B A HARPER on sun 8 feb 98
Hi everyone -
I have a nasty bloating problem with this clay body :
Lincoln Fireclay 100
Cedar Heights Goldart 100
OM #4 Ball clay 50
Soda Feldspar 25
Silica sand 5
Yellow Ochre 2
Does anyone know why this clay is bloating ?
I've fired some green and some bisqued pieces, all to cone 10 and
they all bloated. I fired pretty slow up to and through quartz
inversion, then fairly fast until the end. I did a strong 25 min.
body reduction around 06, then a light/moderate reduction until the
end, with a 30 min. soak in light reduction as cone 10 was at about
10 o'clock. The kiln is a natural gas, updraft West Coast kiln and
the bloated pots where almost right in the center of the kiln.
Thanks in advance for any help -
Brian Harper
Duane Littell on mon 9 feb 98
-------------------
Brian,
Goldart is high in sulphur. OM 4 is high in carbonaceous material. Bisque =
to
cone 04, oxidation, your concern should be with the Meta Kaolin phase and =
not
quartz inversion in reference to bloating. Body reduction at cone 06. =
Remember
smoke doesn't equal reduction=21
Dr. Biz
Tony Hansen on tue 10 feb 98
Is your clay bloating because it is too vitreous.
Most clays containing fireclays cannot be fired to zero porosity, and
at some point above that they reach maximum strength. A buff stoneware
I use is optimal at 1.5% porosity. If I fire it higher to 1% porosity
it will bloat some of the time. If I fire it to .75% porosity it will
bloat all the time.
--
-------
T o n y H a n s e n thansen@digitalfire.com
Get INSIGHT, Magic of Fire at http://digitalfire.com
Louis Katz on tue 10 feb 98
I would suspect that the Goldart that you have has too much sulfur in
it. If your bloats are not darker than the rest of your clay when broken
open then that clinches it.
More oxidation will not help if this is the case. Reducing for a little
while at cone 08 or so might help. This reduceds the sulfur compounds
and allows them to evaporate easier at a lower temperature. The best
solution is to exchange something with the Goldart like Roseville or
some similar clay.
If the bloats are dark then I would suspect the Lincoln or unmixed
yellow ochre. oxidation in the bisque cycle is critical for this kind of
bloating.
I am using Goldart again, but in small quantities.
--
Louis Katz lkatz@falcon.tamucc.edu
Texas A&M University CC
6300 Ocean
CCTX 78412
(512) 994-5987
http://www2.tamucc.edu/LKATZ/LKATZ
Craig Martell on tue 10 feb 98
At 10:48 PM 2/8/98 EST, Brian wrote:
>----------------------------Original message----------------------------
>Hi everyone -
>I have a nasty bloating problem with this clay body :
>
>Lincoln Fireclay 100
>Cedar Heights Goldart 100
>OM #4 Ball clay 50
>Soda Feldspar 25
>Silica sand 5
>Yellow Ochre 2
>
>Does anyone know why this clay is bloating ?
Hello Brian:
Your firing schedule sounds reasonable, but how slow is slow? What kind of
temp rise per hour were you maintaining?
At about 900F. you are past the point where you will be oxidizing and
burning carbonates. Firing slow up to Quartz, which is about 1030F. is a
good idea. If you are oxidizing up to 06, and not forming any iron silicate
from too early reduction, that rules out any bloating there, but you might
want to break a piece or two and check for black core. Do you smell any
sulfur at 06? This should be mostly or totally eliminated in the bisque
firing. Do you detect any sulfur odor when your bisque is finishing? If
so, soak the bisque until the odor is completely gone, or bisque a bit higher.
The soda spar could be a problem. Soda will gas at high temp and this is
real bad in a clay body which is maturing, while the gasses are looking for
a way out. If there isn't a damn good reason for using soda spar as a flux,
I would reformulate the body with potash spar, which does not gas at high temp.
