Tamahagane and Tatara Smelting — 1500-Degree Direct Reduction from Okuizumo

Why Must a Japanese Sword Be Made from Tamahagane?

The material used for the kawagane and shingane described in the previous article ([Structure of the Japanese Sword]) is collectively called tamahagane. It is not the uniform industrial steel of modern blast or electric furnaces, but a special steel made by an ancient direct-reduction method: tatara smelting. Why go through this laborious process? Two reasons:

1. Extremely low levels of impurity (phosphorus and sulfur) — the greatest enemies of steel toughness are avoided both in the raw material and in the process
2. A spread of carbon content — a single kera (bloom) contains both high- and low-carbon regions in one piece, so the smith can adjust it by hand to the target carbon level

Modern electric-furnace steel controls impurities strictly but has such uniform grain structure that the “landscape” of the jihada does not appear. The very unevenness of tamahagane is what produces its aesthetic and functional value — a peculiarity of the Japanese sword.

Tatara Smelting — A Form of Direct Reduction

Tatara is a native Japanese smelting technique that directly reduces iron sand and charcoal at low temperature to obtain steel. The word itself derives from the large, foot-operated fuigo (bellows), and by extension came to mean the smelting furnace and the entire smelting operation.

Contrast with modern blast smelting:

	Modern blast furnace	Tatara
Raw material	Iron ore	Iron sand
Reductant	Coke (coal)	Pine charcoal
Furnace temperature	~1500 °C and above	~1200-1400 °C
State	Iron melts	Semi-molten (does not melt)
Product	Pig iron → converted to steel in a separate step	Steel produced directly in one operation

In tatara smelting, iron does not melt but is reduced in a granular state and collects at the bottom of the furnace, gradually forming a large mass (kera). Because operation is at low temperature, impurity uptake is minimal — and steel is obtained in a single run.

Masa Iron Sand — The Gift of the Chūgoku Mountains

The raw material for tatara is iron sand, of which there are two main types:

• Masa iron sand (masa-satetsu) — Granite-derived. Low impurities, high quality. Distributed across the Chūgoku mountains (Shimane, Tottori, Okayama, Hiroshima). Tamahagane for Japanese swords is made almost exclusively from this masa sand.
• Akome iron sand (akome-satetsu) — Derived from diorite/gabbro. Contains titanium and has a lower melting point. Suited to cast iron (zuku); of lower quality for swords.

The Chūgoku mountains excel as an iron-sand region because of their geology (weathered granite) and their river terrain suited to kanna-nagashi — a sorting technique in which mountains are cut down to release iron sand. Okuizumo in Shimane remains the sole source of tamahagane for Japanese swords into the present.

Kanna-nagashi involves massive land alteration, and the topography of the Chūgoku range was profoundly changed by it. Large amounts of sediment washed into downstream rivers, forming what is called kanna-taiseki (“kanna deposits”). This is also a subject of study in ecology and geography.

An Operation — Seventy-Two Continuous Hours

A single operation is called hito-yo (“one night”). About 72 hours of continuous work.

Building the furnace

The tatara furnace is a clay-based box, roughly 3 m long, 1 m wide, 1 m deep. Below it is a subterranean structure called the hondoko, where charcoal is burned for months to dry it and cut off moisture. On the hondoko, a clay furnace is built with haguchi (tuyeres) — air holes — on both sides.

The furnace is destroyed each operation (without destroying it, the kera cannot be extracted), so it is rebuilt from scratch every time. The person responsible is the technical chief, the murage.

From lighting to kera extraction

• After lighting, the murage directs the alternating input of iron sand and charcoal
• Several kilograms per input, at intervals of about 30 minutes, roughly 60 times in total
• The bellows are worked in pairs by the banko, in shifts that never stop
• One operation consumes roughly 13 tons of iron sand and 13 tons of charcoal, yielding about 2.8 tons of kera (a yield of ~20%)
• Operation is normally in winter (November through the following March), when lower temperature and humidity make it easier to keep the furnace interior hot

Progress is judged by the color of the smoke, the sounds, and the state of the incandescent iron. Experience and intuition are everything. The murage’s technique was passed down through hereditary apprenticeship.

Removing and cooling the kera

After 72 hours, the furnace is destroyed and the red-hot kera is extracted, then rapidly cooled with water. That closes the operation.

Kera and Grading

The kera formed inside the furnace is heterogeneous. The center is high-carbon and hard; the periphery is low-carbon and soft. After cooling it is broken up with a great hammer, and the cross-sections are inspected and graded:

• First-grade tamahagane — Bright white, dense. Highest grade, for swords
• Second-grade tamahagane — Slight color, but good quality
• Mejiro — Just below tamahagane
• Koro-kera — Middle grade for sword use
• Zuku (pig iron) — High-carbon and brittle. For casting and farm tools
• Buke-ra — Softer iron, low carbon

The smith buys graded steel and separates it for use as kawagane or shingane. Tamahagane is generally 1.0-1.5% C; through fold-forging it is worked down to the 0.6-0.8% needed for kawagane.

The People — Iron Merchants and the Murage

Tatara operations were run by wealthy merchants called tesshi. Well-known families in Izumo include the Itohara, Tanabe, and Sakurai. Beneath them:

• Murage — Technical chief. Hereditary
• Sumisaka — Head of charcoal burning
• Banko — Laborer at the bellows
• Yamako — Wood-cutters
• Kanna-shi — Iron-sand miners

Large tatara sites employed hundreds of workers as an organized community.

Kanayago-no-kami and the Ban on Women

Every tatara site enshrined Kanayago-no-kami, the deity of iron. Because tradition holds this deity to be a jealous goddess, tatara sites were historically closed to women. Ironically, modern tatara revival projects include many women researchers.

The tatara site of Lady Eboshi in Miyazaki Hayao’s [Princess Mononoke] is modeled on these folk elements. Cutting down mountains, burning forests, making iron — the environmental cost, and the distinctive belief and community that supported it.

The Present Supply — The Nittōho Tatara

From the Meiji period on, the spread of modern iron making meant that tatara was nearly extinguished. But because of the material’s central importance to the Japanese sword, in 1977 the Nippon Bijutsu Tōken Hozon Kyōkai (Nittōho) rebuilt the Nittōho tatara in Okuizumo, Shimane.

• Operates several times a year in winter
• Nearly every present-day Japanese sword-smith uses tamahagane from the Nittōho tatara
• Public viewing is available on select days
• Current murage include Kihara Akira and Dōmoto Terusuke, from the small circle of hereditary and adopted successors

It is the only place in the world producing tamahagane for Japanese swords. If it were to end, modern smiths would lose their material.

From This Article to the Next

We have traced the material and its smelting. But what happens between tamahagane and a finished blade? The next article turns to the fire-craft of the smith — fold-forging and quenching. Steel forged 15 to 30 times, edges rapidly cooled at over 1000 °C, and the resulting hamon and curve. From materials science to craft science, we enter the heart of the “how the sword is made.”