“The Sword and the Chrysanthemum” by Paul Martin Part5: The Production of a Japanese Sword
Text by Paul Martin
Paul Martin and his Kamon(Photo/Steve Morin)
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(Publication period: March 13, 2026 – Aprril 13, 2026)
Following on from the previous chapter on various materials used in the manufacture of Japanese swords, we now continue on with the manufacture of the blade. The methods employed vary somewhat between particular schools and smiths. Therefore, this is a general guide to the most common method of manufacture. This explanation describes the different processes that take place from the raw materials to the completed blade. You will see that the blade is made from a laminated construction of two (or more) different hardness steels. A softer core is inserted into a harder outer steel jacket, before the blade is then heated and quenched to produce a nard cutting edge. The purpose of the softer inner core is to give support to the harder parts of the blade, allowing it to flex on impact, so that it does not break.
It is not uncommon for smiths to make two or three blades at the same time, to ensure one successful blade to fulfil a customer’s order. Various smiths have different opinions, and may use slightly different raw materials, but on average a smith will use about 5 Kgs of tamahagane to produce a single blade. An averaged sized completed katana (tachi are typically slightly longer) by today’s standards has a cutting-edge length of between 70-75 cm.
When thinking about Japanese sword production, it is easy to only focus on the swordsmith. However, even a blade that comes with a plain magnolia (honoki) wooden sleeping scabbard called a shirasaya, requires the skills of at least five craftsmen; the craftsmen that make the raw materials, the swordsmith, the securing collar (habaki) maker, the professional polisher, and the scabbard (saya) maker. A full set of mountings (koshirae) made for use, and therefore wearing the blade require further specialist craftsmen. However, these topics will be covered in more detail in another chapter.
Japanese Sword Blade Production
Kowari (breaking into small pieces)
First, the swordmith will take fist sized chunks of tamahagane, heat them and then hammer them into flat plates. The flat plates are then quenched in water and broken into small even sized pieces of about 2 cm diameter. This is a selection process. The pieces that break cleanly contain a higher amount of carbon and are put in one pile to be used for the jacket steel (kawagane), or the skin of the blade. The pieces that only bend or tear are put into a separate pile as they have a lower amount of carbon and will be used for the core steel (shingane).
Tsumi-wakashi (stacking and heating)
Pieces with a similar amount of higher carbon content are neatly stacked onto a small tamahagane plate attached to a handle called a tekogane that is used to place the billet into the middle of the swordsmith’s fire. The stack is wrapped in paper, secured and covered in a clay slurry. It is then carefully put into the swordsmith’s fire pit, and heated to around 1300 degrees C. Once the billet reaches the correct temperature it is removed from the fire, placed on the anvil and hammered, fusing all of the pieces together into a single block. This process is repeated for the other billet with lower carbon content.
Orikaeshi-tanren (fold-forging)
Next, the billet is the returned to the fire and removed periodically to be stretched by hammering. Once the billet is an optimum length, an incision is made, and it is folded in half. This process is usually repeated between 12 to 15 times for the kawagane, and 6 to 8 times for the shingane (depending on smith or school). This folding process does not homogenize the steel, but does give it more consistency compared to tamahagane in its raw form. The number of layers double with each fold. For example: if it is folded 10 times, one-fold equals two-layers, two-folds equals four-layers and so on. Ten folds equals 2048 layers, 15 folds equals 65,536 layers. Some smiths with fold in alternate directions: First fold is lengthwise, then the second fold is crosswise and so forth. This kind of fold forging is called Juji-kitae. Some smiths also split the fold-forging into two process: foundation forging and finish forging.
Tsukurikomi (construction type)—Kobuse
The completed billet of higher carbon kawagane is now taken and formed into a U-shape. The completed billet of lower carbon shingane is taken and fashioned to fit snugly inside the U-shaped higher carbon steel. This is going to be the softer core which acts as a shock-absorber by giving the blade a degree of flexibility. This style of sword manufacture is called kobuse, and currently is one of the most popular styles of sword construction. The two types of steel are then welded together by hammering. There are other styles of construction that are carried out involving the placement of steel of varying degrees of carbon at specific points before being hammered out into a sunobe. For example, with hon-sanmai the back of the blade would have a piece of steel with the lowest amount of carbon, the cutting edge would have a piece of steel with the highest amount of carbon, whilst the sides would have an amount somewhere between the two. Other construction types include shiho-zume (four different hardness’s of steel around a softer core), makuri (a plate of lower carbon steel placed on an equal sized plate of higher carbon steel and folded in half) and muku (mono-steel).
Sunobe (forming the sword blank)
The kobuse is taken returned to the fire pit, heated and hammered repeatedly until it is stretched out into a long straight bar in accordance with the desired length of the blade. This can be considered a blade blank from which most types of Japanese blade could be produced.
