Sashimono: The Subtle Art of Japanese Wood Joinery

See how the "impossible joint" is made without glue or screws.
Eric James Beyer
Japan's art of wooden joinery.Dylan Iwakuni

Carpentry is a discipline that elegantly merges form and function. The Japanese woodworking tradition of sashimono—a word derived from monosashi, meaning “woodwork ruler”—is an embodiment of how beautiful that synthesis can be.

“We work with this material as an instrument, to fashion useful objects, possibly if so willed a thing of beauty. In any case, a joining of the rhythms of nature to fulfill its own destiny and ours.” 

What is sashimono woodwork?

Sashimono is the tradition of making furniture without the use of nails or screws of any kind. Instead, complex wooden joints carved out with simple chisels, handsaws, and planers are used to create pieces that are as sturdy as they are refined. 

Due to the creativity inspired by this reliance on a single building material, the joints in sashimono are often intricate works of art in themselves. Though they will go unseen once the build is assembled, the precise construction and arrangement of this joinery enables the finished pieces to last for hundreds of years. 

Importantly, the tradition places a high philosophical value on working in tandem with nature rather than against it. The reverence for wood as a material comes from the fact that, even as recently as 2010, 69 percent of Japan was covered in forests, according to official UN figures.

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Combine this with the fact that iron was not readily available at the time of sashimono’s origins, and it’s easy to see how carpenters in Japan developed building techniques that have made excellent use of the abundant natural resource.  

Japan’s deep bond with woodworking goes well beyond convenience, however. Before his death in 1990, George Nakashima, a renowned carpenter who worked with wooden joinery and author of The Soul of a Tree: A Woodworker’s Reflections, summed up this philosophy by saying, “We work with this material as an instrument, to fashion useful objects, possibly if so willed a thing of beauty. In any case, a joining of the rhythms of nature to fulfill its own destiny and ours.” 

Sashimono is inherently tied to this way of thinking. Its beauty is best appreciated not only through its technical specifications but also through Japan's history.

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Tokyo by way of Kyoto

Two styles make up the bulk of the sashimono tradition, Kyo sashimono (Kyoto style) and Edo sashimono (Tokyo style), both of which have been practiced in Japan for centuries. 

"The craft brings out the utmost beauty of the wood grain colors and texture.”

According to Kogei Japan, an organization that specializes in traditional crafts officially defined by the Japanese Ministry of Economy, Kyo-sashimono historically focused on producing display cabinets and boxes for ritual tea ceremony (chanoyu) utensils. Kyo furniture is marked by a regality and flair that was preferred by the Imperial Court members and societal elites who it was made for during the Muromachi period (1336-1573). 

This style, which often featured opulent ornamentation through the use of gold leaf and thin lacquering, evolved out of the wood joinery practices of the Heian period (794-1185), after which sashimono carpentry became increasingly nuanced. 

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Paulownia wood is often used in Kyo sashimono constructions due to its resistance to heat and moisture, but other commonly used timber includes Japanese cedar, cherry, Japanese zelkova, and pine. 

Edo sashimono comes, unsurprisingly, from Japan’s Edo period (1603-1868). This period is also known as the Tokugawa period, named after Tokugawa Ieyasu, the Shogun (military government) leader who was able to bring an end to the state of near-constant war between various houses and regional leaders known as daimyo. The stability that marked Ieyasu’s reign resulted in a greater demand for furniture and other household items as a consumer class began to emerge. In this way, sashimono spread beyond the Imperial Court and took on a new form.

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In comparison with Kyo sashimono, Edo furniture was used by samurai families, merchants, and actors of the famous kabuki theater tradition, a type of Japanese stage play that incorporates dancing, miming, and elaborate costuming. Despite being less flashy than Kyo furniture, Edo sashimono achieves an elegance of its own by calling attention to the beauty of the wood itself rather than relying on striking ornamental features. Edo sashimono artisans only work with wood sourced from within Japan, with mulberry wood from Mikurajima island being a particularly prized variety.

Yutaka Mogami is a master edo craftsman whose father founded the Edo Wood Joinery Association, a collection of sashimono carpenters carrying the tradition into the modern era. In an interview with Nohga Hotel in Tokyo, Mogami elaborates on how sashimono pulls together structural and visual elements to create something quietly sophisticated that is representative of its history:

“Edo sashimono pays great respect to the refinement of the Edo period. It uses thin panels and slender columns compared to other joinery forms, and while it may seem dainty and elegant at first glance, it is actually sturdily joined just out of view. This is the defining feature of Edo sashimono compared to other areas' sashimono craft, and [it is] the very essence of the aesthetics of refinement. The craft brings out the utmost beauty of the wood grain colors and texture.”

"Hinoki cuts clean, and is at its strongest two centuries after being cut down. That’s why Horyuji has stood for 1300 years.”

There is a third tradition of sashimono called Osaka karaki sashimono. This variant hails from cities within the Osaka prefecture. Like Edo and Kyo, it prioritizes attention to detail and and long-lasting construction methods, but differs in that it uses imported woods like ebony and rosewood. According to the Japanese Traditional Aoyama Square art gallery in Tokyo, Osaka karaki sashimono specializes in creating desks, tables, and tea shelves.  

Different joints of view 

Edo, Kyo, and Osaka karaki traditions vary slightly in how they realize a particular build, but they all follow similar processes. Artisans start by cutting the timber into blocks, with an eye to revealing the natural pattern of the grain. Once the blocks are smoothed down by planers, the joints are then carved into the piece and the whole thing is put together for a preliminary fit. Any necessary adjustments are then made and the piece is reassembled, oftentimes using a mallet to fit the parts together. Once that happens, it's nearly impossible to disassemble without either the right tools and knowledge or brute destructive force. 

