The Smithing Craft of Japanese Spears: Forging Processes for Jumonji, Standard, and Katakama Yari Compared with Sword Techniques

Spear Smiths—The Relationship with Japanese Sword Smiths and the History of Labor Division

The spear (yari) is one of the representative types of Japanese bladed weapons and, like the Japanese sword (tachi and uchigata), is classified as an art blade weapon subject to regulation under the Firearms and Swords Control Law. Its manufacture is, in principle, carried out by swordsmiths (art blade weapon craftsmen) certified by the Agency for Cultural Affairs.

Historically, from the late Muromachi period through the Sengoku period, demand for spears increased explosively, and there are historical records suggesting that specialized "spear smiths" existed. However, in modern times, swordsmiths who specialize solely in spears are rare, and the general practice is to work in dual capacity—primarily making Japanese swords (uchigata and tanto) while also taking on spear work.

The first technical challenge that swordsmiths face when making spears is "selecting the form of the spearhead and designing the forging to suit that form." Spearhead forms fall into three main types—suyari, jumonji yari, and katakama yari—each requiring different forging approaches.

Manufacturing Process of Suyari—Precision Demands Within Simplicity

The suyari is a spear with a straight, simple spearhead form that appears the simplest in shape, yet demands high manufacturing precision.

The basic manufacturing process shares many commonalities with Japanese sword making. Materials are selected from tamahagane, and the base steel is homogenized through repeated folding. However, because the length of a spear's blade is shorter than that of an uchigata's blade, the total amount of steel used is less, but controlling the longitudinal form with precision requires unique technical expertise.

The cross-sectional form of a suyari spearhead is fundamentally shinogi-zukuri, with shinogi running along both sides of the blade to achieve both blade angle and strength. While similar to the shinogi-zukuri of a sword, the spear's primary use is for thrusting (tsuki), so piercing performance and resistance to breakage are prioritized over cutting sharpness. For this reason, the blade angle is set thicker than in swords, and the spine-side thickness tends to be designed thicker as well.

In the hardening process, like swords, clay is applied in graded layers (tsuchиoki) and the piece is heated in a furnace then quenched in water. However, because the spear blade is slender, controlling the angle and speed of insertion into the quenching tank is more difficult than with swords. When the difference in thickness between the thin spearhead and the thick base is large, localized temperature differences arise, increasing the risk of hardening cracks (yakiware). Experienced swordsmiths reduce this risk by varying the thickness of the clay application in a gradient from tip to base.

Forging the Jumonji Yari—Welding Techniques for Transverse Projections

The jumonji yari is a spear with bilateral symmetrical transverse projections (called a kama or horizontal blade) extending from the linear spearhead, a practical spear widely used by foot soldiers in Sengoku-period battles. Smiths from Settsu Province (present-day Osaka Prefecture) are known as representative producers.

The greatest technical challenge in making a jumonji yari is "joining the transverse projections." Modern manufacturing methods divide into two main types.

• Monolithic Forging Method: A method of cutting both the body and transverse projections as a unified piece from a block of steel. While possible using modern methods with gas or electric furnaces, when using only tamahagane from traditional tatara iron-making, acquiring a large unified steel block is difficult, so this method is rarely used in modern traditional techniques.
• Welding Forging Method (Kansetsu): The body (spearhead part) and transverse projections are forged separately and then joined by kansetsu—a blacksmith's welding technique in which pieces are hammered together at high temperature. This is the general method in traditional Japanese spear-making. Ensuring strength at the welded joint is the most critical task; if the base steel at the joint is unevenly mixed, there is risk of breakage in practical use. Pine resin and straw ash are used as flux in the kansetsu process, and careful temperature management at the joint is essential.

In designing the form of the transverse projections, the balance between the width and thickness of the projection's base is important. If the base is too thin, the projection easily breaks when lateral force is applied during thrusting. The blade angle of the projection also varies by maker, and the design changes depending on whether cutting performance or withdrawal performance after stabbing is prioritized.

Katakama Yari—Forging Difficulties from Asymmetrical Form

The katakama yari is an asymmetrically shaped spear with a sickle-shaped transverse blade on only one side of the spearhead. The katakama jumonji yari (katakama yari), which Kato Kiyomasa is known to have favored, is a famous example.

A unique difficulty in making a katakama yari is controlling "warping" (sori) during hardening caused by its asymmetrical form. In swords, controlling warping that occurs from heat treatment is one technique, with a designed amount of sori. In the katakama yari, however, having the transverse projection on only one side causes uneven shrinkage during heat treatment.

To control this, the thickness of the clay application is varied between the katakama side and the unadorned side to adjust heat absorption and release rates. Additionally, in the straightening (tame—form adjustment) process before hardening, a technique called "anticipatory correction" is required, in which the piece is intentionally bent in the opposite direction based on predicting the amount of deformation that will occur after hardening, then subjected to the hardening process. While this is the same in principle as warping control in swords, the calculation and practice become more complex for asymmetrically-shaped spears.

Design of Nakago and Shaft—Spear-Specific Long-Form Structure

The part of the spear blade that inserts into the shaft (e) is called the "nakago" or "stem" (nakago). Like the tang of a Japanese sword, it is where the maker's signature (mei) is inscribed, and it is a critical part that determines the attachment method to the shaft.

The tang of a Japanese sword is relatively short (around 20 cm) and is designed to fit completely within the hilt. The nakago of a spear, however, varies greatly depending on the shaft's material, length, and purpose. Battle spears are often designed with a longer nakago to increase contact surface area while considering the overall shaft strength.

In modern art spear production, shafts are made from wood such as magnolia (hoo) or oak (kashi). Unlike sword grips, spear shafts extend 1 to 3 meters in length, so the straightness of the wood and absence of knots directly affect shaft strength. It is uncommon for swordsmiths themselves to make shafts, and in some cases coordination with shaft makers becomes necessary.

Polishing and Finishing—Characteristics of Processes Different from Swords

The completed spearhead undergoes a final polishing process by a polisher (togishi), as with swords. However, because the spear blade form differs, the polishing process also differs from that of swords.

In the case of suyari, the process is similar to sword polishing. However, with jumonji yari and katakama yari, special placement of whetstones is needed to polish the curved surfaces of the transverse projections, and the interior curved surfaces of the projections must also be polished. Particularly with the interior of the transverse projections on jumonji yari, whetstones cannot easily reach, so specialized techniques such as using thin whetstones or tip-worked whetstones are required.

The hamon on spears is predominantly straight (suguha) or small wave pattern (komidaré) on suyari, with a tradition of emphasizing practical uniformity over aesthetic evaluation. However, in modern art spears, examples exist with highly aesthetic gunome and choji wave patterns.

Summary—What Spear-Forging Technique Demands of Swordsmiths

Spear production builds on Japanese sword forging techniques while requiring the acquisition of unique skills due to the spear's distinctive form, purpose, and structural characteristics. Whether swordsmiths can apply the heat treatment control, kansetsu technique, and polishing sensibility developed through Japanese sword-making to the spear's different forms, dimensions, and requirements is one measure of their technical skill.

The number of existing art spears is far fewer than Japanese swords, and naturally, opportunities to make them are limited. However, given the historical and martial significance the spear holds in Japanese blade culture, the transmission of spear-making techniques to the next generation of swordsmiths is a meaningful endeavor in preserving the full scope of Japanese blade-forging techniques.

Those interested in bladed weapons can view blades currently featured in TOUKENZA's online catalog.