Japanese Sword Construction and Tamahagane Steel  

Steel is formed by the addition of carbon to raw iron during the smelting process. In Japan the traditional source of iron is from a black alluvial sand found in stream beds called satetsu. The iron sand is smelted in a special type of furnace where carbon is added by the use of charcoal in the heating process, resulting in raw steel known as Tamahagane or sand-steel. In historical blades the skillful manipulation of this steel is acknowledged to have created the legendary qualities of the Japanese sword. Modern Japanese smiths credit this steel with producing the extraordinary aesthetic appearance of the historical samurai blades they seek to recreate. Reputable smiths will not consider using modern steels in newly forged blades (gendaito).

There is a technical basis for attributing the unique functional and aesthetic qualities of the Japanese Samurai sword to the use of Tamahagane. The central fact is that Tamahagane is a non-uniform mixed steel that is never heated to the melting point and therefore retains its inconsistency of character. Further, the irregularities in the steel are maintained throughout the forging and shaping process. It is the combination of different steels of different crystalline structure and hardness characteristics that results in the extraordinary cutting ability, toughness and beauty of the Japanese blade. Although blades of similar cutting capability and resilience can be made with modern steels, this is done so only at the expense of the incredible subtle beauty and handling qualities of the blade, not to mention the less tangible qualities of craftsmanship, historical authenticity and integrity of materials.

Steel gets its hardness and ductility from carbon. The difficulty is that beyond a certain concentration, additional carbon not only ceases to make the steel harder but makes it brittle. Too much carbon and the blade is too easily broken – not enough carbon and the blade cannot hold an edge. A good sword blade requires the contradictory characteristics of flexibility to withstand bending and shock and an extremely hard edge that will maintain its sharpness.

Crystaline Steel

Steel has a unique set of qualities with regard to its crystalline structure. This structure changes and takes on a different form and material properties during the heating and cooling process.  As far back the 1200s now legendary Japanese smiths were able to recognize and take advantage of these apparent physical qualities in the steel. The result was swords  representing the ideal blend of form and function.

Different temperatures achieved during forging result in different crystalline structures of iron and steel. Different crystalline structures create different hardness and flexibility in the steel as well as aesthetic characteristic such as light refraction and color.

When heated in the presence of a carbon source the molecular structure of raw iron opens to allow the entrance of an atom of carbon into the structure. This forms the basic crystalline steel structure that is called austentite.  When cooled suddenly through rapid quenching in water the austentite changes to a tighter crystalline structure called martensite which is much harder. The more carbon that is available during the heating process the more martensite is created during quenching. Up to a point, the more austentite that is converted to martensite the harder the steel - beyond that point the steel ceases to harden and just becomes more brittle.

Importantly, when Austentite is cooled more slowly it reverts back into pure iron and a combination of iron and crystalline steel known as Perlite. Perlite is softer than martensite but much more flexible and shock resistant.  By precise control of the heating and quenching process the smith can craft blades with perlite bodies which are softer, more resilient and tolerant to shock, while maintaining an extremely hard martensite edge with exceptional cutting ability.

Folding- Purification and Aesthetics

Upon smelting, tamahagane looks like a small meteorite and contains numerous impurities and carbon levels. The smith will first break up the steel and treat it at his forge. He will then carefully select the pieces that he wants, shape them into a billet and then hammer and fold it over repeatedly to remove the impurities and create a more uniform carbon content in the steel.

The folding process also results in the various different textures and light refraction that appears as "Hada" or grain pattern in the finishied sword.  Usually a sword is initially constructed from more than one billet, and new steel is being added to the blade during forging to replace the steel and impurities lost from hammering. Because there are slight differences in the carbon content of the steel in each billet and thus the amount of martensite formation during quenching – this eventually results in the diverse patterns called Hada that create the more subtle visual beauty in the blade.

A softer core is often added to increase the resilience of the blade and this can take the form of several internal blade structures off various levels of compleexity. These internal structures are created to enhance the properties of flexibility and toughness already present in the perlite blade body (see discussion of sword structure).

Contrary to popular conception, folding is not done to create strength through lamination. When using modern steels that are already free of impurities and homogenous with regard to carbon content, folding is only done for the historical aesthetic reason of creating the hada pattern in the blade and approximating the astonishing appearance of the authentic tamahagani blade.

The Habuchi  and the Hamon (differential clay tempering)

Perhaps the most distinct feature of the Japanese blade is the temper line or Habuchi that forms as a white reflective line where the hard martensite cutting edge meets the softer perlite body of the blade. The overall pattern this line forms over the blade length is the “Hamon” and appears in a wide variety of forms and patterns depending on the taste and skill of the smith.

The appearance of the hada is the result of the special clay tempering process developed by Japanese smiths. The blade is covered with different thicknesses of a specific clay/water mixture then carefully reheated and quenched.  Where the clay is thin or absent the blade cools extremely quickly and hard martensite is the result. Where the blade cools more slowly due to thicker clay the result is softer more resilient Perlite. The boundary between the two layers is where the hamon forms.

The areas where the martensite particles cross over from below the hamon into the perlite body are loosely referred to as “activity”. The presence of appropriate activity at the hamon boundary is one of the principal ways of determining whether or not the Hamon is real or one that is artificially etched or brushed.

The Zanshin Tamahagane Blade

We are extremely pleased to offer these Tamahagane swords. These blades are of extremely high quality and aesthetic beauty and are completely unique in there authenticity of materials. These blades expand the limits of the Japanese blade smithing art outside of Japan.