Jonathan Kaplan on mon 14 oct 96
While all of the posts have indeed struck home with many correct answers to
this problem, what hs not been addressed is the spiral particle orientation
of the clay. If you use clay from a box or make your own clay and wedge or
pug it, the action of the auger as well as the action of wedging puts a
spiral, or directional orientation into the clay particle. If you throw
with this orientation, that is in its spiral orientation, the results are
"s" cracking in the center. It might be worthy to mention that this not
only occurs in thrown ware, but also in ware that is pressed or jiggered.
The trick is to orient the clay at 90 degrees to the spiral on the wheel
head, in the jigger mold, or in the press cavity. If you cut the pug into
sections, never orient the clay with the cut side down, or in line with the
shaft of the wheel. Always orient the clay with this cut side 90 degrees,
or at right angles to the wheel head.
Casting clay does nothave this problem as the particles orient themselves
parallel to the casting surface of the mold and tend to be more densely
packed than plastic clay.
Trust me, it works.
Jonathan
Jonathan Kaplan
Ceramic Design Group Ltd./Production Services
PO Box 775112
Steamboat Springs CO 80477
(970) 879-9139*voice and fax
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