The System of Smithing Tools: How Hammers, Anvils, Bellows, and Quenching Water Define the Swordsmith's Craft

Tools Define Technique—The Significance of Swordsmith Tool Theory

There is a saying "A master does not choose the brush," but in the forging of Japanese swords, "the swordsmith chooses the tools." The better the swordsmith, the stronger their commitment to their own tools, and the selection, adjustment, and self-creation of tools become part of their technique.

Each stage of the Japanese sword forging process—heating tamahagane, forging, shaping, and quenching—requires specialized tools. These tools are not mere "equipment" but a precise system of tools embodying the swordsmith's technical philosophy. The tool configuration of the entire workshop is also covered in detail in Swordsmith Tools and Workshop Equipment Composition.

Hammer (tsuchismith)—The Star Role in Shaping Steel

Large Hammer (ootsuchi)—Creating the Framework

The ootsuchi is a heavy hammer used in the early stages of the forging process. It plays a central role in forging and folding tamahagane, performing fold-forging, and creating the rough outline shape of the sword blade (sonobeashi).

Weight: The weight of the ootsuchi is typically 2–5 kg. The preferred weight varies depending on the swordsmith's physique and forging style.

Materials: The head is typically made of steel, and the handle of wood (magnolia or chestnut). The balance between the hardness of the steel in the head and the hardness of the anvil is important—a hammer that is too hard will damage the steel, while one that is too soft will lose efficiency.

Role of the Senior Apprentice (saki-deshi): In traditional forging shops, a division of labor takes place where the master (swordsmith) sets the rhythm with a small hammer while the apprentice (saki-deshi) swings the large hammer downward. The master's small hammer shows "where to strike," and the apprentice's large hammer applies force to that location. This "unity of breath" determines the efficiency and quality of fold-forging.

Small Hammer (kodzuchismith)—The Tool of Precision Shaping

After the large hammer creates the rough shape, the small hammer is used for precise shaping. The swordsmith directly holds it by hand to refine the details.

Weight: Typically 500g–1.5 kg.

Diversity of Shape: The small hammer varies in shape depending on its purpose. Different hammers are used depending on the shaping required for each part of the sword (tip, ridge, and neck).

• The "flat hammer (hira-tsuchismith)" with a flat surface
• The "square hammer (kaku-tsuchismith)" with an angled edge
• The "round hammer" with a rounded surface

Wooden Hammer (kidsuchi)—Collaboration with Scabbard and Handle Makers

Wooden hammers are used to refine shape without striking metal directly. They are also used by the handle-wrapping craftsman when applying shagreen skin and by the polisher when applying whetstones.

Anvil (kanakoko)—The Foundation that Receives Steel

Function of the Anvil

The anvil is the platform that receives the steel struck by the hammer. Throughout the entire forging process, steel is worked on top of the anvil.

Materials: Anvils are generally made of steel, but the surface hardness (the degree of quenching) is critical. If too hard, the steel easily becomes damaged; if too soft, the anvil itself deforms.

Weight and Stability: The heavier the anvil, the more stable it is. A light anvil moves with the impact of the hammer, making precise shaping difficult. In large forging shops, anvils weighing 100 kg or more are sometimes used.

Anvil Shapes

• Flat-face type (heimengata): The most basic shape. A wide flat surface supports the steel.
• Horn-type (horn type): One or both ends have protruding "horns" (corners). Bending and fine shaping can be performed on the horns. Used for shaping the curve of the tip.
• Grooved type (mizotsugikata): An anvil with grooves carved into the surface. When shaping rod-shaped material, it is placed in the groove for stability.

Bellows (fuigo)—The Tool of Wind that Controls Flame

Function and Principle of the Bellows

The bellows (fuigo) is a air-supply device that sends air (oxygen) into the furnace (kamado). Forced air-supply to fuel (primarily charcoal) is necessary to heat iron to a workable temperature (800–1200°C). The technique of reading this temperature by color is separately systematized as The Art of Fire Color Judgment.

