'T QUESTION IT" ....
what i have found to be a reliable source in my functional glazes, (where
i overlap 4 glazes, same base, different colors) over a base coat of a
heavy iron bearing glaze, is the readily available additive "CMC" ...
this suspending agent is very useful in glazes as a binder and also aids
in surfaces that might be powdery or flake off during drying or
firing.....the true name for this chemical is CARBOXYMETHYLCELLULOSE, if
you cannot find it as "CMC", however, most ceramic suppliers carry this
invaluable product...additionally, bentonite, which doubles as a
suspending agent, and also a binder...(not more than 2% per batch) can
also be used...
please let us know if this helps...
phyllis michele greenhouse
earthspinner
rapture@accesspro.net
http://www.accesspro.net/rapture
Linda Blossom on fri 4 sep 98
Earl said: =22I have never used =22sissy=22 additives in my glazes.=22 Are =
you
referring to the additives (gum and synthetic gums) as =22sissy=22 because =
they look
like gelatin that is found in jello and is used by some, usually females, =
to
make their fingernails harder? Glad I don't suffer that particular bias - =
using
additives seems a good practice to me. However, I doubt that they will make =
two
glazes compatible that aren't. I will admit to thinking that automatic
transmissions are =22sissy=22. However, that is only my opinion. I would =
never say
that everyone should drive standard shift.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
6075397912
www.artscape.com
blossom=40lightlink.com
Paul Lewing on fri 4 sep 98
Earl,
Why this should work, I have no idea (maybe some less
chemistry-challenged people out there can explain) but you might try
mixing your glazes up with lots of water, and siphoning it off. Add
new water and do it again. This has dramatically reduced crawling for
me, especially when I overlap different glazes. It has made the
biggest difference in scrap glazes and, oddly, a commercially made-up
fritted glaze that I buy dry. I should also credit this trick to
Louis Katz, who mentioned it in a discussion of dealing with scrap
glaze here a year or so ago. Now I do it to all my glazes.
Paul Lewing, Seattle
Earl Brunner on sat 5 sep 98
thanks, many of the glazes do have bentonite in them already, looks like I'm
in the market for some cmc. Seems to be the concensus.
Earl Brunner on sat 5 sep 98
In a message dated 9/4/98 5:41:27 AM Pacific Daylight Time,
blossom@lightlink.com writes:
<< Are you
referring to the additives (gum and synthetic gums) as "sissy" because they
look
like gelatin that is found in jello and is used by some, usually females, to
make their fingernails harder? >>
SORRY, I hit a nerve with that one didn't I? I dont' know WHAT you are
talking about. Fingernails? I chew mine. Regularly.
Ron Roy on sat 5 sep 98
Hi Earl,
This usually has to do with the unfired strength of the clay in the glaze -
kaolins usually are not strong. Ball clays are stronger generally and
bentonite can do the job as well.
My usual approach is to replace some or all of the kaolin with a ball clay
- on a molecular level. This means you can get more clay in the glaze
simply because you need more ball clay to get the same amount of alumina
the glaze calls for. A simple addition of 1 or 2 % bentonite will probably
work to toughen the raw glaze - thats the quick answer.
There are times when raw glazes crack when they have too much clay -
finding a clay with higher green strength (MOR) might be called for but I
would also try the same technique as above - replace some of the current
clay with ball clay and/or add a small amount of bentonite.
If you need help reformulating just send me some recipes to work on.
>----------------------------Original message----------------------------
>What can/does one add to wet glaze to give it unfired strength and help
>it adhere better?
>Earl Brunner
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Earl Brunner on sun 6 sep 98
In a message dated 9/5/98 9:36:48 AM Pacific Daylight Time, ronroy@total.net
writes:
<<
My usual approach is to replace some or all of the kaolin with a ball clay
- on a molecular level. >>
yeah, I'm really having to re-evaluate the glazes in the studio anyway. There
are some that make me shudder, given the novice nature of the students using
the studio. Potassium dichromate glaze labeled "do not use on food dishes",
nothing about dangers of handling in the green state (I reformulated it to
remove the potasium dichromate) and changed the label. Lots of barium in lots
of the glazes, I think I can cut back. Lots of Gerstley Borate with its
soluability. Will look at the clay content as I do so, andprobably add a
little gum.
Thanks everyone who has replied.
Earl Brunner
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