Overfiring a body can cause bloating too. How hot is the middle of the kiln
getting? You may need to test the body for absorbtion to see how vitreous
it is. If you are at, or near zero percent, you need to lower the firing
temp or adjust the spar to lower the maturation temp.
I hope something here is helpful, Craig Martell-Oregon
Lili Krakowski on wed 11 feb 98
All the advice given is really good and any bit of it may be the solution.
one more thing however. DRYING THE WARE. The few times I have
experienced bloating and black coring has been when I have speed dried
pots. Ain't that the truth? Ain't it always so? It has always been when
I've been up against a deadline and in a hurry. (There is a moral here
someplace but I don't have time to look, as I have to be somewhere in 1/2
an hour) What can happen is that as the finer particles of clay, or
sometimes, water soluble stuff in the clay, migrate to the surface if that
surface dries too fast, it seals same and does not allow the gases to
escape happily in the firign. To test for this "problem" take a typical
piece or two of the type that has given you this trouble, and dry it extra
slow inside a plastic bag. Remove from bag after a few days when the pot
is almost dry and let it finish drying "normally" see wothoppens. If this
is your "problem" you might add some more sand, or follow any of the other
advice. I mean: lowering the sulfur contents is always helpful...
Lili Krakowski
Lili Krakowski on wed 11 feb 98
All the advice given has been excellent, but let me add one more
suggestion. The only time I have experienced black coring and bloating
has been when I have speed dried the pots. (Ain't it always so?
when you're in a rush things go awry) The cause seems to be that fine
particles of clay brought to the surface in throwing, or water soluble
stuff in the body that are lifted to the surface as the water evaporates
tend to seal the "pores", which then prevent gases from escaping smoothly
in the fire. Sometimes YOU haven't done a thing, but, as it is winter, and
you may be heating your studio, that could be the cause: the heating of
the studio dries the air and speeds up the surface drying of your pots. To
test for this: put a typical pot of the type that has had this bloating
problem in a plastic bag, or in a styrofoam cooler and let it dry in
there. Remove from this dampbox after a few days when the outside is
still a little damp and let it dry normally. See wothoppens. I am aware
that we see lots of pictures of native potters all around the world drying
pots outdoors in the sun and wind. BUT their clay is NOT finely ground,
there are lots of big particles that make for good air/gas passages. You
simply may be having a problem with clay too finely ground....Maybe a
ltitle more sand? Good luck Lili Krakowski
JLHclay on sat 21 feb 98
I've experienced bloating with any extreme temp jump (more than 200 far. per
hour) at any phase of firing. Usually this happens when my pryromiter sp
sticks. I fire a gas updraft. Good luck Joy in Tucson
Dave Finkelnburg on tue 11 dec 01
Randy,
I'd put a lid on the recycle bucket! :-)
I think you've explained the problem. Overfiring can cause bloating,
and if you get it only in the recycled clay, it seems you are getting some
low-fire clay in the mix. More wedging, to thoroughly mix in the low-fire
clay, will help prevent the problem, and trapped air doesn't help a tight
clay body. Keeping the two clay bodies totally separate would help, it
seems to me.
Regards,
Dave Finkelnburg in southern Idaho, where today's snow is as light
as the spring seeds from a cottonwood tree
-----Original Message-----
From: Randy Peckham
>I use ^6 clay, and glazes, and never have a problem with bloating with
>"new" clay, fresh out of the bag. Sometimes sporadically I do have a
>problem with bloating with my recycled clay. I also have a low fire
>recycle bucket, and a 3 yr old who loves to play in the goopy buckets.
LJTCW@AOL.COM on wed 12 dec 01
I had a problem with^6 bloating clay this fall and tracked it down to the
clay itself. It bloated in the glaze firing regardless of how slow I
bisqued, to what cone I bisqued, or the schedule of the glaze firing.I
returned it to the supplier and replaced it with clay from someone else.
Louise
Louise Jenks
Turtle Clayworks
Cincinnati OH USA
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