Hi-zukuri (hammering out the shape of the blade)
The sunobe is heated and hammered repeatedly a section at a time until the swordsmith forms the desired shape of the blade. The curvature (sori), ridgeline (shinogi) that runs the length of the blade, the cutting edge and the point section are all produced in this process. The point section is created by first cutting of the end of the blade at 45-degree angle in the reverse direction of the intended shape of the kissaki. The furthest point is then hammered and shaped up towards the back of the blade. The reason for this process is to ensure that core steel is sealed inside the jacket steel within the point section, as it some may have squeezed out from the front of the jacket steel during sunobe production. The blade is then taken for finer shaping which consists of much filing and the surfaces planed using a drawknife type tool called a sen.
Tsuchioki (clay application)
The blade is then covered in clay in preparation for a differential hardening process called yaki-ire (quenching). A thicker layer of clay is applied to the back of the blade, while the cutting edge is coated with a thinner layer. The thinner clay coated cutting edge cools at a much faster rate than the thicker layer covered back of the blade. The rapid cooling causes the crystalline structure of the steel to be much harder at the cutting edge, as opposed to the more slowly cooled back of the blade which allows it to retain its more ductile qualities. The way in which the clay is applied determines the pattern of the hamon. Additionally, thin lines of clay applied perpendicularly across the blade the cutting-edge help to shape the final pattern of the hamon (pattern of the hardened edge) while also serving a functional purpose. Where the lines pass through the hamon to the cutting edge creates activities within the hardened area called hataraki that include yo (lit. leaves), and ashi (lit. legs). Ashi are very small lines extending from the line of the hamon towards the cutting edge. In the case of yo, they appear like falling leaves from a tree. These are in actuality very small slightly softer patches of steel within the very hard cutting edge. When the sword is used, should a chip occur in the edge it may stop at one of these softer places, rather than becoming a crack that transverses the blade entirely. Depending on raw materials, manufacturing methods and quenching, a host of various crystalline activities can appear within the hardened area along the cutting-edge.
Yaki-ire (quenching process)
The clay-covered blade is then left to dry. The swordsmith refills the hearth using a finer grade of charcoal for the quenching process. Once the fire reaches the optimum temperature, the blade is passed through the fire pit repeatedly. This where the skill and intuition of the smith really comes into play. He works the Japanese bellows (fuigo) that are constructed in such a way that it continuously pushes out a stream of air into the fire even whether the smith is pulling or pushing the plunger. This allows him to control the temperature of the fire with his left hand whilst passing the blade through the fire with his right. In order to create a successful consistent hamon along the entire length of the blade, he must heat the entire blade evenly. The smith judges the temperature of the blade by observing the shade of red of the hot blade. If it becomes overheated it will end in a poor result and conversely if it is not heated enough will also end in failure. At the crucial moment, the blade is pulled from the fire, paused for a second over the water trough to align it and to wait for the exact moment to quench it. Additionally, the stresses in the steel brought about by the extreme change of temperature of the quench could also cause a catastrophic failure. Hairline cracks called hagire can occur, rendering the blade (and all the other previous processes) useless.
When the blade is plunged into the water the effect of the sudden cooling of the thinner clay applied cutting-edge initially sends the blade into a reverse curve. However, as the thicker clay covered back of the blade gradually cools, the blade is pulled back into its typical curved shape. Once it is cooled sufficiently the swordsmith takes the blade from the trough and puts it to a whetstone to remove the clay and check the blade is intact and that a hamon was successfully produced. Any warping that has occurred due to the stress of the quench will need adjusting, and the blade curvature to will be tailored to the smith’s desired shape.
Kajitogi (rough polish by the smith)
Using rather rough whetstones, the smith hones the blade to the final shape that he wants it to be. It is at this stage that any carvings such as bo-hi (fuller), or other decorative carvings are incised. Once these are successfully completed, it is then passed to a professional sword polisher. The sword polisher uses various grades of stones and copious amounts of water to bring out the intrinsic beauty of the blade. This allows the viewer to see right into the steel by exposing the crystalline structure. As the process of sword polishing is done completely be hand and requires many different grades of stones. This begins with coarse stones to refine the shape of the blade. The gradually become finer and finer creating a highly polished surface. In between foundation and finishing stages of polishing the blade will also be sent to the habaki maker, and the scabbard maker. This is in case the blade is subject to any scuffs or scratches while being subjected to these processes. It is easier to repair at this stage rather than having to repair a completed polish.
Mei-kiri (inscription incision)
After it has been professionally polished the smith generally inscribes the tang with his name and date of manufacture using a small chisel and a hammer. However, inscriptions can include other information such as the location of production, or if special materials were used, or personal inscriptions requested by the customer.
