iandol on wed 2 oct 02
Dear Heather,
This is an interesting phenomenon which seems to crop up from time to =
time. I was first asked about it more than twenty years ago.
It is partly a result of what the outer hand is doing to support the =
clay and partly a function of the qualities of your clay.
As you spread the base out from the inside it has to be allowed to move =
carrying the wall you are creating towards the edge of the wheel. But if =
your clay is a little stiffer than usual, or you exert a strong inward =
force with your outer hand, and the adhesion of the clay on the outside =
is strong to the wheelhead your clay will start to fold and move in the =
only direction which gives it freedom. this is upwards, Eventually, the =
seal between the wheelhead and the clay breaks down and an annular =
cavity forms.
I think the solution is to use softer clay and to make the final coning =
pass bring your clay to the base diameter you require.
I know a potter who took this problem to a Clay conference and tried to =
find a solution form the experts who were given the performances. None =
were able to help her.
I hope this provides a solution for you .
Best regards,
Ivor Lewis, Redhill, South Australia
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