Traditional bellows are called "box bellows (hako-fuigo)," a wooden box-shaped air-supply device. Inside the box is a piston-like board (fuigo-ita), which is moved back and forth to push out air.

Management of Air Flow—The True Nature of "Adjusting the Fire"

The volume of air supplied to the furnace directly controls the heating temperature of the steel. More air (strong air-flow) raises the temperature, while less air (weak air-flow) lowers it. The swordsmith adjusts this air volume by the speed of the bellows, observing the color of the steel (red-hot, yellow-hot, white-hot) to judge the appropriate temperature.

"Observing the fire condition" actually refers to the combined management of bellows operation (air volume) and fuel placement in the furnace (amount and arrangement of charcoal).

Modern Bellows

In modern forging shops, electric blowers are common. They stabilize air volume more easily than manual box bellows and reduce the physical exertion of apprentices. However, some smiths maintain traditional box bellows, saying "electric cannot achieve the subtle control of the bellows."

Quenching Water (yakimizu)—The Sacred Water of Quenching

The Role of Quenching Water in Quenching

"Quenching (yakiire)" is the most critical process in creating Japanese swords. When a white-hot sword blade is rapidly cooled in water (yakimizu), the edge portion (high-carbon area) undergoes martensitic transformation, creating a hard edge.

The water used for this rapid cooling is "quenching water (yakimizu)." The water quality, water temperature, and material of the container (water tank) of the quenching water greatly affect the result of quenching (the shape of the hamon, sharpness, and amount of curvature). The selection of the cooling medium itself is explored further in How the Choice of Quenching Liquid Determines the Hardness of the Blade.

Water Quality—The "Personality" of Water that Smiths Value

For Japanese sword quenching, "soft water (nansuismith)" is considered appropriate. Hard water (water with high mineral content) may affect rapid cooling efficiency.

It is recorded in many texts that swordmakers in historically renowned sword-producing regions (Bizen, Soshu, Yamashiro, etc.) valued water quality highly. The record that Bizen (Okayama) swordmakers valued "Asahi River water" is famous. Many modern swordsmiths still have preferences for local water, well water, or specific spring water.

Water Temperature—Management of Seasons and Time

The temperature of quenching water is generally considered to be "about body temperature (approximately 35–40°C)," but this varies by swordsmith.

Water temperature changes between winter and summer, so seasonal adjustment by heating or cooling may be necessary. The reason it is said that "quenching is difficult in winter" is that when the water temperature is too low, the efficiency of rapid cooling changes, increasing the risk of cracking (quench cracks).

Water Tank (mizuoke) Material

The container holding the quenching water is also a matter of individual swordsmith preference. Wooden buckets (oke) are traditional, but wood has the property of gently retaining heat. In modern times, metal and plastic water tanks are also used, but some smiths insist on wooden buckets.

The Forge (kajiba)—Space That Brings Out Tool Potential

Furnace Placement and Direction

The position of the furnace (combustion device) is the core of forge design. The spatial relationship among the furnace, anvil, and quenching tank is designed so the swordsmith can work with maximum efficiency during forging.

The relationship between furnace direction (direction of flame) and light (natural light) is also important. Since the swordsmith reads the color (temperature) of the steel visually, a forge with proper access to natural light and flame light is necessary.

Temperature and Humidity Management

The air temperature and humidity of the forge also affect forging. Particularly in the quenching process, ambient temperature affects the quenching water temperature, so work planning must account for the season. This is why many swordsmiths have the custom of concentrating quenching operations in winter.

Conclusion—Tools Are the Swordsmith's "Second Hand"

Japanese sword forging is a place where the swordsmith's "eyes," "ears," "hands," and "intuition" are applied with full force. But for those senses to function, the tools supporting them must be precisely aligned.

The appropriately weighted hammer, the accurately flat anvil, the bellows that can delicately adjust air volume, the quenching water of optimal quality and temperature—only when all these are in place does the swordsmith's technique finally take form in the blade.

To know the tools is to know the swordsmith's work. The hammers and anvils lined up in the forge are not mere lumps of metal, but the physical foundation of a precise technical system that produces the artwork that is the Japanese sword.