What Is Hamon on a Japanese Sword？

Hamon (刃纹) – The Soul Line of a Japanese Sword

The hamon, also known as the temper line, is one of the most important and beautiful features of a Japanese katana. It is created through a complex process of folding, forging, clay coating, and quenching.

Before quenching, the sword is covered with a special layer of clay. The edge of the blade is left exposed, while the spine is covered with thicker clay. When the hot blade is placed into water, the exposed edge cools down very quickly and becomes extremely hard, while the clay-covered spine cools more slowly and remains more flexible.

The visible boundary between these two different hardness zones is what we call the hamon.

The Beauty Created by Fire, Water, and Steel

Quenching is the final and most dramatic battle between fire, water, and steel. Because the blade is made from layered steel and covered with clay of different thickness, the sudden temperature change during quenching creates countless natural patterns.

Near the hamon—and sometimes even far from it—you may see lines that look like gold threads, silver streaks, lightning flashes, or glowing sparks. You may also notice small crystal-like grains, created by the steel’s internal structure.

Some of these patterns come from folding and hammering, and when viewed closely, they can resemble traditional Chinese landscape paintings—mountains, rivers, clouds, and flowing mist. This beauty is not just on the surface. Even if the blade is polished again, the pattern remains inside the steel. It is a natural beauty that cannot be erased.

From a scientific point of view, the hamon is visible because different temperatures during quenching create different crystal structures in the steel, forming a clear and permanent boundary line.

Types of Hamon

Hamon comes in many different shapes and styles.

In the earliest swords, many blades were repaired due to damage or breakage, and their hamon appeared as a straight line (Suguha), similar to early Chinese blades. Later, swordsmiths developed wavy hamon, and over time, the shapes became more complex and artistic.

Common hamon styles include:

Gunome (互目) – rounded wave shapes
Choji (丁子) – clove-flower shapes with extended “legs”
Sanbon-sugi (三本杉) – triple peak patterns
Midare (乱刃) – irregular and dramatic waves
Tōran (涛乱) – large rolling wave patterns
Hitatsura (皆烧) – full temper across most of the blade

Some hamon look like pine tree bark, some like flowing water, some like wood growth rings, and others resemble clouds, mountains, morning dew, sunset light, or ocean waves. Each sword has its own unique character.

Midare, Gunome, and Choji – The Core Styles

Any hamon with frequent rises and falls is called Midare (乱刃).
When the sword is placed with the spine facing up and the edge facing down, the peaks of the hamon are called “Yaki-atama” (burning heads).

Among all Midare styles, the two most fundamental types are:

Gunome (互目) – rounded arch-shaped peaks
Choji (丁子) – similar to Gunome, but with small “legs” extending toward the edge, making the pattern look like clove flower petals

From a performance standpoint, Gunome is often more practical, while Choji is mainly valued for its artistic beauty.

Hamon and Sword Schools

In ancient times, most swordsmiths specialized in only one or two types of hamon, and different schools and regions could be identified by their hamon style.

Modern swordsmiths, however, usually have the ability to create many different hamon designs based on customer request, so clear school characteristics are less obvious today.

Boshi (帽子) – The Hamon in the Tip

The part of the hamon that appears in the tip of the blade (Kissaki) is called the Boshi, also known as the “cap.”

The shape and quality of the Boshi reveal the skill level of the swordsmith, and it plays a major role in judging the value and authenticity of a Japanese sword.

If a Japanese sword has no visible Boshi, it usually means: