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Articles on tamahagane, quenching, polishing, and lacquer — the technique and science behind the blade.
In nihonto forging, the swordsmith's ko-zuchi (small hammer) and the assistant's o-zuchi (large hammer) work in concert to shape the steel. This article explains how hammer weight, shape, and technique affect the forging process.
茎の末端「茎尻」には栗尻・剣形・入山形などの形があり、刀工の流派や時代を映す。茎尻の整形と化粧鑢の意味、鑑定上の役割を技術の視点から解説する。
折り返し鍛錬で鋼を接合する鍛接には、藁灰と泥汁が欠かせない。これらが酸化を防ぎ不純物を流す仕組みと、刀工が振りかけるタイミングを化学の視点から解説する。
日本刀の研磨は段階ごとに異なる砥石を使い分ける。荒砥・中砥・内曇砥といった天然砥石の種類と性質、刃艶・地艶に用いる仕上げ砥の役割を解説する。
刀身に彫られる「樋」は軽量化と装飾を兼ねる。棒樋・二筋樋・腰樋などの種類、樋を掻く道具と工程、樋先の処理に表れる技術を解説する。
刃部だけでなく地にも焼きを散らす「皆焼」は、土置きと焼き入れの高度な制御を要する刃文である。相州伝に始まるこの技法の作り方と難しさを解説する。
丁子刃にはさらに洗練された数珠刃・重花丁子といった変化形がある。揃った頭や二重に咲く花の景色をどう焼き出すのか、備前伝の高度な焼き分けを解説する。
切先に現れる刃文「帽子」は、焼き入れで最も失敗が許されない箇所である。土の置き方や冷却の難しさ、焼き詰め・小丸など帽子の姿を決める技術を解説する。
江戸時代、刀工は南蛮鉄と呼ばれる輸入鉄を作刀に取り入れた。和鉄との性質の違い、鍛え方の工夫、銘に記された「以南蛮鉄」の意味を技術の視点から解説する。
折り返し鍛錬に入る前、玉鋼は水減しと小割りという下準備を経る。塊を平たく延ばして割り、炭素量や質を見極めて選り分ける刀匠の最初の判断を解説する。
たたら製鉄には鉧押しと銑押しという二つの操業法がある。それぞれ何を主産物とし、玉鋼がどのように得られるのか、温度や炭の使い方の違いを含めて解説する。
An explanation of the mechanisms behind yakiware (quench cracking) and hiwari (fire cracking) caused by phase transformation during quenching, along with prevention techniques and remediation practiced by swordsmiths.
Comparing nihonto forging with kitchen knife and farm tool smithing — shared steel-working principles and the unique demands of tamahagane, clay-quenching, and aesthetic excellence.
This article provides a scientific explanation of blade patterns, detailing how two contrasting particle states—nie (coarse-grained) and nioi (fine-grained)—influence the appearance of the hamon, and how different sword-smith schools have historically used them distinctly.
A scientific examination of the bellows (fuigo) and furnace temperature control at the heart of Japanese sword forging, exploring how charcoal type, airflow, and heating duration affect tamahagane carbon content and blade quality.
An explanation of the role of 'tacit knowledge' (bodily knowledge) in Japanese sword forging that cannot be conveyed through text, numbers, or diagrams. Explores the reality of the sensory judgments swordsmiths engrave into their bodies through years of experience—such as reading fire color (hiiro), sensing the right moment to strike (uchigoro), and judging the state of iron by sound—and how this is transmitted through the apprenticeship system.
An explanation of how swordsmiths communicate their artistic vision to polishers and the polishing philosophy with which polishers respond.
A scientific explanation of why Japanese swords develop their characteristic curve (sori), examining residual stress, martensitic transformation, and differential cooling rates.
A detailed explanation of how tamahagane steel produced by tatara smelting is graded and sorted into kawagane and shingane based on carbon content and quality.
A detailed explanation of the raw materials, mixing ratios, and preparation process for the clay coating applied before quenching, with analysis of how clay properties shape hamon patterns.
A detailed guide to forge-welding in the warikomi construction method, where swordsmiths wrap core steel in skin steel inside the furnace. Covers temperature control, judging the right moment to strike, and modern smiths' techniques for preventing weld failures.
A technical explanation of ji-nie (fine martensite particles scattered across the blade surface), covering the role of carbon concentration distribution in martensite formation, the relationship to clay coating patterns, how strong versus faint ji-nie affects appraisal value, and the aesthetics of the nie-deki style exemplified by Soshu-den swords.
The lacquer arts applied to Japanese sword mountings—vermilion, aogai shell inlay, and ikakeji gold-powder ground—are among the most refined decorative crafts in Japanese art history.
Tsumiwakashi, the process of stacking and forge-welding multiple tamahagane pieces, is the foundational step before folding in Japanese swordmaking. This article examines the science and artisan intuition behind this critical process.
In Japanese swordsmithing, there are no thermometers. The smith must read the color of the glowing steel and forge fire by eye alone to judge whether the temperature is optimal. This article explains the system of fire-color reading and how this skill is trained.
In Japanese swordsmithing, the smith may perform a quality-checking process called tameshi-uchi before final completion. This process verifies the homogeneity of the steel, the shape before quenching, and the quality of forging, serving as an early detection method for potential failures. This article details the process and judgment criteria.
The inscriptions carved into a uchigatana's nakago represent a vital record of a swordsmith's technical pride and social standing. Tracing the evolution from simple Muromachi-era place names and smith names to the elaborate date inscriptions, dedication inscriptions, and commission inscriptions of the Edo period reveals the deeper history of Japanese sword culture.
Yakihaba refers to the width of the tempered zone as it extends from the edge toward the spine after quenching. Controlling this width is one of the supreme tests of a swordsmith skill, determined by clay thickness and water temperature during quenching. This article explains the characteristics and control techniques of shallow and deep quenching.
Hizukuri is the forging process that shapes the basic form of a Japanese sword. The heating temperature and hammer timing in the forge determine the blade's shape, curvature, and profile. This article explains how swordsmiths read heat and wield hammers.
A scientific explanation of how Japanese sword curvature (sori) is formed during the quenching process, covering martensite transformation-induced volume changes, thermal stress, clay coating pattern effects, post-quench correction techniques, and how curvature shape affects practical performance.
A metallurgical primer for understanding nihonto: ferrite, pearlite, and martensite microstructures explained in the context of swordmaking, quenching, and folding techniques.
An examination of the two-stage division of Japanese swordmaking labor between okaji (steel refinement) and kokaji (blade forging), its historical roots, technical significance, and modern changes.
A scientific explanation of the oroshigane process by which swordsmiths refine tamahagane steel, covering slag removal, carbon homogenization, and impurity elimination from the perspective of modern metallurgical science.
