The Art of Polished Clay Balls

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.


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!


軽量藁土充填工法 Light Straw Clay Construction: Irwin A. and Robert D. Goodman Greenhouse at Spring Harbor

In April, 2015 I had the opportunity to participate in the construction of the Irwin A. and Robert D. Goodman Greenhouse at Spring Harbor Middle School in Madison, WI.
外壁は軽量藁土充填工法という工法でできました。Design Coalitionという環境建築設計事務所によって設計されました。デザイン・コアリションは20年前から軽量藁土充填工法を開発しています。The greenhouse features light straw clay walls built under the direction of Design Coalition, a sustainable and socially conscious architectural firm in Madison, WI. Design Coalition is a pioneer of light straw clay construction in North America and has been researching and designing with light straw clay for over 20 years.
The construction of the Irwin A. and Robert D. Goodman Greenhouse at Spring Harbor Middle School is led by middle school science teacher Dave Ropa. In addition to the use of natural building materials, the building will showcase a number of ecological features including rain water catchment and organic gardens.
The interior finish features Kiwado's NAGOMI Japanese lime plaster applied directly over an earthen plaster base coat.

下の写真が建設の記録で、ある写真がManderfield Video Productionsあるいはデビド・ロパ先生の厚意による写真です。
The following is a photographic exploration of the construction of the Irwin A. and Robert D. Goodman Greenhouse. Some photos are courtesy of Manderfield Video Productions and Dave Ropa.

基礎断熱 Insulated Foundation

Durisol Blocks made from cement and wood chips recycled from used pallets

木造 Timber structure

軽量藁土ミクサー Light straw clay mixer

Stomping light straw clay into formwork

Wooden spacers secure inside shuttering. As the wall is built, the spacing blocks are removed creating a monolithic light straw clay wall

Before applying the first coat of earth plaster, a clay slip is sprayed on the surface.
The base coat of plaster was applied in two days.

The first day the entire middle school took turns plastering.

What incredible energy and team work! Truly an inspiration.

The second day parents and community members continued plastering.

下塗の様子 Completed base coat of earth plaster

Generally a brown coat is applied before the finish coat. However, given a limited schedule, the interior finish was applied in 2.5 days. The interior finish features a traditional Japanese lime plaster. In Japan, lime plasters have been used to finish earthen walls for hundreds of years. The finish plaster was applied in two consecutive coats.

Kiwado's NAGOMI plaster consists of hydrated lime, recycled jute fibers and seaweed glue.

Textured wave pattern applied with brush.

Sun and moon truth windows exposing the light straw clay (right) and base coat of earthen plaster (left).

内装 Kiwado's NAGOMI lime plaster

外装 Wood siding on the exterior