Craig Martell on fri 22 may 98
Hi:
It sounds like the bloating that you are getting in Oxidation could be
caused by too much bentonite, or too much of another type of
Montmorillonitic plasticizer that has been added to the body to make it more
workable.
Bodies that have a lot of bentonite added can bloat in Oxidation, but if
given enough exposure to reduction, no bloating is seen. You can also lower
the final firing temp to cone 9 Ox. This will sometimes get rid of the
bloats. I don't know how much reduction is enough, and I don't know for
sure if this is the problem. If you are getting bloats in Ox, and not Red,
it would lead me to think this is a definite possibility. You might try and
pry some info out of Laguna in regard to the problem.
regards, Craig Martell-Oregon
Alex, Aurora and Leah Solla on sat 23 may 98
Craig-
Now I am confused. How does bentonite contribute to bloating
in oxidation? Is it decomposing? I thought that it was made from
volcanic ash decay and had little organics in it. So what is causing the
bloating?
Alex in Utah where my carrots are up and chasing my lettuce and peas
At 08:20 AM 5/22/98 -0400, you wrote:
>----------------------------Original message----------------------------
>Hi:
>
>It sounds like the bloating that you are getting in Oxidation could be
>caused by too much bentonite, or too much of another type of
>Montmorillonitic plasticizer that has been added to the body to make it more
>workable.
>
>Bodies that have a lot of bentonite added can bloat in Oxidation, but if
>given enough exposure to reduction, no bloating is seen. You can also lower
>the final firing temp to cone 9 Ox. This will sometimes get rid of the
>bloats. I don't know how much reduction is enough, and I don't know for
>sure if this is the problem. If you are getting bloats in Ox, and not Red,
>it would lead me to think this is a definite possibility. You might try and
>pry some info out of Laguna in regard to the problem.
>
>regards, Craig Martell-Oregon
>
Craig Martell on sun 24 may 98
At 09:47 AM 5/23/98 EDT, Alex wrote:
>----------------------------Original message----------------------------
>Now I am confused. How does bentonite contribute to bloating
>in oxidation? Is it decomposing? I thought that it was made from
>volcanic ash decay and had little organics in it. So what is causing the
>bloating?
Hi:
I don't know the chemistry involved here. This has been determined from
experimentation.
Years ago, I used a commercial porcelain that bloated when I fired it to
flat cone 10. If I reduced the temp to cone 9, there was no bloating. I
was using an electric kiln and firing Ox. So I talked to the lab tech for
the clay company and he told me that this particular body was not suitable
for cone 10 Ox. because of the high bentonite content, which would cause it
to bloat, but if fired in reduction, it would not bloat at cone 10.
I then made some bentonite slabs and fired two at cone 10 Ox and two at cone
10 Red. The oxidation fired samples were very gassed and bloated and the
reduction fired ones showed at lot less. There was a little bit of gassing
in the reduction samples but not nearly as much as in the oxidation samples.
I don't know what is considered to be too much bentontite. This problem
only occurs when there is "too much". Of course, Laguna probably won't
reveal anything about the composition of the clay so you can't make any kind
of judgement about what's going on. Only intuitive guesses. I've thrown
about 500 pounds of b mix and found it to be so plastic that the drying was
uneven. A symptom of a montmorillonitic clay such as bentonite, is uneven
drying and cracking problems due to reduced capillary action. What you get
is bone dry edges and tops with sticky, cheese hard feet. This is what I
saw with b mix. Clays that are lower in montmorillonites and have more clay
that has a true kaolin lattice dry more evenly and crack less. Anyway, this
is what made me think of the possible high bentonite problem with b mix. It
could be something else though.
that's about it, Craig Martell-Oregon
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