Paul on sun 6 oct 02
Hello glaze experts!
The following glaze, fired to cone 11, seems to be the cause of some rim
cracks along the inside of pots. I pour this glaze on the inside and spray
two different glazes along the outside rim and the bottom of the pot. I have
had to unload the kiln "with gloves" lately due to time constraints but this
has not cracked any other of the pots in the same way. so is it possible
that a certain type of glaze would cause cracks like this? The recipe is as
follows:
Dolomite 12.00
Strontium 6.00
Whiting 8.00.
Neph Sy 37.00
EPK 2.00
Flint 35.00
Copper carb 2.00
Rutile 5.00
Has anyone had a similar experience, or have any suggestions?
Thanks,
Paul
Falmouth KY
Paul Herman on sun 6 oct 02
Paul,
Sometimes, if you use glazes of differing thermal expansion on the
inside and outside of a pot (ie. one that crazes and the other under
compression), the forces are just too much for the claybody, and it
cracks. This also happens sometimes if only the inside is glazed and the
outside is bare.
One particular glaze that has caused trouble in my kilns is a shino that
has a lot of spodumene in it. My firing partner Joe Winter used it on
the outside of some tall (2 foot) vases last firing and they split open
while cooling. We heard them tearing open in there about 300F. Lithium =
low expansion. A really pretty glaze too, wouldn't you know it?
Sounds like a possible "bad" combination.
Best wishes,
Paul Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
potter@psln.com
----------
>From: Paul
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: rim cracks with this glaze...
>Date: Sun, Oct 6, 2002, 5:05 PM
>
> Hello glaze experts!
> The following glaze, fired to cone 11, seems to be the cause of some rim
> cracks along the inside of pots. I pour this glaze on the inside and spray
> two different glazes along the outside rim and the bottom of the pot. I have
> had to unload the kiln "with gloves" lately due to time constraints but this
> has not cracked any other of the pots in the same way. so is it possible
> that a certain type of glaze would cause cracks like this? The recipe is as
> follows:
> Dolomite 12.00
> Strontium 6.00
> Whiting 8.00.
> Neph Sy 37.00
> EPK 2.00
> Flint 35.00
> Copper carb 2.00
> Rutile 5.00
>
> Has anyone had a similar experience, or have any suggestions?
> Thanks,
> Paul
> Falmouth KY
Ron Roy on tue 8 oct 02
Hi Paul,
Nothing wrong with the expansion of this glaze - It is not low enough do be
a problem.
I need to know - are the cracks open or closed - is the glaze at the crack
sharp or melted?
hat glaze looks like it will settle like a rock - are you sure you are
getting it all mixed up properly befor applying it.
Tell us about the cracks before we all go off half cocked.
RR
>The following glaze, fired to cone 11, seems to be the cause of some rim
>cracks along the inside of pots. I pour this glaze on the inside and spray
>two different glazes along the outside rim and the bottom of the pot. I have
>had to unload the kiln "with gloves" lately due to time constraints but this
>has not cracked any other of the pots in the same way. so is it possible
>that a certain type of glaze would cause cracks like this? The recipe is as
>follows:
>Dolomite 12.00
>Strontium 6.00
>Whiting 8.00.
>Neph Sy 37.00
>EPK 2.00
>Flint 35.00
>Copper carb 2.00
>Rutile 5.00
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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