Irv Knowlen on tue 26 jun 01
I'm interested in making very large, drapemold, cone 10 platters (wall
hangers) but fear they will slump when fired. Is their a clay body that
will work? or can they be reinforced with fiberglass somehow. It seems
that I read (some years ago) about one of our major ceramists making
large sculptural forms reinforced with fiberglass somehow. Fiberglass
fabric?
Irv k
Snail Scott on tue 26 jun 01
At 09:29 AM 6/26/01 -0500, you wrote:
fear they will slump when fired... I read...about...forms reinforced with
fiberglass somehow.
>Irv k
Fiber of many sorts, including fiberglass, nylon,
paper, rag, etc, can do wonders in reinforcing clay,
and is especially suited to slab work such as you
described. However...
The reinforcement is in the greenware phase only.
All of these fibers melt or burn out in firing.
I know of no fiber reinforcement process which
will benefit fired clay in any way. There have
been many suggestions of late on preventing
warping during firing, including ensuring level
shelves, sand on the shelf (to ease shrinkage
friction), and designing forms which are structurally
sturdy and self-supporting when reaching vitrification
temperatures. Fiber won't help, though.
Slab work seems more prone to slumping than thrown
work. I believe this is due in part to the less-
aligned and less-compressed particles in the typical
slab, when compared to an equivalent section of
thrown clay. 'Memory' may also play a role, especially
with porcelain, I believe. A thrown platter is often
thrown with a high rim which is flattened out and
stretched in the last phases of throwing, and the
clay remains in slight tension, which allows the clay
'memory' to aid the potter by returning it to a
slightly lifted position instead of flopping down. A
slab, by contrast, usually starts life as a flat thing,
later shaped (in your case) by draping on a mold. What
the clay particles 'remember' is their previous flatness,
when they were compressed into a slab by vigorous
rolling, not the comparatively mild modification of
being draped, which may place the concave-side particles
in slight compression while putting the convex-side
particles in tension. I personally believe that slab
work will slump less if it is well worked over in its
new position, realigning the particles as much as
possible.
-Snail
p.s. with regard to the term 'compression' and its kin:
let's not go there again, OK?
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