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Forging a Kotanto Blade
A charcoal fire is used to heat the steel for shaping with hand hammers. I often use a heavy hammer for rough shaping and a lighter one for the finishing work. The shaping of a blade is divided into a hot and a cold stage, and each stage further divided into two steps. First a specific type of blank (sunobe) is forged, the shape of which will determine the finished dimensions of the blade. Then the blank is forged into the shape of the blade and allowed to cool slowly. The cold shaping begins with the profile and then moves to the bevels.
Forging the Blank (Sunobe)
In this stage, the volume of steel is allocated to each area of the blade and tang. This distribution will largely determine things like distal taper, proportions, and style of the blade, though the sunobe looks very little like its final shape at the end of this step. In traditional swordsmithing, a practiced eye can determine the outcome of a student’s test at the sunobe stage, without even waiting for the forging of the final shape.
Forging to Shape (Hizukuri)
Forging a sunobe into the shape of a blade is a process of working up and down the steel a section at a time, forming the bevels and establishing the geometry of the knife. As the bevels are narrowed, the outward moving steel tends to curve the blade away from the edge, this must be anticipated and compensated for throughout the process. If it is not addressed early on, there will be no way to correct it later. Keeping the temperature as low as possible and forging almost into the black range each heat is one way to help refine the grain structure of the steel. Enough edge material must be left to have a 2mm thick edge after filing and before yaki-ire.
Rough Shaping (Ara-Shiage)
This stage of cold shaping has two distinct steps, the first to outline the profile, and the second to establish the bevels and sides of the tang. Files are used to profile the blade in a blacksmithing leg vise, adjusting and refining each line slowly, removing to check the overall silhouette often. A sen dai (staple vise) and a sen scraper are used for the rough work on the bevels, filing and drawfiling for the final work. The edge should still be up to 2mm thick after all of the rough shaping is finished in order to reduce the risk of warping or cracking during yaki-ire.
Clay Tempering a Kotanto Blade
Once the steel is shaped as much as possible in its softer state, it is coated with a thin layer of clay along the edge and a thicker layer on the body and spine. During the hardening process, the split second difference in cooling time caused by the clay layer creates two different hardness areas in the same piece of steel. The edge cools faster and forms a very hard steel structure called martensite while the body cools slower and forms a very tough steel structure made of ferrite and pearlite. The boundary between these two areas is called hamon and is commonly seen as a frosted wavy line down the length of a polished sword blade.
When the clay is fully dry, a charcoal fire is used to heat the steel slowly and evenly, taking care not to overheat any part of it. First the spine is heated to bring the whole blade to just below temperature, and then it is flipped over to focus heat on the edge. When the entire edge is at the correct temperature, it is plunged into a water bath, edge down, and held until cool (yaki-ire). The hardness is checked with a file and the process repeated if necessary. After hardening, the clay is removed and the steel is heated slightly again to remove some of the internal stresses (yaki-modoshi). Once this process is finished, and if the steel survives, the blade is ready for togi, hand polishing.
Preparing the Clay Mixture
The clay mixture does not need to have secret or exotic ingredients, but there are a few properties that are desirable in the final blend. The basic recipe is approximately a 1:1:1 ratio of regular clay, stone powder (saved from the polishing process), and charcoal powder. The clay provides the stickiness to keep it together and on the blade, the stone prevents shrinking while drying, and the charcoal helps prevent flaking off in the fire due to heat expansion.
The soft water source is snow or rainwater. Each ingredient is ground in small batches between stone and steel or two stones. Grinding and screening the ingredients as finely as possible is important, especially for the slip layer, as the layer can only be as thin as the largest sized particle.
Applying the Clay (Tsuchioki)
The body and spine are coated in a thin layer of clay that will prevent the steel from cooling too quickly in these areas. A uniform thickness is important for even drying, heating, and cooling during various stages of yaki-ire. An almost runny but not watery mixture helps create a thin and even layer (think pancake batter not butter). When this layer is dry a very thin slip layer of clay that is higher in charcoal content is applied to the exposed edge, the charcoal burns out in the fire and the resulting porous clay surface has been found to cool steel faster than if it was bare. The clay slip also helps prevent oxidation and decarburization (loss of carbon at the surface) while in the fire.
