iandol on wed 27 aug 03
Dear Chris Campbell,
Why should you be experiencing slumping and how does Grog influence the =
behaviour of clay? Big questions which need more information to get =
answers which might please you.
First, I would ask if you are maturing your clay? If you are firing at =
the low end of the recommended range it may not yet be mature. Is it =
translucent?
Second, How much do you know about your clay? What is its composition =
and which additives are used to plasticise it?
Third point. I'm not sure all grogs would alleviate the problem. I have =
difficulty accepting some of the claims made for incorporating Any grog =
into a body mixture. But Molochite might help since it is fired to a =
temperature well above usual firing temperatures.=20
Now it sounds as though you are having difficulty with flanged plates, =
possibly handles and spouts as well. If so, you have to allow for =
pyroplasticity during the forming stage. Leave your flanges with a =
steeper angle and give them a tapered profile so clay at the outer rim =
is thinner than that at the root of the well to reduce cantilevered =
stress. Same with spouts.
I don't think there are easy answers on this one.
Best regards,
Ivor Lewis, Redhill, South Australia
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