Tosa Blades: The Free-Forged Knives of Kochi

Sakai made its name with the professional chef’s knife, Seki with the sword, Echizen with the farmer’s sickle. Tosa made its blades for the mountain. Kochi — the old province of Tosa, on the Pacific side of Shikoku — is around 84 percent forest, the highest share of any prefecture in Japan, and for most of its history its smiths were making the axes, hatchets, saws and sickles that worked that forest. The kitchen knife came later, and it inherited everything those tools had to be.

Swordsmiths and field smiths

The craft’s own account starts with swords. In the Kamakura period — 1306 is the date usually given — swordsmiths of a school from Yamato province, present-day Nara, are said to have moved to Tosa. Their techniques gradually mixed with those of the local smiths who were already hammering out tools for farms and woodland.

By 1590 there were a lot of them. The Chōsokabe land survey, the register the ruling Chōsokabe clan compiled of their domain, lists 399 blacksmiths in Tosa.

The real growth came a generation later. In 1621 the Tosa domain launched what are known as the Genna Reforms, pushing to open new rice paddies and to make use of its huge forests. Clearing land and felling timber on that scale needs tools, and the smiths of Tosa supplied them. The blend that came out of this period — the sword smith’s obsession with an edge, the field smith’s insistence on something that survives hard use — is what Tosa blades are still known for.

Free forging: no mould, one pair of hands

The word that comes up every time Tosa blades are described is jiyū tanzō, “free forging.” There is no mould and no die. The smith heats the steel and shapes it with the hammer alone, which means the same forge can turn out a small kitchen knife in the morning and a long forestry blade in the afternoon, in whatever size and profile the customer asks for. Small runs, custom shapes and odd regional tools are exactly what the method is good at.

The other thing that sets Tosa apart is who does the work. In Sakai, a single knife passes through the hands of a forging smith, a separate sharpener and a merchant. In Tosa, one smith traditionally carries a blade through the whole process, from the fire to the finished edge.

That process runs roughly like this:

• Charcoal. The smith splits charcoal into even pieces so the fire burns at a steady heat. It is said to take three years just to get this right.
• Joining steel to iron. A strip of soft iron is split, and a piece of hard carbon steel is set into the groove and forge-welded in place. The hard steel becomes the cutting edge; the iron gives the blade its toughness.
• Forging. A mechanical belt hammer, developed in Kochi in the early Showa era and a big reason production rose in the 20th century, does the heavy drawing-out. The detail is still done by hand hammer.
• Mud and quench. The blade is coated in clay so it heats and cools evenly, brought to around 770–800°C and quenched in water, then tempered at about 170°C.
• Straightening and sharpening. Any warping is hammered out and the edge is ground and finished by hand.

Where it is made

Tosa blades come from a spread of towns across eastern and central Kochi — Kami, Nankoku, Kochi City, Susaki and others. The town most closely tied to the craft is Tosa-Yamada, now part of Kami City, which Shikoku’s tourism body describes as its birthplace; the smiths’ cooperative distribution centre is there.

In May 1998 Tosa uchihamono was designated a national traditional craft. The product list on that designation reads like a forester’s kit — axes, saws, sickles, hatchets, hoes — with kitchen knives among them rather than at the head.

Choosing a Tosa knife

A Tosa kitchen knife is built like a tool, and the best way to think of it is as one. You will often see them sold with a kurouchi, or “black-forged,” finish: the dark skin from the forge left on the upper part of the blade instead of being polished away, with only the bevel ground bright. It is a working finish, not a decorative one, and each blade looks slightly different.

Underneath, most traditional Tosa knives are hard carbon steel clad in softer iron, which means they take a very keen edge and will rust if left wet. Wipe and dry the blade after each use, and expect a patina to develop over time. Because free forging lends itself to small runs, it is also worth looking beyond the familiar gyuto and santoku — Tosa smiths make plenty of shapes that the bigger towns don’t.

Read: how Japanese knife steels differ, choosing your first Japanese knife and how to care for and sharpen it. For the other blade towns, see Sakai, Seki and Echizen. Or browse hand-picked, Japan-shipped blades on The Table.

Sources & Further Reading

• TOSA Uchihamono (Forged Blades) — Traditional Crafts Aoyama Square — The Association for the Promotion of Traditional Craft Industries on the craft’s history (the 1590 survey’s 399 smiths, the 1621 Genna Reforms), its integrated one-smith production, the belt hammer, and the May 1998 designation.
• Tosa Forged Blades (Tosa Uchihamono) — KOGEI JAPAN — The craft portal’s account of free forging, the production towns, and the step-by-step process from charcoal splitting to quenching at 770–800°C.
• Tosa Uchi-hamono knives — Tourism Shikoku — The Organization for Promotion of Tourism in Shikoku on the craft’s forestry roots, Tosa-Yamada in Kami City, and the Tosa blade distribution centre there.