Ron Roy on tue 28 feb 06
Best to explain what kind of clay - any iron for instance?
If stoneware clays are not formulated properly they can develope
cristobalite - expecially in solw fired and slow cooled situations above
1100C
Pter Sohgen wrote an article about this in Studio Potter volume 28 #1.
If you would like me to test some of that clay and would be willing to
prepare a sample (easy to do) let me know and I will run it through my
dilatometer.
There can also be a problem if the liner glazes has too low an expansion -
and if there is cristobalite present the problem is more likely.
I may be able to draw some conclusions if I analize your glaze.
Sounds like those pots could be ready to break - take care.
RR
>I finally got a chance to use some casseroles I made for cooking this
>week. There were both glazed, ? 10 fired, Sheffield stoneware
>claybodies. They are both realtively thick walled pieces.
>
>I was told when they were fired (wood and salt kiln) to be careful to
>actually use them for baking as even though they were fired to ? 10, at
>lower temps the thermal expansion rates could cause them to crack.
>
>While cooking with them this past week I used them in a 400? oven. I
>distinctly heard some loud "Tinks" from both pieces but neither seems to
>have cracked, neither the body nor the glaze. I did allow them to cool
>slowly.
>
>Any advice on to what's happening here?
>
>
>Thanks, Rob
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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