Quality Inspection by Swordsmiths: From Visual Check to Test Cutting

Where Does the Sword Smith's Work End?

The work of a sword smith is often thought to be "forging a sword at the forge," but in reality, important tasks remain even after the forging process is complete. After quenching (yakiire) and tempering (yakimodo) are finished, the blade undergoes an initial polishing process called rough polishing (aratohi), which the sword smith performs himself before handing it over to a specialized polisher (togishi). But before this handover, the sword smith performs one of the most important tasks: "eye examination" (metoshi).

Metoshi is the work of holding the finished blade up to light and carefully examining it in its entirety. Though it is a visual inspection by the naked eye, the trained eye of a master sword smith can detect minute defects that even X-ray inspection might miss. This essay will provide a detailed explanation of what the sword smith observes and judges at this final inspection.

The Technique of Metoshi—Light and Angle Tell All

Metoshi generally involves holding the blade in hand and viewing it from various angles against light sources such as windows or electric lights. The type of defects that can be detected varies depending on the type of light source used.

Fluorescent lights and LED lighting are suitable for clearly showing the forging pattern (kitaeme) of the steel (jigane) and the boundary line of the hamon. They are used to check whether the hamon appears uniformly and whether the quenching produced the intended shape.

Natural light (overcast sky outdoors) allows for the most natural observation of the surface finish (hada) of the steel—such as itame, masame, and mokume patterns. It reveals whether the forging finish is uniform and whether there are any forging variations or "iron oxide stripes (shima)."

Point light sources such as candles or light bulbs are used to check the "curve" (sori) and "bending" (magari) of the blade. By moving the point light source away while viewing the blade in a straight line, subtle curvature and asymmetry between left and right become visible.

The sword smith uses these various lights in combination, examining the blade repeatedly from top to bottom and from front to back. The time required for this work varies from five minutes to more than an hour, depending on the expertise of the sword smith and the characteristics of the blade.

Types of Forging Defects—The "Crack" That Sword Smiths Fear Most

Among the defects discovered during metoshi, the most serious is "cracking" (ware). Minute cracks may form in the blade due to failures in temperature management during forging or internal stress caused by rapid cooling during quenching. Though it appears as a tiny line barely visible to the eye on the surface, it is a serious defect that can lead to breakage if the sword is used.

Next is the issue of "surface roughness" (hadaare). This refers to a coarse and rough condition of the forging finish caused by insufficient forging or uneven heating. It not only affects aesthetics but also impacts strength.

"Edge chipping" (habokore) refers to minute chips on the edge that occur during post-quenching treatment or rough polishing. These range from minor chips that can be corrected by the polisher during final polishing (hontogi) to deeper damage requiring repair by the sword smith.

"Curvature deviation" (sori no kurui) is one of the most common issues that occur during quenching. If the curve deviates from the design specification, the sword smith corrects it immediately after quenching, while the blade is still relatively flexible. This is a delicate process that depends on the craftsman's intuition and experience.

Rough Polishing and the Sword Smith's Area of Responsibility

After metoshi, the sword smith often performs the rough polishing (aratohi) himself. Rough polishing is the process of using coarse whetstones (toishi) to shape the blade and remove surface irregularities from forging. At this stage, detailed hamon finishing is not performed; it is strictly preparation before handing the blade to the polisher.

Through rough polishing, the sword smith performs a final check to confirm that the blade's form (sugata, nari) has been finished according to design intent. He verifies measurements of the base width (motohaba), point width (sakihaba), and depth (kasane) to ensure the blade meets the specifications of the order. From a quality control perspective, this process is equivalent to "final inspection."

Some sword smiths do not perform rough polishing and instead hand the blade to the polisher in its as-forged state. In such cases, the polisher handles the rough polishing, but communication between the sword smith and polisher becomes even more important.

Test Cutting—Confirming Final Practicality

Though not all sword smiths do this, there is a practice of confirming the finished blade (after polishing) through test cutting. While test cutting is often performed by polishers or sword merchants, sword smiths sometimes perform it themselves to verify the cutting performance and strength of their work.

In modern test cutting, bundles of tatami mat surface (also called "makiwara") or tatami with bone are primarily used. What is confirmed through test cutting is the edge's "cutting ability" (kire)—the lack of resistance during cutting—and the blade's "rigidity" (gousei)—its strength against deformation or breakage under impact.

If the edge is insufficiently sharp, it may lead to additional requests to the polisher or a review of the steel composition by the sword smith; if there are strength issues (especially cracks or deformation), the blade is discarded as a failure. For modern sword smiths, discarding a blade represents significant economic loss, but releasing a defective blade to market is strictly self-regulated as a matter of personal honor.

The Craftsmanship Philosophy Behind Metoshi

The process of metoshi and quality inspection is not merely a matter of finding defects. It is also a philosophical moment when the sword smith must answer his own question: "Is this blade worthy to be released into the world?"

In traditional sword philosophy, a blade with defects is said to be "not alive as a sword." The philosophy is that only when all processes—from the tamahagane material to forging technique to quenching temperature control—stack perfectly can a blade be "breathed to life" as a true sword. Metoshi is the act of confirming that life, and it is the final chapter of the solitary and solemn work in which the sword smith confronts his own skill.