The Japanese Sword Making Process
|Raw Material Tamahagane (steel) which is produced and refined from iron sand and charcoal in the Tatara furnace are subdivided into lumps relative to their individual carbon concentration.|
|Folding High quality Japanese swords are composed of various distinct sections of different types of steel. The different grades of steels are individually and repeatedly heated, hammered and folded to remove impurities thus improving the strength of the steels. The lower carbon steels which produces a softer metals will be used for the more flexible back and core of the blade. While the highest carbon steel is selected for the blade with slightly softer steels being used for the sides.
Each block is then elongated, cut, folded, and forge welded again. The steel is folded sideways and lengthways to produce the desired grain pattern. This process is repeated from 15 to 20 times creating steels of hundreds of thousands of layers.
|Forming This manufacturing technique uses the different types of steel in specific parts of the sword to accentuate the desired characteristics in the relative areas of the sword beyond the level offered by differential tempering. The vast majority of modern katana are composed of only one or two different steels. Most commonly the hardest ‘tamahagane’ steel is hammered into a bar, bent into a U shape into which the softer ‘shingane’ is inserted. They are then forge welded together and hammered into the basic shape of the sword. By the end of the process, the two pieces of steel are fused together, but retain their differences in hardenability. High quality Japanese swords however are composed of various distinct sections of several different types of steel. There are an infinite number of ways the steel can be assembled, which often vary considerably depending on the swordsmith. The more complex types of construction are typically only found in antique weapons where pieces of hard steel are added to the outside of the blade by assembling the different pieces into a block, forge welding it together and then drawing out the steel into a sword so that the correct steel ends up in the desired place.|
|Hot Forging The cutting edge and are then formed by the swordsmith. The tip of the straight bar is cut off in a triangular shape called the Kissaki-point. It is heated and using a small hammer the Kissaki-point is hammered out in the direction of the arrow.|
|Rough Filing or Sensuki The sword is then rough filed to create a smooth blade face.|
|Clay Coating Having a single edge provides certain advantages; one being that the rest of the sword can be used to reinforce and support the edge. The Japanese style of sword-making takes full advantage of this. When forging is complete, the steel is not quenched in the conventional European fashion. To maximize both the cutting edge and the resilience of the sword spine a technique of differential heat-treatment is used. In this process the sword is painted with layers of clay before heating. Placing a thin layer on the edge of the sword ensures quick cooling to maximize the hardness of the edge. A thicker layer of clay is applied to the rest of the blade, causing slower cooling.
This creates softer, more resilient steel, allowing the blade to absorb shock without breaking. The steel is cools at different rates relative to the thickness of the insulating layer of clay paste. By carefully controlling the thickness of the paste over different parts of the blade, Japanese swordsmiths were able to produce a blade that had a softer body and a hard edge.
|Quenching During the quenching-work, all the doors and windows of the work room are shut to avoid a draft which may adversely cool the sword. After heating the blade in a furnace of between 700 and 800 degrees centigrade, only the charcoal and blade is shining. Today most swordsmith adopt only water as quenching agent because it is considered the best medium in which to attain a vibrant pattern. In the past quenching was often done in oil composites which gave the blade a cloudy pattern.
When quenched, the minimally uninsulated edge hardens and contracts, causing the sword to first bend towards the cutting edge.
However because of the thicker clay insulation along the sword spine, which remains hot and pliable for several seconds longer, the thicker back then contracts much further causing the sword to bend away from the edge. This aids the swordsmith in establishing the exact curvature and strengthening of the blade. This stretching and bending of the blade also result in the creation of the Hamon (hardening pattern) which will be further accentuated during the polishing process.
|Filing Each Japanese sword is filed by its maker to add artistic value. The filing pattern is also important as it can be studied to determine the maker of the sword.|
|Engraving the Hi (Ridge Line) Engraved into many Japanese swords is a shallow line called the ‘Hi’. This line serves to make the sword stronger, lighter and add aesthetic appeal.|
|Engraving the Makers Signature The tang is engraved with the signature of swordsmith but only if he is satisfied that the sword is of a high enough quality to which he wants to put his name.|
|Whetting or Polishing Whetting is done by a specialist selected by the swordsmith. The first whetting of a new sword may take several days and requires many different grades of whet stone. This process will bring out the wave pattern of the Hamon (hardening or tempering line) which greatly adds to the aesthetic beauty of the sword.|
|Making the Handle Grip A wooden handle (often magnolia) is attached to the tang and the grip is composed of sharkskin twilled with cloth.|
|Apply and adjust the Habaki (clasp) This clasp is arranged to fit perfectly between the blade guard metal and the sheath. It was often made of silver or gold.|
|Un-decorated sheath Usually today the Japanese sword is kept in a plain un-decorated sheath. Each sheath is custom made, so it cannot be used for another sword.|
|Liquoring and polishing the sheath This ornamental process requirse the skills of another Japanese expert.|