Candise Flippin on wed 9 jan 02
Lesley and interested others,
I do not remember where I heard or saw this, probably someone on this list.
It sounds silly, but they refer to it as a technique to "wake up the clay".
After the slab roller, pick up the slab, mat and all, raise a few inches
from the surface and drop. IT WILL WAKE YOU UP TOO IF ITS A LARGE SLAB!
Technically, I believe this amounts to relieving the problem created by the
slab roller of the clay particles tending to line up in one direction
creating the stresses that result in cracks. I am sure one of our gurus
could clarify this.
In any event, I roll my slabs out slightly thicker than I wish them to be
after this final step. Then, "drop" them 3 times, carefully. (This is easy
with small ones, but does take a little finesse with large ones) It works
for me, and thank you to whoever suggested this if it was someone on this
list.
Thanks, Candise in Vista, North San Diego County
vince pitelka on fri 11 jan 02
Candise -
It is true that rolling slabs unidirectionally creates a linear grain
structure which can cause serious problems with warping or cracking. A flat
single-slab piece like a platter or bowl can warp badly. A vessel or
sculptural form made from multiple slab pieces can literally yank itself
apart from the slabs shrinking in different directions. When the slab comes
out of the slab roller I just roll it again with a rolling pin at 90 degrees
to equalize the grain structure. You do not even have to expand or thin the
slab with the rolling pin. If the slab is still stuck to the canvas or mat
on which it was rolled initially, it will not expand when you roll it with
the rolling pin.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
Candise Flippin on sat 12 jan 02
Vince,
I will gladly test this. I was taught to start very thick in the slab
roller and make several runs. Each time, flipping and turning the slab 90
degrees. Decreasing the amount you reduce the thickness towards the end. I
still found stresses unless something was done after the final run through
the slab roller. I asked Pete Pinnell about this at a workshop one time and
he said he knew of no way to prevent them. I know there are those who will
never use a slab roller and may even believe it is the devil's tool, but I'm
not giving mine up. It is a part of my process, and almost becomes a dance
sometimes. Enough of that. I will try the rolling pin at 90 degrees after
the last run on a test piece.
Thanks, Candise in Vista, North San Diego County
John Jensen on sun 13 jan 02
You do not even have to expand or thin the
slab with the rolling pin. If the slab is still stuck to the canvas or mat
on which it was rolled initially, it will not expand when you roll it with
the rolling pin.
Vince, how does that work? I can't see how you can affect the structure of
the clay without applying enough pressure to at least thin the clay a bit.
John Jensen, Mudbug Pottery
mudbug@toad.net www.Toadhouse.com
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