Not many people have heard of a ceramic glaze called Tenmoku. Even fewer know the story of its “death” and “resurrection.” In this post, I provide a brief history of this amazing glaze that originated in China and spread to Japan, where it became a prestige glaze for tea bowls (chawans) used in the Japanese tea ceremony. I will also present three Tenmoku ceramic works by renowned Japanese artists to illustrate why Tenmoku is special.
Beginnings
Tenmoku originated in China’s Song dynasty (960-1279) as Jian ware, named after Fujian province where where abundant iron-rich clay and glaze minerals were available for their production. The name Tenmoku subsequently gained traction after Japanese Zen monks visited China’s Tianmu Mountain (Heaven’s Eye Mountain), saw the iron-glazed tea bowls used at local temples and brought them back to Japan. Once there, the beauty of Tenmoku tea bowls captivated tea masters who elevated them into symbols of high status and formal elegance in the Japanese tea ceremony.
With the fall of the Song dynasty, Tenmoku production ceased in China and the techniques of making Tenmoku ware melted into legend. Centuries passed without a single Tenmoku tea bowl made until the late 1970s when Chinese master craftsmen and researchers announced that rediscovered the lost art of making Tenmoku pottery. Parallel efforts to revive Tenmoku were undertaken by Japanese master potters such as Kato Takatoshi (1917–1999) who spent decades mastering the metallic speckle effects of what is commonly known as Yuteki or ‘oil spot’ Tenmoku.
Varieties of Tenmoku
Tenmoku glazes fall into three main types:
Hare’s Fur (Nogime): The glaze pattern is that of fine, vertical streaks formed by stretching iron crystals as the glaze melts as seen in the Chinese tea bowl above.
Oil Spot (Yuteki): The glaze pattern features shimmering silver or golden iridescent spots resembling oil floating on water, or stars glittering on a night sky.
Kiln-Change (Yohen). Rare and highly prized, the glaze pattern here is one of mesmerizing blue and purple iridescent halo spots that evoke images of the cosmos. Only three intact ancient Yohen Tenmoku tea bowls are known to exist in the world, alongside fragmentary pieces found in China. All three are in Japan where they are designated as National Treasures.
Why did it take so long to rediscover the secrets of making Tenmoku ware? The answer lies in the sheer difficulty of making them. To successfully produce a Tenmoku tea bowl for example, one needs high iron glazes which melt and run violently at peak heat, often sticking and fusing the piece to the kiln shelf, thus ruining the effort. In addition, the process requires precise temperature and oxygen reduction control. A tiny drop or spike in heat turns precious oil-spot crystals into an unwanted solid streak or ruins the pattern completely. The kiln also needs a precise reduction atmosphere (limited oxygen) to force iron from the glaze to separate and float onto the surface in the exact shapes desired, which is a tall order. Finally, heavy iron particles settle fast, making consistent glaze mixing hard. Up to 80% of firings fail because tiny shifts ruin the delicate crystal patterns like hare’s fur or oil spots.
While all three Tenmoku glaze effects are challenging to create, Yohen Tenmoku is universally recognized as the most difficult, requiring absolute precision in multi-stage reduction firing to produce the iconic shifting iridescent blue halos that define the style.
Tenmoku Gems
Featured here are examples of all three tenmoku effects, drawn from the Japanese ceramic collection of the Museum of Modern Ceramics SG in Singapore.
Hare’s Fur Tenmoku
This vase has a modernist abstract shape with a striking resemblance to sculptures by the Romanian avant-garde artist, Constantin Brancusi (1875-1957). The surface is covered with fine, hair-like streaks characteristic of ‘hare’s fur’ tenmoku ceramics. Kumakura Junkichi – the maker of this work – is himself an avant-garde ceramic artist, and according to a poll, one of most influential potters of the 20th century. He was a core member of the famed Sodeisha Movement founded in Kyoto in 1948 to champion ceramics as art.
Yuteki Tenmoku
This elegant sake cup is the work of Furutani Noriyuki, a rising star in Japanese ceramics. The cup captures the quiet beauty of Yuteki tenmoku with only a scattering of golden ‘oil spots’ on a lustrous black ground. The luminosity of the yellow oil spots gives this cup a clean, modern look that sets it apart from the majority of oil-spotted tenmoku tea ware.
Yohen Tenmoku
A tea bowl featuring a profusion of iridescent, ring-like spots resembling a starry night sky by Seto Takemi who is one of a handful of modern Japanese masters of Yohen Tenomoku. In 1990, while researching into Shino, Oribe and Ki-seto glazes, Seto was deeply moved when he saw a Tenmoku bowl in person. Later, inspired by a ceramic history book he found in Yokohama, he began experimenting with Tenmoku glazes and after much experimentation, he succeeded in creating the shimmering effects of Yohen Tenmoku. “I started tackling Yohen ware with no experience, and it took me 12 years. No one has figured out the secret to its firing; it’s like Fermat’s problem in mathematics, so (my success) was very rewarding,” he said, describing the enormous challenges he faced in mastering the technique. In October 2002, the culture section of the Nihon Kezai Shimbun featured an article that introduced his work along with a Yohen Tenmoku tea bowl designated as a National Treasure of Japan owned by the Seikado Bunko Art Museum.
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Museum of Modern Ceramics SG
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