Dobuchi Yoshiaki: Decoding the Secrets of Yohen Tenmoku

Yohen tenmoku is one of the most enigmatic masterpieces of tea ceramics. With its cosmic patterns and shimmering iridescence, it has captivated tea masters, collectors, and ceramic artists for centuries. Originating during the Southern Song dynasty (1127–1279 CE) in China, its extraordinary pottery glaze has remained a mystery—its precise crafting method lost to history, with successful reproduction long thought impossible. Only three known yohen tenmoku bowls survive today, all housed in Japan and designated as National Treasures.

Yet, Kyoto-based ceramic artist Dobuchi Yoshiaki, the fourth-generation head of Touan, has devoted himself to unlocking the secrets of this elusive art. Through thousands of relentless experiments with glazes, firing techniques, and kiln atmospheres, he has achieved what many believed unattainable. In this interview, he reflects on his artistic journey, the challenges of reviving a forgotten masterpiece, and the future of tenmoku ceramics.

When tenmoku was first introduced to Japan, the term simply referred to black-glazed tea bowls. Today, it's used more broadly to describe glazes rich in iron that produce deep, dark finishes. One of the most renowned centers of tenmoku production was the Jian Kiln in China, where many celebrated pieces—including the famous yohen tenmoku—were created. However, after the fall of the Southern Song dynasty, much of the region’s ceramic production was destroyed by the new ruling power, and the techniques behind tenmoku were eventually lost.

While all tenmoku pieces share a deep, reflective black surface, their characteristics vary dramatically. Some, like nogime tenmoku, display fine lines resembling the delicate streaks of rice grain husks, while yuteki tenmoku is defined by its scattered, metallic droplets. Each emerges through a distinct firing process, shaped by the careful manipulation of glaze composition, heat, and atmosphere.

Among them, yohen tenmoku stands apart—its surface scattered with luminescent patterns, each fleck cloaked in lapis-blue iridescence. The effect is ethereal, as if stars had been captured within the ceramic, their halos shifting between hues depending on the angle of light.

Most traditional Japanese ceramic techniques have been meticulously analyzed and reconstructed since the Meiji era (1868–1912 CE), but yohen tenmoku remains the sole exception. Despite centuries of study, the precise conditions needed to recreate its iridescent effect continue to elude complete explanation.

"Among all types of ceramics, yohen tenmoku remains one of the greatest enigmas. Many traditional techniques have been rediscovered and thoroughly studied, yet yohen continues to defy complete understanding," says Dobuchi.

It’s this enduring mystery that set him on the path to uncover its secrets. He began by studying historical records on togosan (tuhaozhan in Chinese), a glaze known as "hare’s fur" in English and nogime tenmoku in Japanese. Developed at Jian Kiln, this distinctive glaze became the foundation for his experiments. Yet even with these references, perfect replication was impossible. The natural evolution of raw materials, such as feldspar—essential in glaze formulation—meant their composition changed over time, requiring constant adjustments.

To achieve the mesmerizing effect of yohen, he tested thousands of glaze combinations, refined kiln atmospheres, and reconstructed firing techniques. In less than two years, he conducted between three to four thousand test firings—an extraordinary number in the world of ceramics. With each attempt, he analyzed the minute differences in color, texture, and structure, searching for a balance that would yield the shimmering depth characteristic of true yohen tenmoku.

"The process, at its core, is like a scientific experiment—forming hypotheses, testing variables, and refining each outcome. This applies not only to yohen tenmoku but to all pieces. Often, what seems like a mistake—a miscalculated formula or an unexpected firing effect—can lead to the most remarkable discoveries."

Unlike other tenmoku glazes, yohen tenmoku’s prismatic glow is an optical phenomenon. It is a result of an interaction of light refraction. This coloration, much like the wings of a jewel beetle or the sheen of an opal, allows the colors to shift depending on the angle of light.

"The brilliance of yohen tenmoku lies in the color shift—sometimes appearing deep blue, other times glowing in shades of purple and yellow. No other tenmoku has this kind of visual effect."

The crafting of tenmoku generally follows two distinct approaches. Some are formed through multiple firings, where a piece undergoes repeated exposure to different kiln conditions, allowing layers of color and texture to develop over time. Others rely on layered glazing, where one coat is applied over another, interacting within the heat of a single firing to create unique effects.

Yohen tenmoku achieves its celestial luster through multiple firings, with each phase altering the microstructure of the glaze. Through meticulous control of temperature and oxygen levels, Dobuchi orchestrates the emergence of yohen’s luminous blues, purples, and yellows.

"For yohen tenmoku, the most important element is not the size or shape of its patterns, but how vividly the colors emerge and transform with the light. That is the essence of its magic. Its beauty is most striking under natural sunlight."

While yohen tenmoku is considered the most elusive, other tenmoku finishes have long been celebrated for their beauty. Yuteki tenmoku, likened to oil-spot patterns, with its delicate silver or gold speckles, achieves its luster through controlled cooling. Konoha tenmoku, tree-leaf tenmoku, takes a different approach, incorporating actual leaves into the firing process, preserving their intricate organic patterns within the ceramic surface.

For Dobuchi, each glaze demands a deep understanding of both material and process. His approach to konoha tenmoku, for instance, extends from selecting the right species of tree to precisely timing the collection of each leaf. “The condition of the leaf determines eighty percent of the final outcome,” he explains. His relentless experimentation ensures that every piece carries both natural spontaneity and technical mastery, a balance he considers fundamental to his craft.

Beyond these classical styles, Dobuchi has also developed new variations. Koju tenmoku and Hekigyoku tenmoku are among his original works, the result of continued experimentation and the pursuit of newfound beauty.

Despite his success in reviving yohen tenmoku, Dobuchi acknowledges a fundamental truth—it is impossible to perfectly recreate the yohen tenmoku of the past. The conditions that gave birth to the surviving pieces, from raw materials to kiln environments, were unique to their time. Even with the most advanced knowledge and experimentation, exact replication remains out of reach.

But for Dobuchi, the goal is not replication—it is creation.

"The conditions of the past can never be replicated—the time, the materials, and the historical backdrop were all different. I know I can’t surpass what was made then. But at the same time, I believe I can create something just as beautiful in its own way."

Rather than chasing an elusive past, his work expands the very possibilities of tenmoku in the present. Whether through the cosmic glow of yohen or through his own original creations, his ceramics reflect both technical mastery and artistic vision, each piece capturing a beauty that transcends time.