What Is Sado Mumyoi? Teapots of Natural Red Clay (Zhuni)
Sado Mumyoi is pottery made from red clay that is produced as a byproduct after gold is mined at the Aikawa Gold Mine on Sado Island.
What Is Sado Mumyoi?
Locally on Sado, this is called Zhuni, but at HOJO we collectively call the clays found on Sado red clay, or Mumyoi. Red clay is not a single type of clay. Some, such as Nosaka, are yellowish clays close to Yixing Zhuni, while others are red. It consists of various clays with different properties.
Sado red clay contains a large amount of iron. Unglazed pottery made by firing it at high temperatures is called Mumyoi.
During the Edo period, Sado prospered through the gold trade. It was also the place where Emperor Juntoku was exiled. Influenced strongly by Kyoto culture and, owing to its proximity to the continent, by Chinese culture transmitted through the Korean Peninsula, Sado developed a firm foundation as a cultural home for tea.
At that time, high-grade teaware meant Zisha teapots made in Yixing. Although this is little known today, wealthy tea enthusiasts and cultural figures considered owning a Yixing teapot a status symbol, the ultimate luxury permitted only to the rich. One person noticed that red clay from Sado's gold mine had properties remarkably similar to Yixing clay. This was the first Miura Jozan, whose lineage later produced a Living National Treasure. By studying Yixing clay, firing methods, and design, Miura Jozan established the foundation of present-day Mumyoi. These unglazed teapots with a rear-handle design, rare in Japan, were embraced by tea enthusiasts for the quality of tea they produced. Records state that the famous Katsu Kaishu also commissioned teaware from Miura Jozan.
Today, however, the number of artists producing unglazed teapots using only natural clay has fallen sharply. HOJO was among the first to introduce Mumyoi overseas. Since Yixing teapots naturally dominate the overseas market, Mumyoi is compared with them. We found that while traditionally made Mumyoi performs well among Japanese teaware, it falls far short of Yixing Zhuni teapots. With the cooperation of artists, HOJO examined clay types, whether and in what proportion to blend them, firing temperatures, and firing methods. In recent years, we have completed teaware that performs as well as, or better than, Yixing teapots.
1. What Is Zhuni?
When you visit a tea shop, you will invariably see red teapots. Because they are red, these teapots are commonly called Zhuni teapots. However, being red does not necessarily make a teapot Zhuni. In Japanese, the word "red" is used frequently, and all reddish shades are called red. In Chinese, however, different words are used for particular colors. Naturally, vermilion is not the same as red.
Vermilion is the color used by calligraphy teachers for corrections, the color of a ripe persimmon.
Zhuni (red clay of the Yixing type) is not vermilion in its raw state. In Yixing, raw clay that is red is generally called Hongni, and it turns red or slightly blackish red when fired.
Whether teaware turns red depends more on the firing method than on the clay. The following are HOJO's Mumyoi series. They use the same clay, but their fired colors are entirely different depending on the firing method.
Raw clay from Sado
2. Sado Red Clay
On Sado, each artist uses different clay and has their own mining location. Traditionally, Mumyoi has been made by blending two clays, red clay and yellow clay. Both are excavated near the Aikawa Gold Mine and contain very high levels of iron. Here, both are collectively called “red clay.”
Red clay
Nosaka clay
The red clay closely resembles Hongni, one of Yixing's Zisha clays, both in its raw color and in its fired color.
I once had a test piece fired using this clay at 100%, and its color became a slightly dark red.
The yellow clay is called Nosaka. It is a very plastic, fine-grained clay.
This clay has properties extremely close to what is called Zhuni in Yixing Zisha.
Because it is highly plastic, it can be thrown on a potter's wheel by itself, and when fired it becomes a bright, persimmon-like orange.
Even among red clays, properties differ by clay. Many are loose and sandy, with too little plasticity to be thrown on a wheel. For this reason, yellow clay with high plasticity is blended in at a certain ratio. Sado teapot artists create plasticity by mixing yellow clay into red clay. Mixing the two clays also makes them tighten during firing. As for the benefit of tightening during firing, it offers no particular advantage to the user or to the flavor of tea.
Curiously, each clay hardly tightens when fired alone. It may tighten when blended because the yellow clay permeates the red clay.
HOJO carries two types of clay.
Mumyoi (Red Clay + Yellow Clay)
This is a blend of red clay and yellow clay.
