Japanese Sword Tamahagane Making Process

Traditional methods of preparing a kind of steel called tamahagane used for the Japanese sword by tatara system and procedure of making the sword are briefly introduced with the discussions from the viewpoint of metallurgy and thermo-mechanical processing. Such traditional methods are also revealed to be consistent with the modern science and technology. The quenching process applied to the final stage of the procedure is focused to explain how the pattern of blade, the deformation and residual stresses are induced by the computer simulation based on the theory of metallo-thermo-mechanics relevant to the coupled fields among temperature, micro structural change and stress/strain.

1. Introduction

The Japanese sword originally used as fighting weapon is now one of typical traditional crafts with artistic characteristics, and so many monographs have been published in English [1-6] as well as in Japanese. The sword is also interesting from the viewpoint of modern science and technology [7-26] since the way of manufacturing the sword is really consistent with the science as is same as other surviving traditional products. Tawara, a professor of Japanese Sword Research Laboratory, the University of Tokyo, accomplished a monumental work in the framework of metallurgy[10]. Tawara measured the distribution of carbon density, precipitation and hardness in the cross section of the swords in relation with the pattern of blade and sori representing the mode of deformation during quenching. Successive works were made by Bain [7], Suzuki[11-12], Tsuwa[13], and others.

Very few works on the sword were made, however, from mechanical engineering aspect. Ishikawa[14-16] discussed the mechanism of cutting objects from theory of cutting and the shape of the sword from dynamics, and stress/deformation analysis after quenching by the finite element method was carried out by Fujiwara and Hanabusa[17-18] and the present authors[19-26].

As is well known, the Japanese sword is normally made of a traditional Japanese steel made of iron sand, called tamahagane[27-31], and manufactured by a special way, especially by folding the steel.In the first and second parts of the paper, the process of preparing the steel and the way of making the sword are briefly introduced.

One of the most attractive and important stage of manufacturing the sword applied to the end of the process before grinding and polishing is quenching, which induces the characteristic deformation pattern of bending called sori, and the formation of blade. The following parts treat some results of computer simulation of interesting bent shape of the sword and pattern of the blade simulated by a developed code 'HEARTS' [32-35].

The code was accomplished based on the theory of metallo-thermo-mechanics[36-39] relevant to describing the fundamental equations considering the coupling effect among microstructural change, temperature and stress/strain, which have been applied to the simulation of heat treatment processes considering phase transformation including quenching of the sword[19-26]. After discussing an paradoxical characteristics on the heat transfer coefficient between heated steel covered by a kind of thermally insulated clay, called yakibatsuchi, and water as the coolant, some results of simulation of a sword in the quenching process are presented.

2. PREPARATION OF TRADITIONAL JAPANESE STEEL

　

Almost all Japanese swords with some exceptions are made of　tamahagane steel, or noble steel, specially prepared by the tatara system by use of iron sand, but not by normal ore as seen in the old painting.

Fig.1 Old painting of tatara system.

Steels distributed in Japan before Meiji renovation in 1868 were produced by this method, while modern system of iron and steel making had been developed in Europe. The amount of yearly production in the time was approximately 10,000 tons being equivalent to that of Great Britain［40］. 

The steel was used not only for swords, but also for guns, cutting tools, nails for construction of old temples and shrines, and other products necessary for ordinary life.Around the period, the tatara system was replaced by the modern western system except for providing the steel to sword smiths.　 

The Iron and Steel Institute of Japan constructed an experimental system of Tatara in ［27-28］in Sugaya, Shimane Prefecture, and accumulated interesting data of steel making technology. 

Due to the lack of the steel for the sword, the Japanese Sword Museum, Nippon Bijutsu Token Hozon Kyokai, started to organize the tatara system in Torigami, Shimane Prefecture, under the cooperation with Hitachi Metals, Ltd. in 1977, and provides the steel of 3-4 tons every year.

Iron sand with 2-5\% content of iron mined from Chugoku Mountains, which includes the best quality of iron sand in Japan, concentrated to the degree of 60\% by magnets system, while the mineral dressing method by gravity classification　in flowing river had been adopted, which is no more popular to prevent water pollution problem. Such enriched iron sand (masa satetsu) contains 8\% of pure iron Fe and iron oxide Fe2O3 with very small amount of impurity such as 0.026% phosphorus P and 0.002% sulfur S being injurious for carbon steels. Chemical compositions are shown in Table 1. Here, alumina Al2O3 is so rare to be beneficial for low temperature refinement to be stated later.

Table 1 An example of chemical composition of iron sand in virgin and enriched states.　

The enriched iron sand is supplied alternatively to the furnace with charcoal by hands. Figure 2 illustrates the cross sectional view of the furnace under operation with some drainage mechanism constructed to three meters under the ground. Only a difference of the system from the classical one in Fig.1 is that electric motors are used for intermittent air blowing instead of manpowered bellows.

