Last April I had the opportunity to visit Denise Duroux Thornton and Doug Hansmann of the Underhill House in Southwestern Wisconsin. Denise is a freelance writer and maintains an excellent blog about all things sustainable called Digging in the Driftless. Their home, the Underhill House, was built by Whole Trees Architecture. The Underhill House features a round stock timber frame, straw bale walls, an earthen plaster interior and lime plaster exterior, a living roof, and a solar hot water heater used to provide hot water and space heating.
Southern aspect for passive solar gain
Contrasting dark walnut earthen plaster and painted white round stock timbers
Potential use of natural tree limbs for diagonal bracing.
Interior stain glass window
Close up of stain glass window
Design around bathroom mirror compliments stain glass
Skip trowel earthen plaster finish
Round stock brings the room to life
Inexpensive light shades from Vietnam.
Denise, Doug, Kazuko and Kyle
Barn features an attached greenhouse.
Whole Trees Architecture
We also had the opportunity to visit Roald Gundersen, founder of Whole Trees Architecture, and were fortunate to be able to visiting the preparation of round stock timbers.
The art
of polished clay balls, known as hikaru
nendo dango or hikaru doro dango
in Japanese, first began in Japan in the 1980’s. Shinkichi Enomoto-san, a renowned
plasterer in Tokyo famous for his modern Otsu finish (polished earth-lime
plaster), is held as the originator of polished clay balls. Due to its simple
and beautiful nature, the art of polishing clay balls is becoming popular throughout
the world.
Polished
clay balls made from colored clays in Thailand
Polished
clay balls can range in size from balls too large to carry to balls as large as
one’s thumb, but generally the size of a tennis ball is the easiest to polish. ca.800mm diameter (Kyoto Plastering Institute)
ca. 200mm diameter (Toho-sangyo, Hiroshima)
ca. 50mm diameter (Toho-sangyo, Hiroshima)
ca. 20mm diameter
There
are two types of polished clay balls: (1) Genuine polished clay balls and (2)
earthen balls with a thin lime-earth plaster veneer. The process of polishing
both types of balls is explained below.
Genuine
polished clay balls (right) and lime-earth veneer (left)
The
first step in either method is preparing fine clay. In principle, the finer the
particles, the easier to polish. Ideally, wild clayey soils should be dried,
pulverized and sifted through 1mm or smaller sieve. Alternatively, wild clays
can be mixed with water into clay slurry and then strained through a 1mm or
smaller sieve to remove gravel and sand. Allow the fine clay to settle for 24
hours, gradually separating from the water. Once the water is clear, remove the
water with a shaku ladle, leaving a fine clay cream at the top of the sediment.
Sensei’s
collection of colored clays from around Japan
Polished
clay balls can also be made from commercially available clay, such as the
bagged clay sold at pottery supply stores, etc.
Genuine Polished Clay Balls
If
starting with dry, powdered clay, re-hydrate the clay in water. “Do what you
ought’a, add clay to wat’a”, was the advice I received from my first earth
building mentor, Gene Leone, in the US. That is, first add a small amount of
water to a bucket. Slowly sprinkle in the dry clay, allowing it to soak up the
water. Continue slowly adding clay until the soil comes to the surface of the
water and only dry clay is visible. Allow the clay to sit for at least 15
minutes before mixing. While soaking, the clay will become entirely saturated
through capillary action. Thoroughly mix ensuring even hydration. Slowly mix in
more dry powdered clay as needed to obtain a stiff enough consistency to make
clay balls with one’s hands. This method generally produces an accurate soil
hydration, but the ratio of soil and water will depend on the clay content of
the soil. The greater the clay content, the more water needed to rehydrate.
Hydrated
clayey soil formed into balls with one’s hands
Allow
the fresh clay balls to slowly dry in the shade. As the balls dry, softly roll
them in the palms of one’s hands, attempting to make them as round as possible.
As the
balls begin to stiffen, use a round sake cup or similar item to shape the balls
into spheres.
Clay
balls shaped with a spice jar and sitting on a soft sponge cushion
Very
expansive clays, like bentonite, will crack as they dry and are generally not
suitable for polished clay balls. Most other clayey soils can be used.
