Reid Harvey on sat 28 nov 98
Okay Gang,
Since returning to Africa in '94 it's my first time trying to
deflocculate a slip body. First time ever to deflocculate 'natural'
materials, not store bought ones. Can anyone offer some ideas? I am
thinking there may be soluble materials in my body.
I did come up with a deflocculated slip, however got carried away and
ended up with 60% water, much too much. Also my deflocculent (a mix of
Darvan 7 and sodium silicate) is 1.5%, also on the high end. This last
is what tipped me off I may have some soluble materials interfering.
My body is 75% kaolin, 15 plastic clay and 10 bottle glass. I screen
everything to 150 mesh, and hope that's adequate.
I process my clay with excess water and screen out coarse materials,
then pour the 'clay water' into a plastic burlap bag to remove excess
water. I would hope soluble materials would be washed away with this
step, but am wondering if it may be advisable to use additional water in
hopes of removing more of what's soluble. Louis Katz suggested washing
bottle glass and I will do this as well.
I guess it may seem strange to work with natural materials, that added
mystique, only to make readily replicable ware. (I use molds, almost
exclusively.) Kind of a contradiction to some. But here we have little
choice.
Thanks.
Reid Harvey
Abidjan
Louis Katz on sun 29 nov 98
Hi Reid,
If your bottle glass slurry leaves your hands feeling soapy it has lots of
soluble material. I would be surprised if this wasn't the case.
If I were having trouble defloculating without the bottle glass, I might
try washing the clay, but I would probably suspect the water. I would also
try adding a small amount of Barium Carbonate .1 percent unless you know
you have a problem with scumming on non slipcast ware.
What about adding some non-plastics. Is talc, feldspar, or flint available?
Rather than mixing the deflocculants first , I would under deflocculate
with sodium silicate and touch it up with Darvan, a little dab will do ya.
Not as experienced in defloculating as I would like to be, but...
Louis
--
Louis Katz
lkatz@falcon.tamucc.edu
NCECA Director At Large
Texas A&M-CC Division of Visual and Performing Arts Webmaster (512)
994-5987
Michael Banks on sun 29 nov 98
Gidday Reid,
Natural salts present in dug clay can commonly stuff-up the deflocculation
of them for casting slips. I commonly encounter this problem here (where we
make natural terracotta slips etc). The best remedy is to add a little
barium carbonate (yes, the dreaded barium). Add just enough in small
increments to counter the salts, which are acting as flocculants and
"fighting" the sodium silicate.
Barium carbonate converts naturally occurring sulphates to the insoluble
barium sulphate, thus removing them from the slip by precipitation. So if
you only add enough barium carb to wipe out the salts, there should not be
much left to present a health hazard.
Gypsum (hydrated calcium sulphate) is the most common culprit interfering
with deflocculents, but unfortunately I've found that no amount of washing
removes it from the clay. I've even found that some highly refined
commercial kaolins contain appreciable sulphate contaminants, in the
so-called developed world.
Cheers,
Michael
in Nelson, New Zealand
mjbanks@clear.net.nz
-----Original Message-----
>Okay Gang,
>
>Since returning to Africa in '94 it's my first time trying to
>deflocculate a slip body. First time ever to deflocculate 'natural'
>materials, not store bought ones. Can anyone offer some ideas? I am
>thinking there may be soluble materials in my body.
>
>I did come up with a deflocculated slip, however got carried away and
>ended up with 60% water, much too much. Also my deflocculent (a mix of
>Darvan 7 and sodium silicate) is 1.5%, also on the high end. This last
>is what tipped me off I may have some soluble materials interfering.
>
>My body is 75% kaolin, 15 plastic clay and 10 bottle glass. I screen
>everything to 150 mesh, and hope that's adequate.
>
>I process my clay with excess water and screen out coarse materials,
>then pour the 'clay water' into a plastic burlap bag to remove excess
>water. I would hope soluble materials would be washed away with this
>step, but am wondering if it may be advisable to use additional water in
>hopes of removing more of what's soluble. Louis Katz suggested washing
>bottle glass and I will do this as well.
>
>I guess it may seem strange to work with natural materials, that added
>mystique, only to make readily replicable ware. (I use molds, almost
>exclusively.) Kind of a contradiction to some. But here we have little
>choice.
>
>Thanks.
>Reid Harvey
>Abidjan
>
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