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

The "Exterior" of Koshirae Speaks to Sword Aesthetics

When discussing the appeal of Japanese swords, attention tends to focus on the blade's hamon and jihada, but the artistic quality of the "koshirae" (mounting) that envelops the blade is likewise one of the finest expressions of Japanese sword culture. Particularly in "daimyo koshirae" commissioned by daimyo and shoguns, the finest lacquerwork, metalwork, and textile techniques of the era were generously applied.

This article examines three representative lacquering techniques applied to koshirae: "shu nuri" (cinnabar lacquering), "aogai nuri" (mother-of-pearl inlay), and "iokakuji" (gold powder ground), explaining their artistic characteristics, historical backgrounds, and contemporary evaluation.

Shu Nuri (Cinnabar Lacquering)—The Dignity and Tradition of Red

Shu nuri is a technique that achieves vibrant red coloring by mixing ferric oxide (bengara) or cinnabar (mercury sulfide) into lacquer. It is one of the oldest color-application techniques in Japanese lacquerwork, and red lacquer has been confirmed on excavated lacquerware from the Jomon and Yayoi periods.

The use of shu nuri on sword mounts traces back to the "shu nuri no tachi" of the Heian period. Tachi swords presented as ceremonial weapons by samurai clans were finished with shu nuri covering the entire scabbard to visually demonstrate their "high rank."

During the Sengoku period, military commanders adopted shu nuri fittings for spears and naginata as a means of displaying their authority, serving both to ensure visibility on the battlefield and to demonstrate their power. Entering the Edo period, shu nuri scabbards were inherited as ceremonial swords for daimyo and were frequently used as commemorative gifts and presentation pieces by the various domains.

The technical characteristic of shu nuri lies in its combination with "roiro" (glossy finish) finishing. When layers of red lacquer are applied and finally polished with charcoal, then coated thinly with raw lacquer and burnished with deer antler—a technique called "roiro polishing"—a transparent depth is achieved. From simple red to refined deep crimson, the appearance changes dramatically depending on the craftsman's blending and technique.

Aogai Nuri (Mother-of-Pearl Inlay Lacquering)—The Brilliance of Luminous Shell and Raden

Aogai nuri is a type of raden (mother-of-pearl inlay) technique that exploits the "iridescent brilliance (structural color)" of the inner surface of shells such as luminous shells, abalone, and akoya pearl oysters. Thin pieces of shell are inlaid into the lacquered ground, and then coated with transparent lacquer and polished, producing a mystical brilliance that shifts color continuously depending on the angle of light.

By the Nara period, raden technique objects were already housed in the Shoso-in Treasury, and Japan developed this technique—which had been transmitted from the continent (Tang China)—into its own distinctive form. During the Heian period, "raden tachi" were treasured in court noble society as they were paired with formal court dress, and the technique spread to the warrior class during the Kamakura period.

The pinnacle of aogai nuri on sword mounts is represented by types such as "kin nashiji raden no saya" (gold pear-skin ground mother-of-pearl scabbard), which combines the technique of placing raden pieces on a makie ground sprinkled with gold powder called nashiji. The "kin nashiji aoi mon raden tachi koshirae" (gold pear-skin aoi crest mother-of-pearl tachi mounting) held in the Tokyo National Museum is known to belong to the Tokugawa family and is valued as one of the ultimate mountings demonstrating the shogunate's authority.

Contemporary aogai nuri craftsmen struggle with securing luminous shells. Once collected in Okinawa and Amami, luminous shells have been regulated due to resource depletion, and supply now depends on imports from Fiji, Vanuatu, and similar countries. The number of shells used in a single scabbard can range from dozens to hundreds, and production periods often stretch to several months.

Iokakuji (Gold Powder Ground)—The Golden Foundation Laid with Gold Dust

Iokakuji is one of the foundational processes in makie technique, referring to the "ground layer for flat makie" where gold and silver dust are densely scattered over lacquer to cover the entire surface. By literally creating "a ground laid with gold," it produces the effect of designs applied above appearing to float against a golden background.

It appears frequently on Muromachi-period koshirae and survives in forms such as "iokakuji matsu-gawa bishimon uchi-gatana koshirae" and "iokakuji shippo-mon itomaki tachi koshirae." During the Edo period, it was extensively employed on tachi mountings made as presentation pieces for shoguns and daimyo, creating dignified mountings where family crests such as paulownia, aoi, and chrysanthemum flowers glowed against the gold ground.

The texture of the ground varies depending on the particle size of the gold dust. There are variations such as "nashiji" using coarse gold powder (nashiji powder), "kinji" finished uniformly with fine gold powder, and "hyomon" with gold leaf applied. Craftsmen vary the type of powder and the sequence of layering applications according to the purpose and formal rank.

The drawback of iokakuji is that it is "susceptible to change." While gold dust does not oxidize, the lacquer used for adhesion loses transparency over time, and deteriorated mountings tend to become "faded gold ground." In museum conservation and restoration, maintaining a low-temperature, low-humidity environment to prevent lacquer degradation is essential.

The Comprehensive Art of Lacquerwork as Seen in Daimyo Koshirae

Edo-period daimyo koshirae were "comprehensive craft products" requiring division of labor and cooperation among multiple craftsmen to complete a single blade.

The woodworker (scabbard maker) shaped the magnolia wood into the form of a saya, while the lacquerer (nuryushi) applied dozens of layers of lacquer from the base coat to the final finish. The makie artist painted designs on the iokakuji ground and decorated with gold dust, silver dust, and colored lacquer, while the raden craftsman cut and inlaid shell pieces. The metalworker finished the tsuba, menuki, and koiguchi through chasing and repoussé work, while the grip wrapper completed the tsuka with ray skin and thread.

Because so many craftsmen were involved, it was not uncommon for a single daimyo koshirae to take several years to complete. The expense was enormous, and for pieces presented to the shogun, production costs in present-day terms were in the billions of yen.

Contemporary Craftsmen of Lacquered Koshirae

Even in modern times, only about 10 craftsmen nationwide are said to be capable of producing lacquered koshirae. Craftsmen who have mastered both lacquerwork and sword mounting are extremely rare, and their techniques face the serious problem of lacking successors.

While there are increasing cases of young craftspeople trained in lacquerwork at institutions such as Tokyo University of the Arts and Kanazawa College of Art developing interest in sword mounting lacquerwork, mastering techniques unique to sword mounting, such as "three-dimensional surface lacquering" and "interface treatment with tsuba and habaki," requires a minimum of 10 or more years of study.

The existence of craftsmen who apply the finest koshirae to contemporary masterwork blades using traditional techniques is of equal or greater importance to sword smiths in the transmission of Japanese sword culture. When sword collectors turn their attention to the lacquerwork of koshirae, it supports the preservation and transmission of these rare techniques.