Bob Pulley on sat 4 oct 97
I've been potting for over 25 years and have mixed my own clay most of the
time and have never had this experience before. A batch of stoneware is
thixotropic, it is weird, weird, weird. It seems plastic. sticky, and
punky all at the same time. It has no strength when thrown. It reminds me
of the trick with corn starch where you mix it into a paste that breaks
when moved rapidly, but acts like a liquid when shook back and forth in the
hand. My formula is in the studio and I am too lazy to go get it unless
one of you technicians thinks the formula is critical to this question. I
have mixed the same clay body several times before and ,though it is
nothing special, I have never had this problem before.
Something in the water?
Killer bacteria?
A mismeasurement?
What do you think?
Robert Pulley
bpulley@hsonline.net
Richard Burkett on mon 6 oct 97
Bob Pulley asks:
>I have mixed the same clay body several times before and ,though it is
>nothing special, I have never had this problem before.
>Something in the water?
>Killer bacteria?
>A mismeasurement?
>What do you think?
Let me guess, you made this clay with a new batch of nepheline syenite? Or
soda feldspar? Or maybe even a potash spar?
Some materials can release substantial amounts of alkali (sodium ions
primarily being the culprit), thus defloccuting the clay. I had a grad who
tried to make a cone 3 white clay body and mixed his clay to perfect
stiffness, only to find the next day it was nearly liquid slip. You can
temporarily negate this by adding vinegar or a similar mild acid to the
clay, but it will eventually come back. Some spars (and occasionally
frits) leach alkalies more or less, so you may have to test a few to find
one that fluxes the clay sufficiently, but doesn't deflocculate your clay.
Richard
Richard Burkett - School of Art, SDSU, San Diego, CA 92182-4805
E-mail: richard.burkett@sdsu.edu <-> Voice mail: (619) 594-6201
Home Page: http://rohan.sdsu.edu/dept/rburkett/www/burkett.html
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