Fig.2 Cross sectional view of tatara furnace

Continuous burning is operated for 70h under the direction of a murage, or chief foreman. The temperature in the furnace is around 1200-1500 deg C lower than the melting point of the steel, which follows that the reduction process of the partly molten state is occurred between iron oxide Fe2O3 and silica SiO2 contained in the clay of furnace. During the process, the initial thickness of 200-400mm of the furnace is reduced to 50-100mm. After taking out the slag from the bottom of the furnace followed by destroying the furnace, a block of blister steel called kera in sponge state with dimension of 2.7m in length, 1m in width and 200-300mm in thickness and with 2-2.5ton containing steel of 1.5-1.8ton is obtained (see Fig.3), while necessary amount of iron sand and charcoal are respectively 8 and 13tons. (It is amazing that the block costs hundred thousand dollars, two hundred times much expensive of normal steel!)

Fig.3 Kera, a block of blister steel.

Steel produced on the both side of the block, where the enough deoxidization is completed by air supplied from kirokan (special wooden pipes) is called tamahagane, or noble steel, which is spelled as mother of metal in Japanese character. Other parts of the block with different chemical composition in Table 2 are also used for the sword making.

Table 2. Chemical composition of tamahagane, forged and core steels.

The chemical compositions of the best part of steel are 1.0-1.4% C, 0.02-0.03% P, 0.006% S, and 0.003-0.004% Ti, being very rare of sulfur and phosphorus even compared with industrial carbon steel (see Table 2).

The steel is cooled by cold environment since the operation is carried out in mid-winter followed by shattering, and distributed to about 300 professional and registered sword smiths in Japan.

 

3. MANUFACTURING OF JAPANESE SWORD

The pieces of the steel with different carbon contents are heated in the carburizing or decarburizing environment, termed jigane-oroshi. This process is made in the furnace burnt by charcoal and ash of rice straws with the blowing air sent by fuigo (blowers). Decarbonization occurs in the part closed to the blower, while CO2 gas accelerates the sintering on the upper parts.

The successive process of making a sword is illustrated in Fig.4. The smith makes a flat plate with a handle termed as tekoita, on which the small pieces of broken flat pieces are piled up covered by a special Japanese paper dampened by water containing clay and rice straws to prevent oxidation on the surface of steel by insulating air. It is known that SiO2 in the clay contributes to increase the impurities including in the slag.

Fig.4 Process of manufacturing the Japanese sword.

Forging process is followed to obtain a block, where about ten to fifteen rounds folding called orikaeshi are repeated to get laminated materials with approximately 1,000 (=2**10) to 30,000 (=2**15) layers. The characteristic pattern of the laminated layers depending on the way of smiths is visible on the surface of the sword, some of which are depicted in Fig.5.

Fig.5 Laminated layers by orikaeshi forging.

Such bonding of each layers during orikaesi process is enhanced by the mechanism of so called mechanical alloying, for which so clean surface of the layers are necessary. This is achieved by dispersing impurities such as oxides and so on with sparks by hammering. The weight of the block decreases during the process to approximately 700-100g in the final shape of the sword.

A bar of shingane (core steel) with low carbon content is wrapped by kawagane or hagane (skin steel) with high carbon for which the tamahagane steel is normally used (see the cross sectional views in Fig.4). This process is called tsukurikomi. After rough grinding by the smith himself, the sword is transferred to the final process of yakiire (quenching), which is the main topics of numerical simulation in the following sections.

Before quenching, a kind of clay, yakiba-tsuchi, mixed by charcoal powder and so on is pasted on the surface of the blade to control the heat transfer intensity to be discussed in Sec.6 as presented in Fig.6.

Fig.6 Tsuchioki, pasting a kind of mixed clay on the blade.

Most interesting situation is that the pasted clay is thick on the ridge while thin on the blade part as illustrated in Fig.7 . Finally the quenching operation of the sword heated up to 800-850 degC into water is carried out. (The temperature of heated sword and cooling water depends on the school of smiths and the material property as well as the dimension of the sword.)

Fig.7 Pasted pattern of the thickness of yakiba-tsuchi

During the quenching process, a white hard part with martensite structure is induced near the blade, while other shining part remains pearlite and ferrite structures. The border of the parts is called hamon as seen in Fig.8.

Fig.8 Hamon, shape of border between quenched and unquenched parts.

Here, wavy or zigzag pattern of the hamon is realized by cutting the clay by a spatulas. A computer simulation how the hamon appears and how the stresses are induced will be treated in the following sections.

4. SUMMARY OF MEATALLO-THERMO-MECHANICS

In such cases of quenching of the Japanese sword, and other machine parts in general, incorporated with phase transformation, fields of metallic structure, temperature and stress/deformation are coupled each other as schematically illustrated in the diagram of Fig.9 [36-39].