However, by bringing the proportion of red clay as close to 100% as possible, we bring out the performance of the red clay.
Since 100% red clay is too loose and sandy to throw on a wheel, we blend in the minimum amount of yellow clay.
At HOJO, we repeatedly conduct tastings and, together with the artist, study the type of red clay, blend ratio, and firing temperature. We make teaware under the optimum conditions based on the goal of improving the flavor of tea.
Below is a mining site for natural red clay lying beneath Sado Island.
Nosaka (100% Yellow Clay)
This is pottery made from 100% yellow clay.
It is 100% natural Zhuni from Japan.
This series has never been made on Sado, either now or in the past.
After repeated tastings at HOJO, we discovered that 100% Nosaka (yellow clay) delivers exceptional performance and succeeded in bringing it to market.
Even clay called Nosaka varies depending on where it is mined. Because flavor also changes with refining and firing methods, we study it with the artist and produce it under optimum conditions.
Nosaka clay mining site near the Aikawa Gold Mine
This photo shows red clay: even within red clay there are red and yellow sections, each with different performance.
The following video shows the mineral-rich soils of Sado Island.
3. Many Red Teapots Made in Japan Are Colored with Artificially Added Iron Oxide Powder
Besides Sado, there are many teapots sold under the name Zhuni.
However, many commercially available red teapots are colored red by adding pulverized iron oxide (bengara, red iron oxide pigment) to ordinary clay and firing it in an oxidizing flame. I hear that natural Zhuni was once mined and fired in Tokoname, Shigaraki, Iga, Bizen, and elsewhere in Japan, but today, to my knowledge, natural Zhuni is still mined and used to make teapots only on Sado Island and in a very few other places.
Teapots made with added bengara do not improve the flavor of tea, regardless of their color.
This is because, in pottery containing bengara, the bengara melts during firing and covers the surface, causing the loss of porosity.
The melting point of bengara is low, at 600-800°C. When fired above 1100°C, it melts completely.
In contrast, in natural red clay, iron exists in crystalline form. Because crystalline iron has an extremely high melting point compared with bengara, it does not melt even when fired at the same temperature.
For this reason, pottery made from natural clay is thought to have a large surface area (porosity) and to release more mineral ions.
Incidentally, when teaware is made from the same natural clay, the lower the firing temperature, the more it changes the taste of water.
Firing at a high temperature means that more minerals reach their melting points. The pottery becomes stronger, but loses porosity.
Bengara is also used quite commonly on Sado.
Even if you visit Sado as a tourist and buy a teapot, it is not necessarily made from Sado clay. Even when Sado clay is used, it is common for it to contain a great deal of bengara.
The following video summarizes how natural clay is refined.
4. Benefits Found in Natural Red Clay
Teapots made from Sado's natural red clay make tea taste exceptionally good. In fact, you can perceive this simply by passing hot water through the teaware.
Hot water and tea that have passed through natural red clay gain depth of flavor, with a strong lingering finish at the back of the throat. This is also especially noticeable when brewing tea: tea brewed in glass or similar vessels has flavor that rises smoothly through the nose, whereas tea passed through natural red clay has flavor that seems to be drawn into the back of the throat, making its flavor quality and concentration feel richer.
These functions of red clay can naturally be experienced not only with tea, but with every liquid food, including sake, wine, coffee, fruit juice, and miso soup. When you eat soba or udon from a bowl made of natural red clay, the flavor suddenly becomes fuller and satisfaction increases. Incidentally, these functions are not observed with artificial Zhuni containing bengara.
The following two interrelated reasons explain why natural red clay has these functions.
1. The iron oxide contained in the clay is highly pure.
2. Iron oxide particles remain unmelted after firing, resulting in very high porosity and the release of more iron ions.
It is true that artificial Zhuni made by adding bengara also has a very high iron content. However, bengara melts like wax during firing, leaving an extremely small surface area. As a result, fewer ions dissolve out when hot water or tea comes into contact with the pottery.
Water is made of H2O molecules. Oxygen has a slight negative charge and hydrogen a slight positive charge, so neighboring water molecules attract each other like magnets and are connected by bonds called hydrogen bonds. These bonds are not fixed: water molecules move while changing direction, continuously breaking and reconnecting their bonds (Note 1).
