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: thermal shock w/ reduced clay

updated wed 30 may 01


iandol on mon 28 may 01

Dear Matt MacIntire,

This is an interesting problem, but I would not consider seeking a valid =
solution without a great deal more information about your clay and your =
testing method.

That said, my blind guess might be delayed dunting initiated by thermal =
shock if the boiling water is being poured on dead cold pottery. It may =
have nothing at all to do with the iron(2)oxide unless that material =
influenced one of the silica phase changes or the development of a =
greater proportion of a vitreous phase in a reducing atmosphere.=20

From the colours you describe then there is only a small proportion of =
iron oxide to begin with. It is possible that most of this goes into a =
solid solution. If this is the case, it may be evenly dispersed =
throughout the matured ceramic in either the vitreous or another phase =
and might not contribute to any form of crack initiation.=20

Perhaps having Ron Roy test a specimen may be more revealing.

One other question I would ask is, does this destructive effect happens =
when your pots are heated from cold in a cold oven or brought up from =
cold to boiling in a water bath?

Best regards,

Ivor Lewis. Redhill, South Australia