Katana

Making of a Japanese Sword 日本刀

Making of a Japanese Sword 日本刀

Swordsmith
Forging
Working the Ore
Controlling Carbon Content
Fusing the steel
Multiple Firings
Hammering to draw out flaws
Welded back upon itself (folding)
Hammer & Fire about 13 times
Hammering into a Rod
Cooled, Weighed, & Inspected for Flaws
Shaping the Sword and the Tip
Filing the blade into Rough Form
Grinding Stone
Tempering with Clay
Charcoal Preparation
Final Tempering at Midnight (viewing the blade in complete darkness)
Remove Clay
Inspection
Back Flattened
Filing & Filing Patterns
Polishing & Special Polishing
Chisel name & province on metal under the handle

The legitimate Japanese sword is made from Japanese steel “Tamahagane”. The most common lamination method the Japanese sword blade is formed from is a combination of two different steels: a harder outer jacket of steel wrapped around a softer inner core of steel.[40] This creates a blade which has a hard, razor sharp cutting edge with the ability to absorb shock in a way which reduces the possibility of the blade breaking when used in combat. The hadagane, for the outer skin of the blade, is produced by heating a block of raw steel, which is then hammered out into a bar, and the flexible back portion. This is then cooled and broken up into smaller blocks which are checked for further impurities and then reassembled and reforged. During this process the billet of steel is heated and hammered, split and folded back upon itself many times and re-welded to create a complex structure of many thousands of layers. Each different steel is folded differently, in order to provide the necessary strength and flexibility to the different steels.[41][42][43] The precise way in which the steel is folded, hammered and re-welded determines the distinctive grain pattern of the blade, the jihada, (also called jigane when referring to the actual surface of the steel blade) a feature which is indicative of the period, place of manufacture and actual maker of the blade. The practice of folding also ensures a somewhat more homogeneous product, with the carbon in the steel being evenly distributed and the steel having no voids that could lead to fractures and failure of the blade in combat.

Cross sections of Japanese sword blades showing lamination types.
The shingane (for the inner core of the blade) is of a relatively softer steel with a lower carbon content than the hadagane. For this, the block is again hammered, folded and welded in a similar fashion to the hadagane, but with fewer folds. At this point, the hadagane block is once again heated, hammered out and folded into a ‘U’ shape, into which the shingane is inserted to a point just short of the tip. The new composite steel billet is then heated and hammered out ensuring that no air or dirt is trapped between the two layers of steel. The bar increases in length during this process until it approximates the final size and shape of the finished sword blade. A triangular section is cut off from the tip of the bar and shaped to create what will be the kissaki. At this point in the process, the blank for the blade is of rectangular section. This rough shape is referred to as a sunobe.
The sunobe is again heated, section by section and hammered to create a shape which has many of the recognisable characteristics of the finished blade. These are a thick back (mune), a thinner edge (ha), a curved tip (kissaki), notches on the edge (hamachi) and back (munemachi) which separate the blade from the tang (nakago). Details such as the ridge line (shinogi) another distinctive characteristic of the Japanese sword, are added at this stage of the process. The smith’s skill at this point comes into play as the hammering process causes the blade to naturally curve in an erratic way, the thicker back tending to curve towards the thinner edge, and he must skillfully control the shape to give it the required upward curvature. The sunobe is finished by a process of filing and scraping which leaves all the physical characteristics and shapes of the blade recognizable. The surface of the blade is left in a relatively rough state, ready for the hardening processes. The sunobe is then covered all over with a clay mixture which is applied more thickly along the back and sides of the blade than along the edge. The blade is left to dry while the smith prepares the forge for the final heat treatment of the blade, the yaki-ire, the hardening of the cutting edge.
This process takes place in a darkened smithy, traditionally at night, in order that the smith can judge by eye the color and therefore the temperature of the sword as it is repeatedly passed through the glowing charcoal. When the time is deemed right (traditionally the blade should be the color of the moon in February and August which are the two months that appear most commonly on dated inscriptions on the tang), the blade is plunged edge down and point forward into a tank of water.

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