What happens when you bake clay? [Listening to the Voice of the Clay: Column by Miyama Pottery Studio]

June 1, 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 you refine it to extract the clay and mix it with feldspar and silica, you can even make clay for porcelain.

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.

We would like more people to know about this and become more interested in it. We spoke to people involved in ceramic raw materials and potteries who handle clay in Seto.

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

The fourth installment is "Miyama Pottery Studio."
Since opening the kiln in the early Meiji period, the fourth-generation Terada Yasuo and the fifth-generation Terada Teppei have been active as potters, focusing on producing Oribe-style tableware for traditional Japanese cuisine.

Professor Yasuo was fascinated by the changes in clay during firing in a wood-fired kiln. During his half-century career as a potter, he has built over 50 kilns both in Japan and overseas, and has come face to face with the changes that occur in the clay inside the kilns.

Pottery is said to be the art of earth and fire. We spoke to him about "earth and firing" from a potter's perspective.

In search of the perfect clay and kiln

Professor Yasuo Terada and Teppei in front of their homemade wood-fired kiln made from stacked bricks.

Miyama Pottery Studio has a studio in the Akazu district of Seto City, which has long been a popular spot for people involved in pottery. Climbing a small hill, you will come across a large gate, and on the spacious grounds you will find the studio and a handmade wood-fired kiln.

"Pottery Kiln Basics and Kiln Building Records" (Satobun Publishing) was released in 2020 as a compilation of kiln building . It contains a variety of kiln building records and essays on the experiences, making it very interesting.

The fourth generation, Yasuo Sensei, is a ceramic artist who has built over 50 kilns both in Japan and overseas during his half-century career, and is like a walking encyclopedia of kiln construction.

"I started building wood-fired kilns just before I turned 50. When you fire in a wood-fired kiln, the appearance of the clay changes drastically. It's completely different from electric or gas kilns. That's when I became interested. Up until then, I hadn't been interested because I had to keep making things as a potter, but now I have a little more free time.

So we started making a variety of different kilns, and the changes in the soil were huge, so we dug up soil from all over the place and did a variety of tests."

He has been researching materials for about 10 years, digging up soil from all over Japan, including the Setouchi Inland Sea, and firing soil in various states, including crushed and sieved, washed and sieved, and elutriated.

"Looking back, I was able to make a good living (laughs)."

At that time, he also began to focus on publishing, and in 1998 he published "The Basics of Clay and Molding" (Futabasha), which thoroughly introduced everything from raw clay to molding. He says that he made many discoveries as he continued to pursue clay.

I'm sure you all have soil all around you, but I don't think many people have ever thought about what would happen if they burned it.

"Raw clay changes a lot. When it's freshly dug up from the mountains, it's full of scum. You can either bake it as is, or you can bake clay that has been refined once. You can bake it in an electric kiln, a gas kiln, or a wood-fired kiln. The appearance of the clay changes drastically when you use a wood-fired kiln.

Those that can be fired at high temperatures become the " clay" that is the raw material for pottery . However, there is some clay that melts. In fact, there is a lot of it. When it melts as the temperature rises, it becomes the glaze. The ones that don't melt become the body.

"Soil has limitless charm."

As you talk, it becomes clear that clay changes dramatically when it is fired. Having fired clay from all over the country, what is the appeal of Seto clay?

"The appeal of Seto clay is that it can be used for anything. You can use Seto clay to create Bizen or Hagi style pottery. You can really do anything with it. Because you can do anything with it, it seems like it doesn't have any particular characteristics."

Seto clay is easy to mold, so both Bizen and Ogi styles can be made with more freedom than the originals, without any restrictions on shape.

"For example, if you want to make something in the Bizen style, you can use Seto clay. Even when the temperature gets extremely high, the body remains intact . Clay from Bizen would melt or dent."

Even at over 75 years old, Professor Yasuo's enthusiasm for creating art remains undiminished.

"Soil has limitless charm."

Teppei Godai's approach to clay

Firing in the wood-fired kiln inside the workshop.

Meanwhile, Teppei, the fifth generation, took Yasuo as his master and built many kilns together with him, even going to look for raw clay.

Because of this experience, he feels that the act of creating pottery from raw clay is becoming more difficult as time goes on.

"The most enjoyable thing is playing with wild clay and creating works of art. However, it is quite difficult to find time to study clay while working as a potter and an artist.

Also, in my father's time, there were a lot of people who walked in the mountains. People who went to dig for yam or chase wild boars would tell me when they found a layer of clay that they were looking for.

But now those people are getting older, and there aren't many people in the world who venture into the mountains, so there's inevitably less information available."

Pursuing the old and new Oribe.

This is a vessel that shows the natural texture of the clay through carbonization firing, in which the work is fired without glaze , with charcoal placed inside .

When I read articles written by Professor Yasuo himself, I learned that in the past, it was common for people to venture into the mountains that had been passed down from generation to generation to gather raw materials. However, in this day and age, even if you look around, you don't see many people venturing into the mountains.

Teppei is aware of the changing times and continues to work with an eye to the future.

"I foresee a time when it will no longer be possible to create works using ceramics. Perhaps clay will become a different material. When I make a failed piece, I apologize to the clay in my heart. It means that I have used a valuable resource to produce industrial waste ."

As I spoke with them, I realized that pottery is something that people naturally devote their lives to pursuing. I also felt a strong sense of respect for the clay.

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