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cmc gum in clay for plasticity?

updated mon 28 may 01

 

Marianne Lombardo on fri 25 may 01


For the past year, since I started working with pottery, I was never =
able to figure out what "plastic" clay should feel like. I've always =
felt that I'm having much more difficulty than I should have, when =
working on the wheel. I have tried throwing wet, less wet, dry, even =
drying the clay with a hair dryer. Everything was getting a bit =
discouraging.

Yesterday, I tried smearing my hands with some CMC Gum (already =
dissolved in water) while wedging some cone 6 porcelain clay (Tucker's =
MCM). What an amazing difference! The clay felt plastic and responsive =
and did what I wanted, for the first time. I was able to throw my pots =
with only 3 or 4 pulls, and happy with the result. For the first time I =
can see that I might have a chance at actually becoming a potter, =
eventually.

Of course I have still to put the handles on some mugs and a casserole =
dish, and bisque fire the lot. =20

Does anyone know if this is an acceptable practice? Will it cause any =
other problems during firing, or afterwards? Will it work wonders on my =
various Tucker's stoneware clays as well?

My assumption is that I should make sure the handles are treated in the =
same fashion to ensure even drying, because it does seem that the gum =
slows the drying time a little bit.

Marianne Lombardo
Omemee, Ontario, Canada
email: mlombardo@nexicom.net

iandol on sat 26 may 01


Dear Marianne Lombardo,

This is not a new idea. I thought it was published in one of the later =
editions of Glen Nelson's book as a way of providing better lubrication =
while throwing. I'm sure if you did a literature search you would find =
answers to your other questions.

Since CMC is some sort of carbohydrate, I can't foresee any real =
problems. It will just burn away when you fire. And if all the clay is =
treated the same way I would expect you handles and lugs to adhere =
without causing problems when you attach them.

The interesting thing to me is the way such minute amounts of some =
additives make such a marked difference to the way a clay will behave. =
That we have no way of explaining these things may be an indication of =
our ignorance of the clay water relationship.