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did i sell broken mugs?

updated tue 3 nov 98


Michael Banks on mon 2 nov 98

Hello Naama,

I must concur with Craig Martell. It is likely that your cracking problem
is excessive cristobalite in the body and more specifically, cristobalite of
a particular size distribution. Additions of feldspar may or may not help.
Craig is correct, it is likely that a lot of quartz is not participating in
fusion reactions in the body. You must take this up with your clay
supplier as it is his/her problem. I suggest changing clays because this
problem can be very insidious, leading to cracking of your products months
and years later. This can seriously undermine your reputation.

I don't have any truck with the view that mugs need to be pre-warmed to
survive the shock of boiling water. Any clay/body that can't stand this
sort of use, in this day and age, is fundamentally too weak for domestic

Michael Banks
Nelson, NZ