Lacquer Arts on Japanese Sword Mountings: Vermilion, Aogai Shell, and Ikakeji Techniques in Daimyo Koshirae

The Aesthetic Philosophy of Japanese Swords Told Through Koshirae's "Exterior"

When discussing the allure of Japanese swords, the eye tends to focus on the hamon and jihada of the blade itself. However, the artistic standard of the koshirae that envelops the blade is also one of the pinnacles of Japanese sword culture. In particular, the "daimyo koshirae" commissioned by daimyo and shoguns incorporated the techniques of lacquerwork, metalwork, and textiles at the highest level of the time without reserve.

This article examines three representative lacquering techniques applied to koshirae—"shu-nuri," "aokainuri (mother-of-pearl)," and "ikakerji"—and explains their artistic characteristics, historical backgrounds, and contemporary evaluations.

Shu-nuri (Red Lacquer)—The Dignity and Tradition of Red

Shu-nuri is a technique that produces a vivid reddish color by mixing bengara (iron oxide) or cinnabar (mercury sulfide) into lacquer. It is one of the oldest color-application techniques in Japanese lacquerwork, with red lacquer confirmed on excavated lacquerware from the Jomon and Yayoi periods.

The use of shu-nuri in sword mountings traces back to the "shu-nuri no tachi" of the Heian period. Tachi presented as ritual swords of the warrior class or as rewards were finished entirely with shu-nuri scabbards to visually demonstrate "high status."

During the Sengoku period, warlords adopted shu-nuri fittings for spears and naginata as a "means of displaying imposing authority," combining visibility on the battlefield with the display of power. Entering the Edo period, the tradition of red lacquer scabbards was maintained for daimyo ceremonial swords and was highly valued as commemorative gifts and presentation pieces for each domain.

The technical refinement of shu-nuri lies in its combination with "ro-iro finishing." From plain red to elegant deep crimson, the appearance changes greatly depending on the craftsman's proportioning and skill, but the representative process is as follows:

1. Apply red lacquer in multiple coats
2. Abrade with charcoal and charcoal dust
3. Apply a thin coat of raw lacquer and polish with deer antler (ro-iro polishing)

This creates a deep, luminous transparency.

Aokainuri (Mother-of-Pearl Lacquer)—The Brilliance of Night-Shining Shell and Mother-of-Pearl

Aokainuri is a type of raden technique that utilizes the "iridescent brilliance (structural color)" found on the inner surfaces of night-shining shells, abalone, and akoya shells. Thin pieces of shell are inlaid into the lacquer base, and transparent lacquer is layered over them and abraded, creating a mysterious radiance that shifts in color depending on the angle of light.

As early as the Nara period, mother-of-pearl objects were stored in the Shosoin, suggesting that Japan had uniquely developed techniques transmitted from the continent (Tang). In the Heian period, "raden tachi" were treasured in court society in combination with formal court dress, and by the Kamakura period, they had spread to the warrior class as well.

The pinnacle of aokainuri in sword mountings is the "kin-nashiji-raden-no-saya" class. This combined technique places raden on a makie base scattered with gold dust called nashiji. The "Kin-nashiji Aoi-mon Raden Tachi Koshirae" in the Tokyo National Museum is known as a treasure of the Tokugawa family and is evaluated as one of the ultimate koshirae embodying the shogun family's status.

Contemporary aokainuri craftsmen struggle with securing night-shining shells. Night-shining shells once harvested in Okinawa and the Amami Islands are now regulated due to resource depletion, and current production must rely on imports from Fiji, Vanuatu, and elsewhere. The quantity of shell used on a single scabbard can range from dozens to hundreds of pieces, and production periods often extend over several months.

Ikakerji (Gold Powder Base)—The Golden Foundation Laid with Gold Dust

Ikakerji is a foundational makie technique that densely sprinkles gold and silver powder over lacquer to cover the entire surface, serving as "the base for flat makie." By literally creating "a ground laid with gold," the designs applied atop it appear to float against a golden background.

Frequently seen on mountings from the Muromachi period, it exists in the form of "Ikakerji Matsukawabishi-mon Uchigatana Koshirae" and "Ikakerji Shichipo-mon Itomaki Tachi Koshirae." During the Edo period, it was actively adopted for tachi koshirae made as presentation pieces to shoguns and daimyo, and family crests such as paulownia, hollyhock, and chrysanthemum were rendered against gold grounds, creating refined koshirae.

The texture of the base varies depending on the particle size of the gold dust. The variations are as follows:

• Nashiji: Uses coarse gold dust (nashiji powder)
• Kinji: Finished uniformly with fine gold dust
• Hyomumon: Gold leaf is applied

Craftsmen skillfully differentiated the type of powder and layering sequence according to the use and status.

The drawback of ikakerji is that it "changes easily." The gold powder itself does not oxidize, but the lacquer used for adhesion loses transparency over time, and faded koshirae readily become "discolored gold grounds." In museum conservation, maintaining a low-temperature, low-humidity environment to suppress lacquer deterioration is essential.

The Comprehensive Art of Lacquerwork Seen in Daimyo Koshirae

Edo-period daimyo koshirae were "comprehensive craft works" in which multiple craftsmen collaborated through division of labor to complete a single sword. The responsibilities were divided as follows:

Because so many craftsmen were involved, the completion of a single daimyo koshirae often required years. Costs were enormous, and for pieces presented to the shogun, it is believed that production expenses in modern value would reach hundreds of millions of yen.

Contemporary Craftspeople of Lacquered Koshirae

In contemporary times, craftspeople capable of producing lacquered koshirae number only about ten nationwide. Craftspeople who have mastered both lacquer art and sword mounting are extremely rare, and their techniques face the serious challenge of a lack of successors.

Young practitioners who have studied lacquer art at Tokyo University of the Arts and Kanazawa University of Art and Crafts have increasingly shown interest in sword-mounting lacquer art. However, acquiring the techniques specific to sword mountings—such as "three-dimensional lacquering of surfaces" and "the joining of tsuba and habaki"—requires at least ten or more years of apprenticeship.

The existence of craftspeople who apply the finest koshirae to contemporary masterpieces using traditional techniques holds importance in the transmission of Japanese sword culture that is comparable to that of sword smiths. When collectors turn their attention to the lacquer art of koshirae, they also contribute to the preservation and transmission of this rare technique.