Hamon

Through repeated mixing, folding, and forging, before quenching, a layer of clay is applied to the blade, leaving only the edge exposed. This allows the edge to directly contact the water during quenching, resulting in rapid cooling and high hardness, while the back of the blade is insulated by the clay, resulting in slower cooling and lower hardness. The boundary between these two areas is what we refer to as the hamon.

This is an unprocessed katana hamon photo I took with iPhone13 pro max. The junction between black and white is the hamon.

Quenching is the key to the final bet between iron, water, and fire.Due to the combination of different materials and the varying thickness of applied clay, the intense temperature fluctuations in the water create numerous texture variations in the blade. Near the hamon area and even farther, there are peculiar lines resembling gold, silver, lightning, and flashes, as well as crystal grains, varying in size. Additionally, there are traces left behind from the folding and forging process, which, upon closer inspection, bear a striking resemblance to traditional Chinese landscape paintings. However, these patterns are naturally created through the quenching process and possess an inherent beauty. This beauty is not confined to the surface alone; even if the surface is polished away, it remains intact within. Its artistic effect is indelible.

From a scientific perspective, the visible boundary on the quenched blade is the result of varying metal crystal structures caused by differences in temperature.

The hamon comes in various shapes. In the early days, the hamon was straight, similar to Chinese swords. Later, it evolved into a wavy form, and as it further developed, it became more intricate, branching into various styles such as choji, gunome, sambonsugi, midare, hitatsura, and more. Some resemble pine bark patterns, while others resemble swirling water vortexes. Some even resemble wood grain patterns, while others evoke the imagery of floating clouds, towering mountains, morning dew, evening glow, or seafoam. The variations are manifold, each with its own unique charm.

Frequently undulating hamon patterns can be referred to as 'midareba', and if the back of the blade is facing upward while the blade is facing downward, the 'crest' of the hamon is called 'yaki-atama.' Within the midareba category, there are two primary types: 'gunome' and 'choji'. The difference lies in the shape of their crests. Gunome has rounded arch-shaped crests, while choji extends 'ashi（leg）' in the direction of the edge on top of a curving pattern, creating a 'petal-like' effect. Gunome serves a functional purpose in the blade's performance, while choji primarily enhances the artistic appearance of the sword.

In ancient times, many swordsmiths specialized in one or two types of hamon patterns, and one could identify their school or style based on these patterns. In contrast, modern swordsmiths can typically create various hamon patterns as required, making the distinctive school characteristics less prominent.

The hamon on the kissaki is called 'bōshi', and it can also be referred to as 'saki'. The shape of the bōshi can provide insights into the skill level of the swordsmith and, in turn, help assess the value of the sword itself. Japanese swords without a well-defined bōshi are often considered either poorly crafted or have undergone significant repair, potentially due to breakage and subsequent reshaping. Without a proper bōshi, the hardness of the Kissaki becomes unreliable, significantly impacting its value.


Note

kissaki：fan-shaped point of the blade; separated from the body of the sword by the yokote.