This is the moment of truth for the knife, if it survives intensity of the quenching process it will become a live blade. If it succumbs to the stress and cracks it will become a piece of scrap steel again. Yaki-ire requires intense and singular concentration and even the best smiths lose one out of every four or five sword blades to the process. Even though all the work up to this point may be lost, the benefits far outweigh the risks when a good blade has been born.
In order to provide visual consistency for judging color and temperature, yaki-ire is done at night time or with doors closed and lights off. A charcoal fire is built and the water (heated up almost to boiling for modern spring steels) set near the forge. Not heating too quickly or too slowly, the blade is brought up to its critical temperature and committed to the water with a prayer.
Polishing a Kotanto Blade
After the blade is hardened and tempered, the final geometry is created and the surface smoothed and polished with various abrasive stones. In contrast to other methods, stone polished blades have a different surface look and retain their crisp edges and lines. Polishing is broken into three distinct stages, the rough polish occurring before the fittings and scabbard are made, and the foundation polish and final polish once the rest of the knife is complete.
The word togi (研ぎ) does not differentiate between the action of polishing and the action of sharpening, for a Japanese sword the operations are one and the same, an integral process. A combination of Japanese waterstones, both synthetic and natural, are used to remove smaller and smaller amounts of steel and give the knife its final shape and surface. Each stone is progressively finer and is used with a different orientation so that the scratches from the previous stones may be clearly seen. Once they are erased, the next stone can be used, each time refining the geometry and surfaces towards the final goal. Once the rough polish is finished, work on the blade is halted until after the habaki, seppa, tsuka, and saya are created and fitted. This prevents accidental scratches while working on other parts of the knife.
Rough Polish (Kaji-Togi)
At this stage, the large volume of steel left around the edge for the process of yaki-ire must be removed, and the blade and tang are given their final geometry. The edge of the blade is much harder than it was during the rough shaping stage and steel cannot be removed with any metal tools. A combination of natural and artificial waterstones are necessary for this process.
Care is taken to refine each part of the blade geometry and bring the planes into proper alignment and proportion beginning with coarse stones and quicker removal and ending with very fine stones and subtle adjustments. Tagane-ha (chisel edge) is a common technique for first establishing the centre line of the edge. Both sides of the edge are honed away on a 45 degree angle and then the excess material in between the edge and the spine is removed in sections, similar to the method of using a sen to set the pre-quench geometry after forging.
Process of Forging & Shaping a Kotanto Habaki
Once the blade is in rough polish, it is time to create a custom blade collar for it. This important piece of nihonto hardware is made specifically for each blade and is as complex as making a custom fit piece of jewelery. The function of habaki (鎺) are three-fold; the primary purpose is to secure the blade in the wooden scabbard without any pressure on the blade itself, the secondary is to provide a solid shoulder against which to mount the handle and guard, and the tertiary is to provide a stiffened and vibration-dampened flex zone across the transition from tang to blade and decrease the chance of failure at that critical intersection.
A standard habaki is fabricated from two parts; the jacket, which appears to be the entire habaki, and the machigane, a small compound triangular prism shaped wedge that closes the gap where the hamachi bridges the edge and the nakago no hagata of the tang. Most of the habaki is formed by forging, the final adjustments by filing, and the joining of the two parts by soldering or brazing. Once the habaki is fit, the blade is ready for a handle and the accompanying koshirae.
Forging the Blank
A correctly formed tang and blade are necessary prerequisites to making a functional habaki. The widest point of the knife must be at the area where the blade and tang meet on the spine, and a gradual taper in both directions as well as towards the edge ensures proper strength, balance, and the ability to assemble (and disassemble!) the koshirae. One of the main design points when creating habaki is that they should be quite thin at the front, especially near the spine as that is where they will slide as they are sheathed and unsheathed.
Copper is by far the most common material for habaki. With the exception of the initial bar shape, most forging may be done cold in between cycles of annealing to soften the work hardened copper. The final fit is always done cold in order to harden the copper.
Filing & Shaping
Forging in advance can save quite a lot of filing time later, and some judicious filing before folding can save a lot of trouble after the habaki is closed up. While the goal is to get as close as possible to the final shape, it is generally a good idea to leave some extra metal as the bending may not go exactly as planned.
Bending & Fitting
The process of bending may require several cycles of annealing and forging depending on the accuracy of the original shaping. The sides are brought up and cold forged to the shape of the tang, being careful to work well back from the blade when hammering. When everything is fit well, the excess is cut and filed away and a small compound wedge called the machigane is forged and shaped to sit against the bottom of the tang in the gap where the habaki comes together.
