Quality Inspection by Swordsmiths: From Visual Check to Test Cutting

Where Does a Bladesmith's Work End?

A bladesmith's work is often thought to be "hammering steel at the forge," but in reality, significant tasks remain after the forging process is complete. After quenching (yaki-ire) and tempering (yaki-modoshi) are finished, the blade undergoes initial polishing called rough grinding (ara-togi), which the bladesmith performs personally before handing it over to a specialized polisher (togishi). However, before this handover, the bladesmith performs one of the most important tasks: "final inspection" (metoshi).

Metoshi is the process of carefully examining the finished blade under light from every angle. While it is a visual inspection with the naked eye, a skilled bladesmith's gaze can detect minute defects that even X-ray inspection might miss. This article provides a detailed explanation of what the bladesmith sees and judges during this final inspection.

The Technique of Metoshi—Light and Angle Tell Everything

Metoshi typically involves holding the blade in hand and examining it from various angles against light sources such as windows or electric lights. The type of light source used determines which defects can be detected.

The bladesmith combines these light sources and examines the blade repeatedly from top to bottom and from face (omote) to back (ura). The time required for this work varies from five minutes to over an hour depending on the blade and the bladesmith's level of skill and the nature of the blade.

Types of Forging Defects—The "Crack" That Bladesmiths Most Fear

Defects discovered during metoshi fall into several types, each with varying severity and causes.

• Crack (wari): Internal cracks can develop in the blade due to temperature control failure during forging or internal stress from rapid cooling during quenching. To the naked eye, it appears as a small line, like the tip of a needle, but it is a serious defect that can lead to fracture and breakage when the blade is used. Among the defects discovered during metoshi, this is considered the most severe.
• Skin roughness (hada-are): This refers to a rough and coarse state of the forge grain of the steel due to insufficient forging or uneven heating. It not only damages appearance but also affects strength.
• Edge chipping (ha-kobore): These are minute chips in the edge that occur during post-quenching processing or rough grinding. The severity varies from damage that can be corrected through main polishing (hon-togi) by the polisher to deep damage that requires repair by the bladesmith.
• Curvature deviation (sori no kurui): This is one of the most common problems that occur during quenching. If the curvature deviates from the designed amount, the bladesmith performs correction immediately after quenching (while the blade is still relatively flexible). This work is a delicate process that depends on the craftsman's intuition and experience.

Rough Grinding and the Bladesmith's Scope of Responsibility

After metoshi, the bladesmith often performs rough grinding (ara-togi). Rough grinding is the process of shaping the blade using a coarse-grit whetstone (toi-shi) and removing surface irregularities from forging. At this stage, detailed finishing of the hamon is not performed; it remains purely "groundwork preparation before handing over to the polisher." For the full polishing process with finer stages that bring out the hamon, see Shinogi-ji and Hiraji Polishing Technique for detailed information.

Through rough grinding, the bladesmith makes a final check to ensure that the blade's shape (sugata, nari) is finished according to design intent. The bladesmith checks measurements of base width (moto-haba), tip width (saki-haba), and thickness (kasane) to verify that the blade meets the ordered specifications. From a quality control (QC) perspective, this process amounts to a "final inspection."

Some bladesmiths have the practice of not performing rough grinding and handing over the blade in its as-forged state to the polisher. In that case, the polisher handles the rough grinding, but communication between the bladesmith and polisher becomes even more important.

Test Cutting—Final Confirmation of Practical Performance

Not all bladesmiths do this, but there is a practice of confirming the finished blade (after polishing) through test cutting. Test cutting is often performed by polishers or sword merchants, but bladesmiths sometimes perform it themselves to confirm their work's sharpness and durability.

Modern test cutting primarily uses bundles of tatami covering (also called maki-wara) or tatami with bone. Through test cutting, what is confirmed is the edge's "sharpness (kire)"—the lack of resistance during cutting—and the blade's "rigidity (gousei)"—the strength that resists deformation and breakage from impact.

If the sharpness is insufficient, it leads to additional requests to the polisher or a review of the steel composition by the bladesmith; if there are problems with durability (particularly if cracks or deformation occur), the blade is discarded as a failure. For modern bladesmiths, discarding a blade represents a significant economic loss, but releasing defective goods to market is strictly self-regulated as a matter of craftsman honor.

The Philosophy of Craftsmanship That Metoshi Conveys

The process of metoshi and quality inspection is not merely a task of defect discovery. It is also a philosophical moment when the bladesmith answers for themselves the question, "Is this blade worthy of being released into the world?"

In traditional sword philosophy, a blade with defects is described as "not truly alive as a blade." The idea is that only when all processes—the tamahagane material, the forging technique, the quenching temperature control—are perfectly layered does a blade receive its "life" as a true sword. Metoshi is the act of confirming that life, and it is the final chapter of the bladesmith's solitary and solemn work of confronting their own skill.