Sword Masters' Oral Transmission and Secret Technical Documents: The History of Transmitting Written and Unwritten Techniques

Technology to "Write" or "Speak" — Two Paths of Transmission

The techniques of Japanese sword craftsmanship have been passed down from master to apprentice over many years, but the methods of transmission can be broadly divided into two. One is "kuden" — the direct oral transmission of knowledge — and the other is "hidensho" — technical documents written and preserved in writing.

The distinction between these two methods has deep philosophical roots. The choice of what to write and what not to write was not accidental, but rather a "knowledge management strategy" intentionally designed by each school and individual sword maker.

Hidensho — The World of Written Technique

Technical documents left by sword makers vary in nature. The most well-known are quenching-related documents such as "kirihagaki" and "yakiba hidensho." These describe the quenching process, which is the most critical step in determining the shape of the blade pattern, including "clay composition," "how to discern fire temperature," and "how to immerse in water."

The following are known among researchers as representative existing hidensho:

• "Honami Family Hidensho": A collection of multiple documents left by the Honami family, which holds the highest authority in Japanese sword appraisal, relating to appraisal techniques and the history of Japanese swords. It includes information on the practical work of appraisal, such as the shape of blade patterns, characteristics of jihada, and evaluation criteria for polishing. However, the "core secrets" are said to have been reserved for kuden and were not written in documents.
• "Shintou Kaji Hiden" Type Documents: A general term for technical books written during the Edo period's shintou era. Rather than belonging to any single school, these are collections of individual technical notes left by multiple sword makers and master craftsmen. They describe iron selection methods, procedures for clay application, and precautions for quenching.
• "Yamashiro and Bizen Forging Records": Technical notes on the manufacturing process recorded by sword maker groups from various production regions from the Muromachi through Edo periods. These have more the character of "school official documents" than individual hidensho, and served to transmit technical information necessary for the continuation of the school to succeeding generations.

Unwritten Techniques — What Kuden Preserves

What is important is the existence of techniques that were "not written" in hidensho.

In Japanese traditional craftsmanship, the philosophy that "the most important techniques are not put into writing" is widely shared. In the case of sword makers, the following techniques in particular were transmitted only from master to apprentice through kuden and were intentionally kept from being documented.

• Clay Composition Ratio: The specific component ratios of the clay used for quenching — the proportions of whetstone powder, charcoal powder, clay, and other additives — are the greatest secret of each school. While hidensho may state the fact that "clay is used to create blade patterns," they do not write "what is mixed in what proportions." This is based on the thinking that "even if one knows the recipe, it cannot be used without a sense of fire control, water temperature, and immersion method."
• Discerning Fire Temperature: The determination of whether the blade has reached the appropriate temperature for quenching is made by the sword maker through a combination of sensations such as "fire color," "blade luster," and "metallic sound." While this could be put into words, the verbalized information does not transmit with sufficient precision to be useful in actual work, so the form of kuden — causing apprentices to "embody" the technique — is adopted.
• Selection by Iron "Touch": The technique of judging carbon content by touching the cross-section of a fractured tamahagane can only be mastered through the accumulation of sensory experience. While it is possible to provide a verbal explanation such as "high-carbon tamahagane is hard and has a fine cross-section," one does not reach the level of "understanding" without actually touching it thousands of times.

The Social Function of Hidensho — For Whom Were They Written?

Considering for whom hidensho were written is important for understanding the nature of their contents.

• Notes for Successors: Personal records written by aging sword makers to leave their techniques to their successors. These may contain relatively detailed technical information.
• "Formal Records" of a School: Documents created to prove the legitimacy of a school, where the primary purpose may be to record the lineage — "from whom to whom it was transmitted" — rather than technical details.
• Disinformation to Counter Rival Schools: Historically, it is also said that hidensho containing "intentionally false information" existed. Some information was deliberately altered so that even if acquired by rival schools, it would be useless.
• Tool for Legitimacy: There are cases where hidensho themselves functioned as tools to give the impression that "this school has deep secrets." The possession of hidensho was proof of a school's authority, and its existence was more important than its contents.

Recording from the Meiji Period Onward — Recovery of Lost Techniques

The dramatic decrease in sword makers due to the Sword Abolition Edict (1876) and the dispersal of techniques due to the military sword production boom in the early Showa period had serious effects on the transmission of both hidensho and kuden.

In the postwar revival of Japanese sword culture, the NBTHK (Japanese Sword and Art Sword Preservation Society) undertook a project to document techniques. Efforts were made to collect technical information from aging sword makers and record it as video, photographs, and documents. In this process, some techniques that had previously been considered "kuden only" were put into writing for the first time.

In modern times, a format called "video kuden" has also emerged. This is a method in which the master's actual work is filmed and apprentices repeatedly view the video while learning the technique. As something that complements and expands the traditional master-apprentice relationship form of "learning by watching," it is being utilized among younger sword makers. Techniques preserved through such recording efforts are inherited by today's sword makers and lead to sword creation.

Summary — The Philosophy of Transmission and Modern Challenges

The most important aspect of technical transmission in Japanese sword making lies in the philosophy of choice regarding "what to verbalize and what to allow to be embodied." Hidensho are records of "techniques that can be verbalized," while kuden is a mechanism that promotes the embodiment of "techniques that cannot be verbalized." This two-layered structure was the knowledge management system that has maintained and advanced sword maker techniques over centuries.

The modern challenge is the simple fact that "if there are no successors, kuden will be lost." No matter how detailed hidensho may be, true technique cannot be transmitted without actually seeing the master's hands, hearing the master's words, and experiencing striking iron at the master's side. The essence of technical transmission lies not in documents but in the relationship between people — this fact is a fundamental starting point for considering modern sword maker protection policies.