As the
ball dries more, transition from shaping to compressing. At this stage, one can
apply more pressure without the ball losing its shape. Use the sake cup to
compress the balls, removing inconsistences and making the surface smooth. Be careful
not to apply too much force or the balls will lose their shape.
Compression
As the
balls dry even more, it is time to begin polishing. If clay sticks to one’s
sake cup, it’s still too early for polishing. Once the balls have become hard,
but still contain sufficient moisture, more pressure can be applied with the
sake cup, polishing the surface. If the balls have dried too much, the sake cup
will scratch the surface rather than polish.
From
compression (right) to polishing (left) (Photo: Ryan Libre)
If the
ball is not perfectly spherical or there are areas not making proper contact, a
polishing stone can be used to polish those areas.
Tadelakt
polishing stone used to polish balls
When the
ball is too dry to polish with the sake cup, one’s hands can be used for the
final polishing. As the ball is rubbed in one’s hands a squeaking sound occurs.
Soft hands will ensure better results. The clay ball extremists will apply hand
lotion the night before and sleep with soft cotton gloves on to soften the
skin.
Final
polish by hand (Photo: Anna Wolfson Studios, Chicago, IL.)
Unlike
using a lime veneer, the balls do not require any treatment with oil or soap,
and should not lose their shine over time.
And if
you were ever wondering what happens when you drop a genuine polished clay
ball, one of mine found the floor during an earth quake.
Notice
the air pockets in the ball, left as water evaporates during drying
Earth-Lime Veneer Polished Balls
The core
of the earth-lime veneer balls can be produced similar to the process above.
However,
rather than a relatively pure clayey soil, a typical brown coat earth plaster
mix can be used to create the core. Use a sake cup or PVC pipe ring to shape
the balls into spheres.
Unlike
the genuine polished clay balls, the brown coat plaster mix cores can be
allowed to dry longer, and stiffen up significantly before final shaping. If
the balls have dried too much, simply dip them in water for a second to soften them.
The additional sand increases capillary action and allows the balls to be
reshaped easily. Once the balls are near perfectly round, allow them to thoroughly
dry.
Completely
dry brown coat plaster core
Preparing
the lime-earth plaster:
Sift
lime and color clay through a 1mm sieve. If color clay is unavailable, alkaline
resistant mineral pigments can be used. The proportion of lime to color clay or
lime to pigment is flexible. The greater the percentage of lime, the easier to
polish but weaker the color. To begin with, try 4:1 :: lime:color clay.
In
this case slaked quick lime cream and red soil from Okinawa were used
Mix dry
the lime and earth and then thoroughly mix with water to obtain a milkshake
consistency. This mix can be used as a thin lime-earth veneer, or the thin mix
can be further sifted through an 80 mesh screen to decrease particle size and
improve polishing.
Japanese
Plastering—Kiwado offers HIKARI lime plaster, a very fine dry powdered lime
plaster with improved workability for polishing.
Apply
the lime-clay plaster to the brown coat plaster core with a smooth plastic lid
as quickly and evenly as possible. When enough plaster has been applied to
ensure sufficient stiffness and moisture for compression, begin light
compression with a sake cup or smooth PVC pipe ring. If the plaster is too damp, drying can be hastened with a dry paper towel.
Use a paper towel to remove moisture and stiffen the lime-earth plaster before forming and compression.
Clean the cup or ring
regularly. As the veneer dries, more pressure can be applied. With sufficient
moisture present, the ball can be polished.
Polishing a lime-earth veneer over a brown coat earthen plaster core
Polishing
lime-earth veneer with cup
If the veneer is too dry, the cup
or PVC pipe ring will scratch the finish. At this
stage, a very small amount of olive oil or olive oil soap can be applied to
reduce friction and prolong polishing. The application of olive oil or olive
oil soap will also help the lime-earth veneer to maintain its shine over time.
A finished lime veneer without an oil or soap treatment may react with
humidity, bringing free lime to the surface and clouding the shine over time.
If kept in a relatively dry place with less humidity variation, an unprotected
lime veneer is less likely to lose its shine.
Lastly,
buff with a felt cloth.
Buffing
with felt
In
conclusion, I’m often asked:
“What’s
the purpose of polished clay balls?”
“What
can you use them for?”
“Why do
you make them?”
The
answer is, “They’re good for nothing… Isn’t this one beautiful?”
Six
people from as many countries enjoying the art of polishing clay balls!