Soldering & Finishing
Heated in a charcoal fire, hard silver solder is used to join the machigane to the habaki in such a way that the habaki is slightly too small to slide all the way up to the machi. Hammering the copper after soldering hardens the habaki as it stretches it to its final dimensions.
Carving & Shaping a Kotanto Tsuka
Once the habaki is made, it is time to create a handle for the blade. Because of the tapering shape of the tang, the handle can be designed to be easily removable for cleaning and sharpening the blade. If the handle is to be finished by wrapping with rawhide, leather, or ito (flat silk cord), these must be also planned into the design. This kotanto will have an all wood handle with a samegawa wrapping and no tsuba, so the only additional hardware required is a seppa, a thin metal washer for the habaki to shoulder against.
A tsuka is created in two distinct stages, first the wood is split and the inside carved to receive the tang, and then it is joined back together and the outside is shaped. To increase strength, the tang is placed slightly off centre in the block so that the nakago-ha (bottom edge of the tang) is fully supported by wood rather than resting against the glue joint.
Making the Seppa
The seppa may rest against the tsuba or fuchi, or in this case against the front of the tsuka. The outline of the seppa will determine the profile of the handle so it is very carefully planned in the context of the finished project.
The opening should be large enough that the tang does not actually touch it but small enough that the habaki can cover it. A punch is used to spread some material from the the top and bottom corners and they are adjusted to grip the corners of the nakago mune and the nakago-ha. Seppa are usually fairly simple, but various patinas, filework, hammer textures, or chisel marks can be used to add interesting details.
Carving the Nakago-ana
The core of the handle is traditionally honoki (朴の木, hou wood, Japanese Bigleaf Magnolia, Magnolia Obavata), and my favorite local island stand-in is Nootka Cypress as it is a similar density clear, straight grained wood that carves nicely and provides a comparable cushioning and strength for tsuka and shirasaya.
Creating a tsuka is begun by selecting an appropriate block of wood, sawing or splitting it into halves, and carving out of each half to seat the tang in place. Carving is done with purpose designed chisels called saya-nomi (鞘鑿). The nakago mune should be centered in the block of wood but the nakago-no-ha (bottom edge of the tang) should be fully seated in the omote half of the wood, slightly to one side. The purpose of this is to keep the tang from placing strain on the glue joint, resting it fully against wood. When the fit is just right and the tang sits tightly in place, the two pieces of wood are joined back together with sokui (rice paste glue), and the handle carved and shaped once dry.
Making Sokui (Rice Paste Glue)
Sokui is a simple wood glue made from rice that is traditionally used for joining wood from tsuka to sliding panel shoji. The all natural glue contains nothing but delicious Japanese rice and a little bit of extra water. One of the reasons rice glue was originally chosen for making tsuka is that it is non acidic, does not degrade either the steel or the wood over time, and does not retain moisture. Another is that, while quite strong, it is not stronger than the wood itself. This allows a scabbard or handle to be split open for cleaning or repair without damaging the wood.
A bite or two of cooked rice is placed on a board and worked with a bamboo or wooden wedge to break all the grains into pulp. As the rice is squeezed under the wedge it becomes like sticky dough. Once there are no pieces left, a few drops of water is worked in to bring the glue to the desired consistency. It should not be runny but should be thin enough to spread evenly on the parts to be joined.
Gluing the Core
A thin layer of glue is spread on one or both tsuka parts, depending on the consistency of the glue. The two parts are tightly bound with a cord or leather strap and wedges further increase the pressure. Using a strap rather than clamps provides an even, non-marring pressure even when the block is not yet perfectly square and true.
This small tsuka will have an unusual ki-fuchi, a wooden accent in place of a fuchi. Pacific Yew is a relatively hard and dense wood with a beautiful rich orange colour and natural gloss. In this case, the accent will be attached to the tsuka and have the grain running vertically to add strength and stability, making it functionally more like a true fuchi or tsukaguchi rather than a floating tsuba.
Shaping the Tsuka
Chisels, knives, rasps, and coarse files are used to turn the block of wood into a graceful handle shape and smooth the contours. This would be the final stage for a wooden handle or shirasaya, but this piece will be finished by wrapping over the core with samegawa. Starting from the profile of the seppa, the shape of the handle is carved at the fuchi and then carried back by stages, working from a squared taper to a rounded one. Extra wood is removed to make room for the wrapping to come.
