being@COMCAST.NET on mon 1 jul 02
I have been having a pretty consistent problem in bisque firing a commercial raku clay body. It seems that, even after waiting for several weeks between throwing and firing, my pieces are cracking in the bisque kiln. The interesting thing is that they all seem to fail in the same or quite similar fashion...specifically, the very bottom of the piece (maybe the bottom eighth inch or so) will crack completely off. Some pieces are more damaged than that, but most of the damage includes this bottom falling off thing.
I bisque fire in an electric kiln, usually to a cone 05, and I have been throwing on a Randall kick wheel using plaster bats. I tend to leave the pieces on the bats until they dry sufficiently to lift them off with no cutting, and I kind of wonder if that might have something to do with the problem.
Cheryl Hoffman on tue 2 jul 02
In a message dated 7/1/02 8:00:21 PM Pacific Daylight Time, being@COMCAST.NET
writes:
> > this bottom falling off thing>...> wheel using plaster bats. I tend to leave the pieces on the bats until
> they dry sufficiently to lift them off with no cutting, and I kind of
> wonder if that might have something to do with the problem>
All my pots are thrown on a Randall with plaster bats and I let them pop off
by themselves. I've never had that type of crack happen. I checked with a
friend that uses the same method and she has never had that type of crack
either. The community college where I took classes also uses the same
method...so I don't think it's the Randall/plaster bat thing cracking your
pots. I'm sure the Gurus can help you figure this out.
Cher Hoffman OT: Can I vent? Received my terrific potter poster today
(Thank you, Hannah). The mailer tube was longer than my mailbox so the
sh**-for-brains mailman BENDS THE TUBE IN HALF! G-r-r-r-r-r. I'll try
ironing the poster to see if I can get some of the wrinkles out.
william schran on wed 3 jul 02
Potter wrote: they all seem to fail in the same or quite similar
fashion...specifically, the very bottom of the piece (maybe the
bottom eighth inch or so) will crack completely off.
Works were thrown and allowed to dry on plaster bats, then popped
off. Even though you're waiting a long time to bisque fire, the
bottoms of the pots may still be damp, especially if they've been
left on the bats. I assume you're not trimming them so the bottoms
could be thicker than you think. try removing them from bats as soon
as possible after drying and letting dry a few more days upside down
to even out the drying.
Bill
Cheryl Hoffman on thu 4 jul 02
In a message dated 7/1/02 8:00:21 PM Pacific Daylight Time, being@COMCAST.NET
writes:
> I tend to leave the pieces on the bats until they dry sufficiently to lift
> them off with no cutting, and I kind of wonder if that might have something
> to do with the problem.
>
Hey there,
In my earlier reply to you, I forgot to mention a very important part
of using plaster bats, as Bill pointed out. I always remove the pots from
the plaster bats ASAP and check the bottom thickness (by tapping...you get to
know the sound). If the pot bottom is too thick, I let it dry for a bit with
the bottom up, trim, and always dry for the first day on an absorbent surface
(dry wall boards) with the bottom up. I flip them over the next day on
another (dry) board. I continue this until the pot doesn't feel cool against
my cheek (Thank you, Lorinfla, for these tips).
Hope this helps, Cher H.
Tom Desio on thu 4 jul 02
Thanks everyone for the suggestions on my bisque-ware problem. From now on
I plan to: remove the pieces from the plaster bats much sooner, make sure
that the bottoms aren't too thick in relation to the sides; make certain
that the bottoms are completely dry; not use that same batch of clay again;
pay my taxes on time; floss every day; and be nice to the elderly and
infirm. Amen.
Tom
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