"I want to leave the soil for future generations" [Listening to the voice of the soil: Column on Seto Hongyo Gama]

May 30, 2025

Seto City in Aichi Prefecture is a pottery production center with a history of over 1,000 years.
The reason for this is that the best clay for pottery, called "Gairome," can be extracted here.

Why is frog eye suitable for pottery?
Its main feature is its plasticity, which allows it to retain its shape like a shape-memory alloy, making it very easy to throw on a potter's wheel. It turns pure white when fired and is highly fire-resistant. If it is refined and the clay content is mixed with feldspar and silica, it can even be used to make porcelain clay.

It is truly a clay that was born for pottery. Thanks to this clay, pottery has been produced in Seto for over a thousand years. However, frogeye is a natural resource that is dug from the mountains, and as it is dug up, it disappears.

I would like more people to know about this.
We spoke to people involved in the ceramic raw materials industry and potteries who work with clay in Seto.

*If you would like to know more about frog eyes, please click here .

Seto Hongyo Kiln: A place that continues to convey the art of handcrafted craftsmanship

This time, we will be introducing Seto Hongyo Kiln, a pottery manufacturer that has been in business for about 250 years in the Hora district of Seto City, Aichi Prefecture. The workshop is located at the end of the "Kamagaki Path," which retains the traditional scenery of a pottery production area. In Seto, the main business refers to pottery. They cherish the idea of folk art and create their products by hand.

The clay they use is handmade using soil collected from Seto. It's an incredibly simple process. And because soil is a natural resource, the more we dig, the less it becomes. However, Yusuke Mizuno, the eighth-generation successor, says, "I don't want to use it all up in my generation, I want to preserve it."

Seto Hongyo Kiln is located in the Hora area of Seto City, about 1.5km from Owari Seto Station. In the mid-Edo period, they produced daily necessities such as plates and stone plates with a pattern known as Umanome, and in the Meiji period, they produced Hongyo Tiles, the first ceramic tiles made in Japan.

Here, they continue to do work that is similar to Seto's craftsmanship, a tradition that dates back to the Edo period or even before that.

"Hon'yo" refers to pottery. Since pottery has been made in Seto since ancient times, the newly introduced porcelain is called "shinsei."

Hora is a town in a valley between two mountains, and in the past there were countless climbing kilns that used to make use of the mountain slopes. At that time, "kamagaki" (walls) were created, carrying the kiln tools used in the climbing kilns. Over time, the people of the town have been working to preserve them.

This kiln wall stretches for about 400 meters, and the main street where artisans once came and went is named "Kiln Wall Path," retaining the atmosphere of a pottery production area.

In 2022, the Seto Folk Crafts Museum, a museum of craftsmanship and lifestyles, will open. Inside the museum, a climbing kiln, designated as a cultural property by Seto City, will be carefully preserved, and you can still feel the remnants of its original 13 chambers.

The purpose of the museum is to let people know about the local craftsmanship culture that has been passed down from our ancestors. It also aims to convey how pottery connects people and the lifestyles of the people behind it.

Handmade craftsmanship

At Seto Hongyo Kiln, we handcraft about 2,000 pieces per month, primarily using a potter's wheel for shaping.

The painting is done by painters using pigments made from natural materials.
By dividing up the work, each person repeats the same process over and over again. This allows the workers to become accustomed to the process, which improves both quality and production speed, which is why they produce in this way.

This is Kiseto pottery, the first glazed piece to be made in Japan. The glaze is made from the ash of red pine.

Horse eyes are also popular as antiques.

The straw hand is drawn with the image of an ear of wheat.

Making clay from raw soil

Now, let's start with the soil preparation. When I asked Yusuke about the soil preparation, he revealed all his secrets.

" We simply pulverize the raw clay (called white clay in Seto, containing frog's eye) collected from the mountains of Seto, sift it through a sieve , mix it with water, and let it sit. There are different grades of frog's eye, but we purposely choose coarse-grained clay with a rough taste to avoid making it too clean."

White clay.

"When you try to extract the clay from the raw clay, impurities are gradually removed in the process. As a result, the clay flavor ends up being closer to the clay in the porcelain. We simply mix the dried clay with water to return it to its original state in the mountain. This method is not common. It's a bit special."

Other things to add are wood-bush clay and It's chamotte.

This is Kibushi clay. Kibushi clay is made by adding water to dry clay to make it clay. This is added to make it easier to shape on the potter's wheel.

It has a strong ability to keep its shape and is often used by sculptors who make prototypes of dolls and other objects, but because it shrinks very easily, only a small amount is used.

Chamotte is crushed baked clay . It feels rougher to the touch than white clay. Kibushi clay shrinks a lot, so it is added to prevent it from shrinking too much. Once baked, it is less likely to shrink because it has already shrunk.

This is the mixture. The amount of water to add is determined by the hardness of the clay. This is the clay that has been left to sit for about a month.

Clay matured for three months. The whole piece has become more mellow.

The soil is made about once every two months. When it is used, it is passed through a kneader to mix it.

Changing soil

He says that as he touches the soil every day, the quality of the soil itself changes.

"When I asked my father, he said that clay these days is heavy. It feels more sandy than it used to. I think there's more silica sand being used in glass. I wonder if the amount of clay has decreased compared to the past."

Frog eyes contain a mixture of quartz, an impurity called kira, and clay. The high-quality part that many people desire is the " clay" part. The amount of this part is decreasing, and many people involved believe that the quality has deteriorated compared to the past.

However, Yusuke sees it differently.
"There are good things about that. Pottery is glazed on top of this, right? When it's fired in a truly good condition, the clay and the glaze on the surface fuse together and are truly fired. We call this 'eating each other'."

The image of them eating each other is when the glaze on the surface melts during firing, but the clay inside is not yet hardened. When this happens, the clay and glaze may not stick well together, but the silica sand helps them blend together.

Because they are dealing with nature, unexpected failures sometimes occur, but even in such circumstances, they make the most of the changes to create.

Towards a sustainable future for pottery

When we asked him about the ratio of ingredients used in making the clay, it was almost exactly the same as "Frog Eye." If this clay were to disappear, it would be impossible to bake the same thing. We asked him about his feelings towards the clay.

"We don't want to use it all up in our generation alone, but want to leave it for future generations. I think that's really what's at the root of it all. If we just think about the current mine, we're probably at a stage where we can work backwards, in fact. So, when it comes to what we need to do with current production, I think the answer is probably obvious already. But it's difficult to reduce production on one's own volition.

It's the same for everyone. It's something that moves with sales. It's hard for us to say, "Let's save money."

In this situation, Yusuke thinks that the first thing he can do is to make people aware of the actual situation.

"You make pottery, you sell it, and if it doesn't sell, it's stored in a warehouse. I don't think there's much guilt about that these days, either for the producers or the consumers.

If people knew that soil is precious, I don't think that would be a good thing. But right now, I feel like not everyone is even aware of that yet. Rather than blaming someone, I hope that by raising awareness, the situation will become a little clearer."

Little by little, moving forward.

[Listening to the Voice of the Soil: Introduction to the Series]