Tanto Forging and How It Differs from Long Swords: Length Classes, Blade Forms, Forging Process and Features by Period

Tanto (short sword) refers to a Japanese sword with a blade length of less than 1 shaku (approximately 30.3 cm) (Nagoya Touken Museum "Tanto"). Although made with the same materials and processes as longer swords, their shape, construction, and usage have characteristics unique to tanto. This article organizes the similarities and differences between tanto and longer swords in order of definition, construction, forging process, and characteristics across different eras.

Definition of Tanto - Classification by Blade Length

Japanese swords are distinguished by blade length. Swords with a blade length of 2 shaku (approximately 60.6 cm) or more are called katana, those between 1 and 2 shaku are called wakizashi, and those under 1 shaku are called tanto (Nagoya Touken Museum "Why Do Japanese Swords Have Different Lengths?").

The following are examples of names for tanto and related classifications (Nagoya Touken Museum "Tanto").

• Aikuchi: Another name for a tanto without a tsuba between the blade and hilt
• Kaiken / Futokorogatana: Names for a tanto carried in one's sleeve or bosom
• Sunnobi tanto: Swords that have the form of tanto such as flat forging and little curvature, yet have a blade length exceeding 1 shaku. These appeared in the Northern and Southern Courts period and were actively made from the late Muromachi period through the early Edo period
• Yoroi-doshi: A collective term for sturdy tanto with a narrow blade width and extremely thick cross-section

Classifications based on usage and mountings are covered in detail in Types of Tanto.

Construction and Shape - Flat-forged with Little Curvature

Most tanto have flat forging without a ridgeline on the blade, with little or no curvature (Nagoya Touken Museum "Tanto"). This is the most obvious difference from longer swords with ridgeline forging and pronounced curvature. Besides flat forging, there are other construction methods common to tanto such as crown-drop forging, cormorant-neck forging, double-edge forging, and osoraku-zukuri. Types of construction are explained in 9 Types of Cross-sectional Blade Geometry and Complete Classification of Tanto Construction.

Even among the same type of tanto, there is great variation in cross-sectional thickness depending on the maker. The National Treasure "Tanto signed Yoshimitsu (renowned as Atsu Tōshirō)" held by the Tokyo National Museum is a 13th-century Kamakura period work measuring 27.6 cm in length with no curvature. It was called Atsu Tōshirō because the blade is extremely thick (e-Kokuho).

The Sword-Making Process is Shared with Longer Swords

Both tanto and longer swords are made through the following processes in the same order (Touken World "How Japanese Swords Are Made").

1. Mizuheshi: Tamahagane is heated and forged thin, then rapidly cooled in water (parts with high carbon content naturally fracture)
2. Kowari: Steel is broken into small pieces and sorted by hardness
3. Tsumiwakashi: Selected steel pieces are stacked, heated throughout, and combined into one
4. Fold forging: The steel is repeatedly forged and folded to remove impurities and equalize carbon content
5. Construction: Hard outer steel wraps soft core steel, creating a structure with a hard exterior and soft interior
6. Raw forging: The steel is forged to the desired blade length and shaped into the form of a Japanese sword
7. Clay coating and hardening: Clay is applied and heated, then cooled in water. The hamon and curvature form at this stage
8. Blacksmith pressing, tang finishing, and signature cutting: The blade is roughly polished, the tang is finished, and the maker's signature is engraved

The basic processes are the same as for longer swords. The difference in tanto is expressed in what form they take through these processes—that is, in their blade length, construction, and shape with little curvature. For detailed explanations of each process, please also refer to Tamahagane and Tatara Ironmaking and The Composite Structure of Kawagane and Shingane.

Differences Shown in Regulations - Forging Days

In the examination standards for authorization of artistic sword production published by Aomori Prefecture, the required number of forging days per sword is set as 15 days or more for tachi, katana, and naginata, and 10 days or more for wakizashi, tanto, and others (Aomori Prefecture "Examination Standards for Authorization of Artistic Sword Production"). This is an example of how the difference between tanto and longer swords is expressed numerically as an official standard.

To become a sword maker, one must train for at least 5 years under an authorized sword maker and complete the "Preservation and Training Program for Artistic Sword-making Techniques" sponsored by the Agency for Cultural Affairs (All Japan Sword Makers Association "For Those Wanting to Become a Sword Smith").

Tanto Through the Ages

• Kamakura to Muromachi periods: Used in grappling combat with enemies and in taking the heads of defeated enemies (Nagoya Touken Museum "Tanto")
• Master makers of the Kamakura period: Awataguchi Yoshimitsu of Kyoto and Shintōgo Kunimitsu, who established the foundation of the Soshu tradition, were both known as masters of tanto and are praised as twin pillars (Touken World "Yoshimitsu")
• Late Kamakura period to Northern and Southern Courts period: Rai Kunimitsu of Kyoto was known for his spirited tanto with strongly visible nie (Nagoya Touken Museum "Tanto")
• Northern and Southern Courts period: Sunnobi tanto with blade lengths exceeding 1 shaku appeared and were actively made from the late Muromachi period through the early Edo period
• Edo period: Their character as weapons for self-defense became more pronounced

Yoshimitsu's style and existing works are covered in The Life and Sword-Making Techniques of Awataguchi Yoshimitsu.

Summary

Tanto are made using the same tamahagane and through the same processes as longer swords. Differences appear in the blade length classification of under 1 shaku, the construction centered on flat forging and the shape with little curvature, and the forging days specified in the authorization examination standards. When viewing tanto, paying attention to blade length, construction, and cross-sectional thickness provides clues to understanding the era and purpose for which a particular tanto was made.