Tameshi-uchi: The Test Forging Process That Determines Blade Quality Before Completion

What is Tameshiuchi? — Quality Confirmation Before Completion

"Tameshiuchi" (試し打ち) is commonly understood to mean "tameshigiri" (試し斬り)—testing the cutting ability of a completed blade. However, in the context of forging technique, the term can also refer to "experimental striking" or "sample forging" performed during production to confirm the state of the blade material. This article explains the latter meaning—tameshiuchi as an "intermediate check" in the blade-making process.

The intermediate confirmations a swordsmith performs at each stage of forging can be broadly classified into three types: "visual confirmation," "confirmation by hammer feel," and "trial cutting (checking for peeling and cracks)." The consolidated concept of these methods is "tameshiuchi," and because defects discovered after completion are difficult to repair, this process determines the success or failure of blade making.

Confirmation After Folding Forging — Early Detection of Hadaware and Cracks

After performing folding forging several times, the swordsmith carefully observes the steel surface. The main thing to check at this point is the presence or absence of "hadaware" (肌割れ)—skin cracks.

Hadaware are fine cracks that develop in areas where the temperature was too low during folding forging, areas where the steel had many impurities, or areas where the fold adhesion was incomplete. Small hadaware may disappear through continued forging, but deep cracks do not resolve even with repeated forging and ultimately remain as blade defects.

One confirmation method at this stage is "applying light striking and observing how cracks spread." The steel is reheated to an appropriate temperature, and the surface changes and presence or absence of peeling when struck lightly with a hammer are observed. If the cracks spread, the material is judged to have a problem, and in some cases, the decision is made to restart from the material. While this involves significant cost, it is a far more rational choice than discovering defects after completion.

Trial at the Sunobe Stage — Shape Uniformity Check

Once the folding forging ends and the swordsmith enters the "sunobe" (素延べ) stage of creating the basic blade form, a different type of confirmation becomes necessary. The purpose of tameshiuchi at this stage is to confirm "uniformity of blade thickness" and "uneven carbon distribution."

Blade thickness uniformity is confirmed by actually bending the blade lightly. If there is a part that has become too thin, that part will deform first and can be confirmed visually. The unevenness of carbon distribution can also be judged from changes in hammer feel (the difference between parts that feel soft and parts that feel hard). High-carbon areas are relatively hard, while low-carbon areas have a softer feel. The main goal of the sunobe stage is to eliminate this difference in feel and homogenize the overall blade.

Confirmation After Hidzukuri Completion — Comprehensive Assessment of Curvature and Shape

After the "hidzukuri" (火造り) stage that shapes the blade outline is completed, a final shape confirmation before hardening takes place. The "tameshiuchi" at this point can be reframed as "checking the shape in anticipation of temporary hardening."

The swordsmith simulates in advance how the blade will curve (develop curvature) from hardening and intentionally creates shallow curvature (or reverse-direction curvature) at the completion of hidzukuri. To confirm whether this shape design that anticipates post-hardening deformation is correct, the swordsmith sometimes performs temporary hardening on similar-shaped material to measure the amount of deformation. This is sometimes called "tameshiyaki" (試し焼き).

The deformation measurement data obtained from this trial hardening becomes the basis for fine-tuning the hidzukuri shape before the actual hardening. Experienced swordsmiths memorize this deformation amount from their vast past forging experience, but trial hardening is essential when using new materials (such as tamahagane from different batches).

Differences from Ancient "Tameshimono" (Trial Swords)

Trial forging during blade making is fundamentally different from "tameshimono" (試し物)—testing the cutting ability of a completed blade. Tameshimono was an Edo-period institutional practice using the bodies of executed criminals, bundles of grass, water-filled bamboo, and similar materials to quantify cutting ability, and its purpose was the "grading" of sharpness.

In contrast, trial forging during blade making aims at early detection of defects and quality assurance, and is a quality control activity embedded in the manufacturing process, not post-completion evaluation. This concept corresponds to the modern manufacturing practice of "in-process inspection," and is a fine example of the emergence of modern quality management thinking within Japanese craftsmanship.

The Reality of Tameshiuchi Among Modern Swordsmiths

Modern swordsmiths are restricted by law to produce a maximum of 24 blades per year (the limit per officially recognized swordsmith by the Agency for Cultural Affairs), and a single failure represents a loss equivalent to approximately 4.2% of annual production. Therefore, the importance of intermediate confirmation remains high even in modern times.

Many modern swordsmiths adopt the technique of extracting sample pieces (steel scraps) at each stage of folding forging, polishing them, and visually confirming the structure of the ground steel. By confirming the uniformity of the grain patterns (mokume, itame, masame) that appear when the steel is polished, the quality of the forging can be assessed. This can be said to be a quality management technique that represents a modern interpretation of traditional "tameshiuchi."

Summary — Tameshiuchi as a Craftsman's Self-Dialogue

Tameshiuchi is the act of a craftsman questioning their own work. "Is this steel uniform?" "Is this shape suitable for hardening?" "Are there defects in this material?"—The process of finding answers to these questions is tameshiuchi, and it is a moment when the swordsmith's integrity and technical skill are tested. Behind the beauty of the finished product lies an accumulation of careful confirmation work in these invisible processes.