Wrapping the Tsuka
An additional layer of strength, grip, durability, and embellishment is often added to the wooden tsuka using a rawhide wrap and leather or silk cord. Deer rawhide is sometimes used, but most often samegawa (ray skin) is seen under formal wraps or on its own. Rawhide is stiff and strong, and samegawa in particular has a good grip for the hand or for locking in place any cord that wraps over it.
Ordinarily black samegawa would be created by coating over the rawhide with urushi (natural laquer). In this case a tanned and dyed samegawa will be used due to budget constraints. A paper pattern is made to determine as near as possible the shape of the samegawa needed and then a piece is cut slightly oversize and trimmed down bit by bit. Because the leather is black and the wood very light, strips of dyed paper are glued in place under each of the areas where the samegawa will end. Once this is fully dry, the skin is carefully glued in place and bound with leather cord until dry.
Making the Mekugi
The Japanese sword is unique in its handle engineering as well. The tsuka and nakago are shaped and fit together in such a way that the strength of a single bamboo peg holds the whole unit together and so that removal of the peg allows complete disassembly. This allows the blade to be easily removed for cleaning and sharpening and allows for replacement of the mounting without damaging the blade in any way. In addition to being inserted from the omote side, it is important to note that mekugi also have a correct orientation in the mekugi-ana. The part of the mekugi with the most dots is the outside of the bamboo plant and the strongest. It should be rotated towards the back of the handle, where the nakago places the most strain on the peg.
Because this is a tanto, and a small one at that, the peg need not be bamboo as with a sword. Horn, hardwood, and sometimes metal mekugi are found on antique tanto koshirae. In this case the deep red wood is drawing to mind the colour of an urushi laquer finish. The wood is shaved to a rough taper with a chisel and then smoothed with coarse and fine files as it is slowly adjusted to a final fit before being cut to length. Antler tip leaves a glossy burnished surface and the ends are sealed with 100% pure tung oil.
Carving & Shaping a Kotanto Saya
Once the tsuka is made, it is time to create a saya (scabbard) for the blade. The saya should fit snugly on the habaki, with most pressure to the top and bottom, and should hold the blade securely without rattling or jamming. The lines and proportions must be appropriate to the blade and handle and take into account the appearance of the whole unit.
Similar to the process for tsuka, a saya is shaped in two distinct stages, first the wood is split and the inside carved to receive the tang, and then it is joined back together and the outside is carved, planed, and shaped. As with the tsuka, the lower part of the blade is placed slightly off centre in the block so that the edge is fully supported by wood rather than resting against the glue joint.
Carving the Inside
Creating a saya is begun by selecting an appropriate block of wood, sawing or splitting it into halves, and carving out each half to guide the blade smoothly. Carving is done with purpose designed chisels called saya-nomi (鞘鑿). The mune should be centered in the block of wood but the small flat surface for the edge should be fully seated in the omote half of the wood, slightly to one side. The purpose of this is to align the wood with the tsuka and keep the edge from splitting the glue joint if it ever makes contact with the saya. When the fit is just right and the blade sits in place, the two pieces of wood are joined back together with sokui (rice paste glue), and the handle carved and shaped once dry.
Shaping the Saya
The outside work is carried out using chisels, planes, and occasionally coarse files. The block is first squared up and then taken down to the rough dimensions. The shape of the koi-guchi (saya opening) is marked and carved and then the rest of the block is chiseled down to meet it. A plane is used to smooth and true up the surface and final sanding is done with tokusa (horsetail plant, equisetum hyemale, 砥草, “to” as in togi) glued to wooden blocks with sokui (rice paste glue).
Foundation Polish (Shitaji Togi)
Once the fittings and scabbard are complete, the blade is first given the rest of its foundation polish and then the final polish. Depending on the condition of the blade, the last used stone (#300, #500, or #700) may be repeated again to check that there are no new scratches from the workshop and then finer and finer stones are used to complete the finish.
Most of the foundation polish is carried out with natural (or high-quality synthetic) Japanese waterstones which cause the hamon and other steel activity to show up against the body of the blade. A Japanese waterstone forms a slurry like fine clay with suspended particles in it, water (sometimes with a little baking soda to combat rust) is used to control its viscosity and how much stays on the stone during use. A natural stone gives a nice subtle finish with a unique look due to its slight variation of hardness and grit size.
more information on the finished knife here: Sunahama Tanto