When the temperature drops and molecular movement slows, hydrogen bonds align regularly and become fixed, forming ice. Ice floats on water because the molecules arrange themselves in a structure with many gaps. Conversely, when temperature rises, molecular movement becomes more vigorous, and molecules at the surface break free from hydrogen bonds and escape. This is evaporation. Water also has a high boiling point for such a small molecule because of these hydrogen bonds.
The structure of liquid water has not yet been fully elucidated, even by modern analytical chemistry (Note 2). However, when strongly charged ions dissolve in water, they attract surrounding water molecules and slow their movement (Note 3). It has been reported that this effect extends through the network of hydrogen bonds to several million water molecules per ion (Note 4).
I believe that mineral ions such as iron dissolved from natural red clay suppress the movement of water molecules, making aroma less likely to disperse and allowing the concentration of flavor and taste to be perceived at the back of the throat. This is only a hypothesis, but as explained at the beginning, the difference in lingering finish can be perceived simply by passing hot water through teaware.
When drinking tea, try holding it in your mouth without swallowing. What you perceive then is two-dimensional taste. But you do not feel satisfied unless you swallow.
Even with delicious ice cream, you cannot be satisfied just by holding it in your mouth.
The degree of satisfaction felt when swallowing is directly proportional to the quality of the ingredients.
The reason clam miso soup tastes better than ordinary miso soup is also related to iron ions released by the clams.
I believe this satisfaction is related to the strength of the hydrogen bonds inherent in the ingredients. The stronger the hydrogen bonding, the more strongly the lingering finish and the sense of satisfaction are felt.
Furthermore, porous pottery such as red clay has a large surface area and therefore a strong insulating effect, so the temperature drops less when tea is brewed and tea can be brewed at a hotter temperature.
5. Red Clay (Mumyoi) Is a Product of Volcanoes
Why does Sado have good clay?
In fact, Mumyoi clay has been mined and pottery made not only on Sado but also at gold and silver mines including the Iwami Silver Mine.
A common point is that red clay called Mumyoi is mined at all of these gold and silver mines.
Why does high-quality red clay come from gold mines?
By understanding how ore veins, including gold mines, were formed, we can understand the relationship between gold mines and red clay.
When lava erupts from underground, it pushes water upward at the same time.
Water deep underground becomes extremely hot under high pressure and dissolves metals lying beneath the ground.
The hot water pushed toward the surface together with the dissolved metals gradually cools over time, minerals crystallize, and ore veins are thought to form as a result.
When people hear Sado Island, they may think only of gold, but in fact many minerals besides gold are produced there, including silver, copper, titanium, and iron. Red clay is likewise part of a metal ore vein formed by the same mechanism.
Sado Island itself was formed by an undersea volcano. Considering this, it can be inferred that enormous quantities of minerals lie within the island.
Sado clay is little known in Japan, but it is in fact high-quality clay, rich in minerals of which the world can be proud.
When you think of Sado Island, the gold mine probably comes to mind first. The Sado Gold Mine, said to have supported the finances of the Edo shogunate, has a total tunnel length of 400 km. The mine was discovered in 1601 and closed in 1989. It is recorded to have produced a total of 78 tons of gold and 2,330 tons of silver.
The tunnel is closed for safety, but even near its entrance a variety of clays is exposed. The red rock is raw red clay.
6. Why It Is Called Mumyoi
In ancient China, red clay was used as a hemostatic agent. The herbal medicine scholar Li Shizhen completed the Compendium of Materia Medica (Bencao Gangmu) in 1578 (published in 1596), but in doing so noticed there was no appropriate name for “red clay.” Unable to think of a suitable name despite much consideration, he is said to have reluctantly used Mumyoi, meaning “a name that is not well known.”
During the Edo period, Japan imported “Mumyoi” from China as a hemostatic agent. However, it was discovered that red clay produced from Sado's gold mines had a similar hemostatic effect. Because it also looked very similar, it came to be called Mumyoi as well.
7. How Does It Compare with Yixing Zisha Teapots?
I am sometimes asked, “Which is better when compared with Yixing clay from China?”
There are many kinds of Yixing clay, but Yixing clays are collectively called Zisha.
Representative Zisha clays include Zhuni, Hongni, Benshan Lüni (Duanni), Lüni, and Zini, but not all of these clays have functions suited to brewing tea.
