Floating Clay - Ceramic Arts Daily

Frogs, lily pads and flowers, to 8 inches (20 centimeters) in diameter, handbuilt, colored Floating Clay, fired to Cone 8.
Floating Clay
by Randolph Sill
I was studying ceramics recently in Shigaraki, Japan, a mountain
pottery village about two hours from Kyoto. While learning methods
of contemporary ceramic sculpture, as well as traditional
Japanese pottery techniques, I conceived of a ceramic sculpture
that would be installed in the ponds of Togeinomori, the Shigaraki
Ceramic Cultural Park, on the outskirts of town. I wanted to
make the sculpture float on water, an endeavor doomed to be
difficult. Wouldn’t it be cool, though, to have the sculpture meander
around the ponds and go wherever the winds directed? Pedestals
can be so confining!
I initially imagined using slabs to create sealed forms that
could float on the surface of the water. I would leave a small hole,
through which expanding air could escape during the firing, and
then plug it with wax or silicone after firing. Although this
technique seemed feasible on paper, I imagined it would be quite
difficult for the large scale I intended. My second inclination was
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58
The cross-section of a piece of fired Floating Clay shows the
bubbles that are trapped when silicon carbide turns to gas.

to use slabs again, but make a five-sided
“cap” that would be inverted on the surface
of the water and trap air underneath. For
insurance, I could float the cap with buoyant
materials like foam blocks or inflated
inner tubes: not an elegant or enduring
solution. I might have tried it, and it might
have worked, had I not heard the legend of
the mysterious floating clay.
In Japan, the government supports their
ceramists to such a degree that it builds and
operates glaze- and clay-testing facilities in
each prefecture. According to the story, back
in the 1960s, government ceramics scientists
were experimenting with various additives
for clay and accidentally discovered
that it was possible to make clay float. Recently,
a scientist at the Shigaraki facility
had reopened the file on this baffling paradox
and had been performing experiments
in the hope of finding a viable commercial
application. A minuscule amount of silicon carbide is added to a
uniquely composed clay body. The silicon carbide turns into a gas
during the firing, which is encapsulated within the clay in the
form of bubbles. Each bubble is completely sealed so the gas can’t
escape and no water can permeate the clay.
The final product is confounding. It is deceptively light and
has a waferlike consistency. It is lighter than soft kiln brick or
pumice. When cut or broken, the interior reveals the gaseous
bubbles and looks like baked bread.
Alas, floating clay is challenging to work with. Even with
adding methyl cellulose and toilet-paper pulp, the clay body is
short and has very little elasticity. Despite this drawback, it is not
necessary to slip and score when working with floating clay, as the
parts will fuse together while firing. You can make fairly thick
objects as well. If the silicon carbide is not evenly mixed into the
clay, uneven distortion can occur. If the clay is well mixed, the
final product will “rise” in the kiln and expand in a uniform
fashion, but it is not particularly strong or resistant to wear. On
the other hand, it doesn’t retain heat, it won’t crack when frozen
and it floats on water!
Mixing Floating Clay
One of the greatest challenges I encountered was in getting the
active ingredient, silicon carbide (SiC), evenly distributed through-
The Shigaraki Ceramic Cultural Park provides space for artists, as well as research and exhibition facilities.
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59
out the clay body. This is partly due to the fact that the SiC
comprises only 0.5% of the total dry weight of the clay body. I
mixed the clay by first mixing all dry ingredients together, minus
the SiC. Then I took 10% of the dry-mixed ingredients and
added the SiC. This was shaken vigorously in a plastic bag for a
few minutes, then ball milled for approximately 20 minutes.
Next, I added more dry ingredients (about 40% total weight) and
placed that in a dough mixer for 20 minutes. Because the clay is
composed of 25% water, I added all of the water to only 40% of
the dry ingredients, made a slurry in the dough mixer and let it
mix for 10 minutes. I then added in the remaining dry ingredients
and mixed thoroughly.
Forming
Because of the absurdly high feldspar content, Floating Clay is
very short. It has almost no elasticity and is difficult to dry
without cracking. I remedied this problem somewhat by adding
one or more of the following ingredients: methyl cellulose (a
weak, nontoxic adhesive), Biopoly (an organic additive), and
toilet-paper pulp for strength (one roll of toilet paper for every 10
kilograms of wet clay).
Floating Clay can be thrown, but the forms I threw slumped a
lot in the kiln. Perhaps decreasing the silicon carbide, or firing to
a slightly cooler temperature, might have helped. Give it a try!
PHOTOS: SHINJI OTANI

Finished sculptures made of colored Floating Clay, fired to Cone 8,
by Randolph Sill, Seattle, Washington.
Firing
This is important. Protect your kiln in the following two
ways: First, recognize that floating clay distorts and expands in
the kiln. Leave a lot of extra space around your pieces. I can’t
tell you how much they will rise, as that depends on the total
quantity of clay that is fired. For example, a 6-inch-diameter,
1-inch-tall cookie may only grow to be 7 inches in diameter. A
6-inch-diameter, 4-inch-tall cookie may end up growing to 9
inches in diameter.
Second, coat the kiln shelves with a thick layer of alumina
hydrate in powder form as well as kiln wash. Sift it right onto
the shelf. It should be about ⅛ inch thick. This will not only
prevent the clay from sticking to the shelves, it will allow the
clay to grow horizontally with as little friction against the kiln
shelf as possible. Don’t skimp on the alumina hydrate, as you
can reuse it in subsequent firings.
If you have any breakthrough discoveries, or if you need
more recipes or information, please contact Randolph Sill
through www.madpotter.com.
Ceramics Monthly February 2004
60
recipes
White Floating Clay Base
(Cone 8)
Hata Feldspar .................................. 80.0 %
Motoyama Clay ............................... 10.0
New Zealand Kaolin ........................ 10.0
100.0 %
Add: Methyl Cellulose ..................... 1.0%
Silicon Carbide ........................ 0.5 %
This base recipe has low distortion, but is less
buoyant than the pink base.
Pink Floating Clay Base
(Cone 8)
Hata Feldspar .................................. 50.0 %
Nissan Feldspar ............................... 30.0
Bentonite ........................................ 5.0
Motoyama Clay ............................... 10.0
New Zealand Kaolin ........................ 5.0
100.0 %
Add: Methyl Cellulose ..................... 1.0%
Silicon Carbide ........................ 0.5 %
The pink color of this base is a bit muted. It
has more distortion upon firing and, as a
result, is more buoyant than the white base.
Substitutions for Motoyama clay should contain
less than 20% sand.
Colorants for Floating Clay
Royal Blue
Cobalt Oxide ....................... 0.5–1.0 %
Brilliant Blue
Blue Mason Stain ...................... 3.0%
Bright Yellow
Vanadium Oxide ....................... 3.0%
Light Green
Vanadium Oxide ....................... 3.0%
Chrome Oxide .......................... 0.5%
Dark Green
Chrome Oxide .................... 0.5–1.0 %
Mint Green
Copper Carbonate .................... 1.0%
Percentages based on weight of wet clay.
Other colors can be tested using stains at 3%
as a starting point.
Hata Feldspar
K2O ................................................... 30%
Na2O ................................................. 50
SiO2 ................................................... 20
100 %
Nissan 7 Feldspar
K2O ................................................... 30%
Na2O ................................................. 30
SiO2 ................................................... 39
Fe O ................................................. 1
2 3
100 %