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double walled bowls cracking in firing

updated thu 8 may 03

 

Eliza McInnes on wed 7 may 03


I have been making double walled bowls since the beginning of the year and
have received and order for a set of three, the largest being 400mm across
the top and 250mm in hight.

I have made a couple with ten kg of E W clay thrown upsidedown, the only
problem is they have cracked in a very slow firing to ^05.
They were fully dried and I tried firing upsidedown

The crack looks like a dunt you know the ones that spiral around, yet I
unpacked the kiln cold,


is it because of uneven wall thickness, the hole in the base being too small
I just used a needle, I need to rethink the clay body, I need to dry them
slower or have i stressed the clay out in the closing off or is it somthing
else?

I just dont know

any help would be greatly appreciated.

Eliza
Sydney
Australia