Ivor and Olive Lewis on mon 12 nov 07
Dear Michael Wendt,
I was reviewing some notes I wrote earlier in the year about the =
influencing the degree of plasticity.
Recalling that Clay can behave like an Ion Exchange Resin I penned a =
note to the effect that it is possible to substitute Calcium Ions for =
Sodium and Hydrogen Ions. This has the effect of making a plastic clay =
short and prone to seemingly brittle fracture. This can occur when clay =
is wedged or kneaded on a bench surfaced with potters plaster. Although =
very little water is adsorbed from the clay into the plaster there is =
sufficient to dissolve some of the Calcium sulphate. This would be =
picked up from the paster surface and distributed through the clay as it =
is worked.
The effect would be to increase the force needed to deform the clay as =
it was being kneaded.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Michael Wendt on mon 12 nov 07
Ivor,
That cannot be the reason.
I wedge on a plywood table
covered with wet canvas.
Also, the wet canvas adds water
rather than removing it so
the stiffness I measured is
resistance to deformation.
The clay remains very plastic
in that it does not crack any
more than usual on bending.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave.
Lewiston, Id 83501
U.S.A.
208-746-3724
wendtpot@lewiston.com
http://www.wendtpottery.com
http://UniquePorcelainDesigns.com
Ivor wrote:
Dear Michael Wendt,
I was reviewing some notes I wrote earlier in the year
about the influencing the degree of plasticity.
Recalling that Clay can behave like an Ion Exchange
Resin I penned a note to the effect that it is possible
to substitute Calcium Ions for Sodium and Hydrogen
Ions. This has the effect of making a plastic clay
short and prone to seemingly brittle fracture. This can
occur when clay is wedged or kneaded on a bench
surfaced with potters plaster. Although very little
water is adsorbed from the clay into the plaster there
is sufficient to dissolve some of the Calcium sulphate.
This would be picked up from the paster surface and
distributed through the clay as it is worked.
The effect would be to increase the force needed to
deform the clay as it was being kneaded.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ivor and Olive Lewis on tue 13 nov 07
Dear Michael Wendt,
I agree. Under the circumstances you now describe the Ion Exchange idea =
would not be appropriate. But your experience does not invalidate that =
reason.
Perhaps you should read Grim. His descriptions of clays and their =
behaviours is streets ahead of any other text, Ralph E. Grim, "Clay =
Mineralogy", McGraw Hill. He also wrote "Applied Clay Mineralogy".
Interesting fact about Water. It can be regarded as an alcohol, the root =
member of a homologous series H-OH, CH3-OH, C2H5-OH.....
Best regards,
Ivor
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