Ron Roy on wed 26 oct 11
Hi Url,
That glaze has a rather ideal expansion rate so I would not expect
either crazing or shivering on most clay bodies.
Are you saying this only happens on that clay body - how long have you
used that clay?
Better break a bowl and tell us if the clay is thicker where the
crazing is happening.
I'm Leaving in a few days on a two week trip Url - be quick and I'll
do a few variations of the glaze to see if changes there will help.
RR
Quoting Url Krueger :
> My standard thrown kitchen mixing bowls are
> showing crazing about a week after I take them
> from the kiln.
>
> These bowls have not been used yet and therefore
> have not been submersed in water. Any water
> take up would just be from humidity in the air.
>
> The cracks are on the inside only and start out
> in a circular pattern like a bullseye just outside
> of where the foot ring is. Eventually they progress
> across the bottom and some up the insides, but only
> a little ways. I don't see any crazing on the outside
> of the bowl at all or on the inside near the rim.
>
> My question is, is this just a simple glaze fit problem
> or is it a process problem. In other words, is there
> something I'm doing mechanically or in the kiln that
> is causing this, or do I need to reformulate the glaze
> or clay body.
>
> I'm using Georgies White Salmon (CC529) clay
> which is described in their catalog as "Increasingly
> popular for its friendly ways, White Salmon is a
> beautiful tight body and a kissing cousin of porcelain.
> A good choice when you're after great color
> performance! Shrinks 13% in firing.
> (Sample fired in oxidation at cone 6.)"
>
> The glaze is Clear Glossy Liner from Mastering
> Cone 6 Glazes.
>
> These bowls have been fired in an electric kiln to
> 1200C with a 20 minute hold at top temperature and
> slow cooled. Sorry, I don't have the actual program
> in front of me. The problem is not from just one
> kiln load but so far from three different runs.
>
> Any ideas/suggestions?
>
> Thanks.
>
> Frustrated Earl
> oregon, usa
>
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