Introduction

The hamon (刃文) is the distinctive temper line seen on Japanese swords, created during the yaki-ire (焼入れ, differential hardening process). It is one of the most visually striking and functionally significant aspects of a Japanese sword, as it reveals the boundary between the hardened cutting edge (martensite) and the softer, more flexible body of the blade (pearlite).

Hamon patterns are unique to each sword and serve as a signature of the swordsmith, showcasing their skill and school of training. Additionally, hamon can exhibit various internal activities (hataraki, 働き) such as kinsuji (金筋, golden lines), ashi (足, leg-like formations), and sunagashi (砂流し, sand-like streaks), which add to the artistic beauty and functionality of the blade.

This comprehensive guide explores the different hamon styles, their terminology, and the internal activities found within the hamon.

Formation and Purpose of the Hamon

The hamon is formed during yaki-ire (焼入れ), where the sword is:

  1. Coated with a special clay mixture (tsuchioki, 土置き) that insulates parts of the blade.
  2. Heated to approximately 750–850°C (1,382–1,562°F) in a forge.
  3. Quenched in water, causing the edge to harden while the spine remains softer.
  4. This results in a visible separation between hardened and softer steel, which forms the hamon.

The pattern of the hamon is determined by the way the clay is applied, and each swordsmith has their own distinct method, often influenced by their school of forging (ryū, 流派).

Types of Hamon Styles (Hamon no Katachi, 刃文の形)

Hamon styles can be broadly categorized into several groups, each with distinct characteristics and variations. Below is a list of documented hamon types, along with their descriptions.

1. Straight Line Hamon (Suguha, 直刃)

A simple and elegant hamon that follows a straight path along the edge. It is common in older swords (tachi from the Heian and Kamakura periods) and reflects refined craftsmanship.

  • Chu-suguha (中直刃) – A medium-width straight hamon.
  • Hoso-suguha (細直刃) – A thin straight hamon, often seen in delicate, refined blades.
  • Hiro-suguha (広直刃) – A wide straight hamon, giving a bolder appearance.

2. Wavy Hamon (Notare, 湾れ)

A gentle undulating hamon, resembling rolling ocean waves. It is common in Soshu-den and Bizen-den swords.

  • O-notare (大湾れ) – Large, sweeping waves.
  • Ko-notare (小湾れ) – Small, subtle waves.

3. Irregular Hamon (Midare, 乱れ)

A highly varied and artistic hamon, featuring random peaks and valleys. It is popular among Bizen-den and Soshu-den swordsmiths.

  • Gunome-midare (互の目乱れ) – A chain-like series of semi-circular waves.
  • Togari-midare (尖り乱れ) – A pointed hamon with sharp peaks.
  • Choji-midare (丁子乱れ) – A clove-shaped pattern, characteristic of Bizen-den.
  • O-midare (大乱れ) – A large irregular wave pattern.

4. Mixed Hamon (Combination of Styles)

Some hamon patterns combine multiple elements, creating intricate and unique designs.

  • Notare-gunome (湾れ互の目) – A mix of wavy and gunome hamon.
  • Choji-gunome (丁子互の目) – A blend of clove shapes and gunome elements.
  • Hitatsura (皆焼) – An extreme pattern where hardening extends up into the blade, creating multiple tempering zones.

5. Special and Rare Hamon

Some hamon patterns are distinctive and less common, requiring great skill to produce.

  • Yakiba-kuzure (焼刃崩れ) – A broken or fragmented hamon that looks rough and uneven.
  • Toramba (虎刃) – A wild, irregular hamon, resembling tiger stripes.
  • Yakiotoshi (焼落とし) – A hamon that fades or disappears near the base of the blade.

Hamon Activities (Hamon no Hataraki, 刃文の働き)

Inside the hamon, various metallurgical formations can appear, adding complexity and beauty to the blade. These are called hataraki (働き, active effects in the steel).

1. Ashi (足, “Legs”)

Thin lines of softer steel extending perpendicular to the hamon.

  • Helps to absorb impact and prevent chipping.

2. Yo (葉, “Leaves”)

Small round temper formations inside the hamon, resembling leaves.

  • Often found in choji-midare hamon.

3. Sunagashi (砂流し, “Sand Drifting”)

Long, flowing streaks inside the hamon, looking like sand being swept by the wind.

  • Indicates high-quality steel grain and skillful tempering.

4. Kinsuji (金筋, “Golden Lines”)

Thin bright silver streaks within the hamon, appearing like lightning bolts.

  • Represents highly refined martensitic formations.

5. Inazuma (稲妻, “Lightning”)

A zig-zagging streak inside the hamon, similar to kinsuji but more erratic.

6. Tobiyaki (飛焼, “Flying Hardened Spots”)

Spots of hardened steel that extend beyond the hamon, creating an artistic effect.

7. Uchinoke (打除け, “Scattered Small Hardened Areas”)

Irregular small round hardened formations appearing inside the hamon.

8. Nie (沸, “Coarse Martensite Crystals”)

Larger, sparkling martensitic crystals that give the hamon a grainy, textured appearance.

9. Nioi (匂, “Fine Martensite Mist”)

A soft, misty transition zone between the hamon and blade body, caused by diffuse martensitic structures.