Kogatana: The Small Blade Beyond Its Role as Sword Fitting

What is the "Ko-katana"?—Accessory or Independent Blade

The term "ko-katana" (小刀) often causes confusion in the world of Japanese swords. Generally, the "ko-katana" is described as an accessory small blade housed in the hilt of a kozuka (小柄), but as a formal classification in sword studies, the "ko-katana" encompasses a far broader concept.

When small blades roughly 3–20 centimeters in blade length are collectively called ko-katana, they range extremely widely, from kitchen knives and chopstick shavers to craft knives and ko-katana attached to military implements. In the context of sword appraisal and sword culture, it is essential to distinguish between the ko-katana of sword furniture (the kozuka-fitted kind) and ko-katana manufactured as independent blades.

Classification by Form—Tsukurikomi and Blade Edge

The tsukurikomi (造り込み) of ko-katana is diverse, with the basic forms of Japanese swords condensed in miniature.

Kataha (片刃) ko-katana are the most common, existing in both shinogi-zukuri (鎬造り) and hira-zukuri (平造り) forms. Shinogi-zukuri, like the tachi and wakizashi, has a cross-section close to pentagonal, with the blade edge and mune (棟) clearly distinguished. Hira-zukuri has a blade body nearly flat in profile, with only the blade tip polished thin.

Moroha (諸刃) ko-katana are a form with both sides sharpened keenly, and are often manufactured for ritual and religious uses.

Kiriba-zukuri (切刃造り) ko-katana are used primarily in applications similar to tanto and wakizashi, with the angle of the cutting edge directly affecting blade strength and cutting performance.

The curvature (sori) of ko-katana is generally either straight or only slightly curved, though from the Muromachi period onward, forward-curved examples are also encountered.

Manufacture and Forging Technique

The manufacture of ko-katana is fundamentally based on the same forging techniques as tanto and wakizashi, but because the blade length is shorter, temperature management of the steel and the timing of hardening become more delicate. The thinner and finer the blade body, the more easily distortion appears during the hardening process, and the skill of the swordsmith is truly tested.

From the Kamakura period, examples survive of master smiths manufacturing complete sets of ko-katana as attachments to tachi and odachi, and it was considered an honor to provide ko-katana with the same jigane (地鉄) and hamon (刃文) as the main blade. Among the ko-katana manufactured by smiths of the Awata-guchi (粟田口) and Ki (来) schools, some receive high appraisal even as independent pieces.

Ko-katana as Sword Fitting Accessory—Its Relationship to the Kozuka

From the medieval period onward, a style was established of carrying ko-katana by inserting them into the sword fitting called kozuka (小柄). The kozuka refers to the hilt, and the blade part inserted into it becomes the "ko-katana." This integrated tool is sometimes called a "kozuka-fitted ko-katana" (小柄付き小刀).

The kogai (笄) and ko-katana were everyday items carried by samurai, used for eating, writing, personal grooming (particularly the kogai), and fine work in emergencies. When a swordsmith created an attached set with the same signature and jigane as the main blade, such a matched ensemble is valued highly in appraisal. The hamon of ko-katana attached to kozuka and kogai ideally possesses unity with that of the main blade, serving to maintain the aesthetic coherence of the entire sword fitting.

Between Utility and Art

During the Edo period, the ko-katana expanded from an everyday samurai tool to a practical instrument for intellectuals and craftspeople. Various craftspeople distinguished among specialized ko-katana for paper cutting, bamboo work, woodblock carving, and more. Even now, in Seki City, Gifu Prefecture and Sakai City, Osaka Prefecture—known as "blade-making regions"—specialized manufacture of ko-katana continues from the modern period to the present day.

From the perspective of collectors and enthusiasts, among attached ko-katana there exist pieces with high artistic and technical evaluation even as independent works. In particular, ko-katana attributed to medieval master smiths are evaluated by the same appraisal standards as the main blade.

Points for Appreciation

The points to observe when appreciating ko-katana do not differ essentially from those of appreciating the main blade.

• Jigane (地鉄): The appearance of hada (肌目) patterns (itame, masame, and mokume) and the refinement of the forging
• Hamon (刃文): The quality of concise blade patterns common in ko-katana, such as suguha (straight), ko-midare (small random), and ko-gunome (small interlocking)
• Nakago (茎): The presence or absence of a signature, file marks, and the form of the tang butt (such as kuri-jiri, sword-shaped, and others)
• Chikei (地景) and nie (沸): Fine observation of the surface features appearing in the jigane

By comparing them as an attached set to the main blade, the depth of the swordsmith's skill in "small works" becomes more clearly evident.

Basic Care and Storage

Ko-katana, like the main blade, are iron blades, and rust will develop if care is neglected. After appreciation, the standard procedure is to wipe away hand oils remaining on the blade body carefully with soft paper or cloth, apply a thin coat of oil, and then put it away. Even when stored with the blade inserted in the kozuka, it is best not to leave it inserted for extended periods, but to occasionally withdraw it and check the condition of the blade.

Storing them in a place free from excess moisture and in an environment without drastic temperature fluctuations is no different from caring for the main blade. If one simplifies handling because it is a small blade, rust often advances unnoticed until discovered. Because the blade body is small, once rust develops, its impact on the observable points of interest is relatively substantial, and this should be kept in mind.

Checklist When Acquiring

When considering acquiring a ko-katana or kozuka-fitted ko-katana, the following points should be confirmed:

• Blade condition: Presence or absence of rust and chipping, degree of wear from polishing. A small blade body has limited capacity for re-polishing.
• Signature and appraisal: Whether it is signed or unsigned. If there is a signature or expert attribution, confirm the explanation of the basis for the evaluation.
• Matching with the kozuka: Whether the kozuka and ko-katana are an original pairing or a later association.
• Photographs and recorded information: When purchasing online, confirm detailed photographs of the blade, nakago, and kozuka respectively, and verify the recorded dimensions.

Note that the legal classification of small blades differs depending on size and form, so it is prudent to confirm any unclear points with the seller before purchase.

At TOUKENZA, sword fittings including attached ko-katana are also available for viewing online. When considering a purchase, please be sure to confirm detailed photographs and provenance information.