Of course, the big draw of sashimono is the largely concealed joint work, hidden away within the furniture itself. The Art Research Center at Ritsumeikan University in Kyoto, Japan, in collaboration with Kyoto Women’s University, explains that sashimono joinery relies on two techniques. The first is hozo, the joining of extended or projecting pieces called tenons with perfectly-fitting recessed slots called mortices. The second is tsunagi, joinery based on delicate geometric patterns. 

There are dozens of joint types that master carpenters use in their work, ranging from the relatively simple to the dauntingly complex. A Twitter account called The Joinery is a great place to visualize this joint work, as it displays hundreds of 3D models that detail how these multifaceted sashimono joints come together. The digitizing of these traditions is a happy development. Because sashimono and other carpentry techniques in Japan are handed down largely in a hands-on manner via master-apprentice relationships, online resources regarding the specifics of these joints can be hard to find. 

Of the techniques used by sashimono artisans, one intimidating joint type is shiho kama tsugi, the four-faced gooseneck joint. It’s made by carving out two gooseneck hozo tenons that, when finished, slide diagonally into a mortise, locking together tightly. 

The Complete Japanese Joinery, a compendium of traditional joints and their schematics, explains how shiho kama tsugi is commonly found at the columns of shrines and temples throughout Japan. This hints at how Japanese joinery techniques have spread throughout the various forms of carpentry in the country, scaled up and down according to each tradition’s needs. 

Horyu-ji: the oldest wooden building in the world

One such related tradition is that of the renowned miyadaiku, carpenters who excel at construction using wooden joinery similar to that of sashimono, but scaled up to form the framework of temples and shrines. 

Located in the Nara prefecture, the Horyu-ji temple complex is a pristine example of the work of miyadaiku carpenters. According to UNESCO, 11 of the buildings in the complex date from the late 7th century, meaning they are among the oldest standing wooden structures in the world. 

Sashimono: The Subtle Art of Japanese Wood Joinery
The main pavilion and five-story pagoda at Horyu-ji temple sit under dynamic grey skies. Source: Angel de los Rios/Flickr

The complex is important for a number of reasons. The buildings there show how Japan incorporated the Chinese architectural principles that are the foundation of the country’s carpentry traditions. They also mark the introduction of Buddhism into Japan, which had a huge impact on the trajectory of architecture there in the following centuries.

Among the architectural principles found at Horyu-ji is a post-and-lintel construction based on the Chinese bay system, where columns hold up horizontal beams. In Horyu-ji’s case, we see a modified version of that system, a heavily bracketed design that transfers the weight of the ceiling down to the columns below. 

The temple columns are also examples of a principle called entasis, which is a slight convex curve is purposefully given to columns that corrects for the optical illusion of hollowness when tapered columns are seen from a distance. Like sashimono furniture, the miyadaiku carpenters at Horyu-ji constructed it using wooden joinery. It should be noted, however, that according to a paper published in the journal Association for Preservation Technology International, both the five-storied pagoda and main pavilion at the temple complex have since been reinforced with steel to prevent structural defects from causing damage to the site. 

Almost as incredible as the age of the temple complex at Horyu-ji is the lineage of artisans that can be traced back directly to the original builders of the temple. 

The only apprentice of the late Tsunekazu Nishioka, the descendant of a line of carpenters who oversaw work at Horyu-ji, is a man named Mitsuo Ogawa. In an interview with the Japanese government’s Public Relations Office in 2018, Ogawa remarked on how the carpenters at Horyu-ji had the foresight to choose their timber carefully:

“Horyuji Temple is made of hinoki cypress [...] If it were cedar, it would have lasted about nine hundred years. But hinoki cuts clean, and is at its strongest two centuries after being cut down. That’s why Horyuji has stood for 1300 years.”

Sashimono: The Subtle Art of Japanese Wood Joinery
 Source: Karen Eliot/Flickr

All wood things in time

Ogawa, like other Japanese carpenters, is worried about the future of these traditions. As deforestation begins to take its toll in the country and modern lifestyles drive down demand for elaborate carpentry, miyadaiku and sashimono traditions will need to find their place in a new generation of carpenters. 

Yutaka Mogami echoes these feelings.“The demand for wood joinery furniture has been disappearing with the changes in our living spaces and customs,” he says. “So the challenge we face going forward is to understand the modern way of life and create works that are easily accessible for the younger generation. To do that, we need a sense of balance between preserving our traditional techniques and creating something new.” 

Traditional Japanese carpentry student Dylan Iwakuni, a Kyoto native, is an inspiring example of someone who is folding these traditions into the future. After attending a carpentry trade school in Japan’s Gifu prefecture and helping to renovate old shrines as an apprentice under a woodworking master in Kyoto, Dylan now spends his time perfecting his Japanese joinery skills and holding workshops with the Florida School of Woodwork to help educate people in these traditions. 

He also runs a fantastic YouTube channel and manages an Instagram page where he posts photos and videos of the construction of various joints used in sashimono and miyadaiku carpentry, from the relatively straightforward ari shiguchi (dovetail) joint to the absurd shihou kama tsugi (four-way goose neck joint) mentioned above.

Encouragingly, people like Dylan Iwakuni are reanimating these storied traditions and carving out a space for them in the modern era. With any luck, the future of miyadaiku and sashimono artisans will be as diverse and resilient as the brilliant woodwork they produce.