Clay Times Back Issues Vol. 4 Issue 14 • Jan/Feb 1998 | Page 15

stresses of shrinkage had affected my
work, sometimes with the appearance of cracks. I wondered, what
would happen with larger work?
I knew working large was going
to take a long time. I wouldn’t be
making a figure that took a few days
to create. What about the clay’s ability to work along with me? Would I
get unwanted fatigue cracks from
working too long? Clay that develops these cracks is often referred to
as being “short”, perhaps because it
has a short working time. In
exchange for the short working time,
however, the clay artist gains the
advantage of less shrinkage.
Unfortunately, most “plastic” clays
have a higher shrinkage rate. The
clay I had found was extremely plastic and yet the data sheet listed a
maximum shrinkage of nine percent
for both drying and firing. I thought
it was worth a try. Happily, I’ve
found the clay to have less shrinkage
than the amount advertised. The
shrinkage has always been less than
seven percent for both the drying
and the firing. This clay loses its size
at the leather-hard stage. In the firing
it loses very little—about one percent.

STRENGTH
Some of the low-fire terra cottas
I’d used in the past were rather soft
and easy to chip or break. I knew I
would be returning to the U.S. and
wondered how my new ideas for
sculpture would withstand an overseas move. There’s also the question
of hail for an outdoor piece: how
would this new clay survive oneinch pieces of ice?
The clay I use can be fired up to
cone 12, but I like cone 9 or 10. It is a
high-firing, chip-resistant material.
There are other important aspects of
strength, too.
When building large, it is important for the clay to have wet strength.
Then there is strength at the leatherhard stage and after it is dry, the
green strength. This became crucial
to me when, early on, I was moving
my pieces in vans and trucks to kilns

JANUARY/FEBRUARY 1998

large enough for the firing. I once
moved a wet piece in the back of a
van. Laying down, her large cavity
didn’t have any inside support. At
that time she was just a torso and
weighed about 140 pounds. I truly
didn’t think she could survive the
move, but when she was lifted out
and placed upright, she was perfect:
her body had not lost its shape! So I
continued building on that piece.
Then it was moved twice again, in a
green state—all 300 pounds of her.
Next, we lifted her into a kiln. This
clay definitely has strength, but I
have gray hair anyway!

Note how the clay builds up on the fingers, a sign of
stickiness, or plasticity.

WARPING
Warping is less of a problem, I
think, when working large. The
weight of the clay itself helps the
sculpture to keep its form. I did test
my clay for its tendency to warp. It
didn’t!

The trolley (roll-around work table) used for building
large sculpture has extra-large wheels for durability.

WEDGING AND STORAGE
I don’t wedge my clay to eliminate air bubbles. The problem for
potters of having air bubbles show
up and deform their vessel while
throwing is not a problem with the
work I do. I think it must be an old
wives’ tale that an air bubble is going
to explode a piece in the kiln firing.
An air bubble could cause the wall to
be thin at that place and a crack
could develop, but it’s because of the
thinness of the clay, not the air
behind it. In 10 years of building my
large figures, I have never had a
problem with air bubbles and I'm
quite sure all the air bubbles were
not eliminated from my work. I
wedge the clay for uniformity. The
sedimentary characteristics of clay
can cause a sinking of particles. I
have seen clay come apart in the firing in a way that indicates a layer.
The piece will fit back perfectly to
where it fell off, so why did it simply
fall off? It probably wasn’t wedged
well enough.

PVC pipe placed under the kiln shelf acts as roller to
slide sculpture (built on shelf) directly into kiln.

continued on next page
The trolley/PVC/kiln shelf work system makes loading of heavy sculpture easy enough for one person
to do alone.

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