Yixing teapots are made with very high craftsmanship and are beautiful to look at, but not all of them improve the flavor of tea. If you actually pass tea or water through them and check how the flavor changes, you will find that a great many clays make the tea more astringent, more bitter, or flat in flavor.
Zhuni and Hongni, however, include clays with extremely high performance. I personally own, as part of my collection, a natural Yixing Zhuni teapot made before the Cultural Revolution, and its performance is beyond words. Such teapots are extremely rare and cost hundreds of thousands to several million yen, so they are not very practical. One reason old teapots perform well is that the clay is good, but it is also possible that firing with wood or charcoal, as was done at the time, affects the flavor. In fact, changing the firing method can change the flavor dramatically.
Tea ware made from Sado red clay performs exceptionally well, on a par with vintage Yixing Zhuni teapots.
8. An Extremely Labor-Intensive Traditional Technique: Namamigaki
Sado Mumyoi uses a technique not found in teapots from other production areas.
It is the technique called namamigaki (raw burnishing).
To perform namamigaki, the artist holds a shaped, unfired teapot and presses its surface with a smooth spatula, stone, or similar tool, compacting the clay surface to make it finer.
In particular, much effort is devoted to the base of the spout and handle. When namamigaki is done carefully, these areas have a natural finish, as though branches were growing from a tree trunk.
The body too develops a smooth, silk-like surface because its surface is thoroughly compacted.
This technique is actually commonplace in Yixing. The surfaces of Yixing teapots are very smooth for the same reason: they too receive namamigaki.
After namamigaki, the teapot is put in a box and dried further. As the clay shrinks during drying and becomes slightly distorted, namamigaki is performed again.
This work is repeated, and some teapots require as many as four days.
Other production areas also make glossy teapots, but these are made by buffing after firing or by simplified namamigaki, such as pressing the surface while it rotates on a wheel.
Compared with Sado teapots burnished by hand, the difference in finish is obvious even to an amateur at a glance.
Namamigaki Demonstration by the Wife of Tozo Watanabe of Kokuzo Kiln
When Tozo Watanabe's wife married into Sado, she says the first thing she learned from the previous generation was the technique of namamigaki. Her fingers embody 50 years of experience and skill.
9. The Current State of Mumyoi and Future Challenges
About ten artists work on Sado, but only two or three now specialize in making teapots. Furthermore, many artists use artificial Zhuni made with bengara. While these are certainly red in appearance and look like Mumyoi to the untrained eye, teapots with no functional qualities are increasing.
A major reason is the weakening of Japanese commitment to quality and their sense of values. The original function of Zhuni has been forgotten. Most people who buy Zhuni do not do so in search of delicious tea, but buy a Mumyoi teapot out of image or obligation, thinking, “I came to visit Sado, so I might as well buy Mumyoi as a souvenir.”
To preserve Sado's excellent teaware for future generations, it is important for young artists to develop and for the methods of making superior teaware to be passed down.
High-quality red clay still lies beneath the Sado mountain range.
Sado Mumyoi Series
To distinguish them from general “Sado Mumyoi,” HOJO names its Sado Mumyoi products by combining the clay type, firing method, and the name of the ceramic artist. The following are all works by Tozo Watanabe of Kokuzo Kiln.
- Nosaka Rough Clay, Oxidation Firing
- Nosaka Rough Clay, Reduction Firing
- Nosaka Rough Clay, Carbonized Reduction
- Akitsu Mumyoi, Oxidation Firing
- Akitsu Mumyoi, Reduction Firing
- Akitsu Mumyoi, Carbonized Reduction
- Mumyoi Joaka
Field Records
November 2013: Visiting Tozo Watanabe on Sado Island
References
Note 1 D. Laage, J. T. Hynes, "A Molecular Jump Mechanism of Water Reorientation", Science 311, 832 (2006)
Note 2 A. Nilsson, L. G. M. Pettersson, "The structural origin of anomalous properties of liquid water", Nature Communications 6, 8998 (2015)
Note 3 K. J. Tielrooij et al., "Cooperativity in Ion Hydration", Science 328, 1006 (2010)
Note 4 Y. Chen et al., "Electrolytes induce long-range orientational order and free energy changes in the H-bond network of bulk water", Science Advances 2, e1501891 (2016)
Shop Nosaka Rough Clay by Tozo Watanabe from HOJO (123) >