Fig.9 Coupling effect among metallic structures, temperature and stress/deformation.

Each field is to be described by the coupled fundamental equations of kinetics of phase transformation, heat conduction equation and constitutive equation combined with kinematic relation and equation of motion, which are summarized in separate page (see separate page of

　

 

5. FRAMEWORK OF DEVELOPED CAE SYSTEM ''HEARTS''

　

Brief introduction of the developed CAE system 'HEARTS' is presented in this section to be used for the simulation of the quenching process of the Japanese sword.

　

+++++ 5.1. Finite Element Scheme and Method of Numerical Calculation ++++

　

Finite element scheme is applied to the fundamental equations developed above, and a new version 2.0 of 'HEARTS' [35] approximately with 35,000 steps consisted of 250 subroutines in several levels is coded by FORTRAN 77. For three dimensional problem as well as two dimensional and axisymmetrical problems (plane stress and strain problems including that of generalized plane strain for stress analysis), which were available in the version 1.0. The 2-D and 3-D isoparametric elements with variable-number-nodes are selected from an element library.

　

A skyline scheme and modified or full Newton-Raphson method are employed to solve these nonlinear equations in each time step. In order to treat unsteady heat conduction equation depending on time, a numerical time integration scheme 'step-by-step time integration method' is introduced, while an incremental method is used for deformation and stress analysis.

　

++++++++ 5.2. Architecture of 'HEARTS' ++++++++

　

The heat treatment simulation code ''HEARTS'' is utilized in the CAE circumstance as illustrated in Fig.10 \ref{Architecture}, being combined with the solver, and pre/post processor such as PATRAN, I-DEAS, or other popularly used processors, and the interface. The data necessary for the simulation is generated by the pre-processor, is output in the form of intermediate file. The data in the file is transferred into the data file for control and initial-boundary conditions as well as the file for the element and node data, while the material data file is constructed separately.

Fig. 10 System architecture of CAE system 'HEARTS'

　

The solver of ''HEARTS'' is divided mainly into four parts corresponding to the equations, and they can be connected by the user's requirement what kind of solutions, coupled or uncoupled, to be solved. The output of the numerical results calculated by the solver are transferred into the files for post-treatment, list image and final results. The data for post-treatment is again stored in the intermediate file through the interface to convert into the final data for post-processor, and several kinds of illustration are available by the user's requirement.

　

6. IDENTIFICATION OF HEAT TRANSFER COEFFICIENT

　

Before quenching the sword into water, the yakiba-tsuchi clay is pasted on the surface as shown in Fig.6 to control the cooling condition of the surface of the steel. Since the temperature distribution is to be calculated in the body of the sword, it is necessary to identify the relative heat transfer coefficient on the metal surface as the function of the thickness of the clay.

　

Series of experiments based on Japan Industrial Standard, JIS-K2242, were made to measure the cooling curve of a cylinder made of silver coated by the clay with different thickness. The reason of the usage of a silver is that the material is not undergone any phase transformation during the heating and cooling process. A thermocouple is mounted on the surface as shown in Fig.11. The cylinder is heated up to 800 degC by a reflection type electric furnace, and cooled in the water.

Fig. 11 A silver rod mounting a thermocouple

　

Obtained cooling curves are demonstrated in Fig.12 as the parameter of thickness of the pasted clay[43]. It is so interesting that the curves for thick clay (t=0.7-0.8 and 0.75-0.9mm) show typical mode with moderate cooling rate due to film boiling followed by severe cooling stage by nuclear boiling, the shape of which are similar to the case without the clay. When the thickness is small (t=0.1-0.15 and 0.2-0.3mm), on the other hand, no film boiling stage is observed, which means that the cylinder is cooled severely from the beginning. This is also confirmed by the observation of bubble nucleation by video camera.

Fig. 12 Cooling curves on the surface of a silver rod depending on the thickness of pasted clay.

Inverse calculation is carried out by perturbation method to identify the heat transfer coefficient on the surface of the cylinder. Results are represented in Fig.13. It is paradoxes to be noted from this figure that the coefficient in the case with thin clay gives higher value than without clay during 800-400 degC being most important temperature range for quenching. This data will be employed as the boundary condition when solving the coupled heat conduction equation.

Fig. 13 Temperature dependent heat transfer coefficient.

　

7. SIMULATED RESULTS OF QUENCHING PROCESS

　

7.1. A Sword Treated and the Condition of Simulation

　

The shape and dimension of the sword treated here is illustrated in Fig.14, which is a model of a classical and famous sword termed Bizen-Osafune. 

Fig. 14. Shape and dimension of a sword treated.

Three dimensional finite element mesh division of the sword is represented in Fig.15, where the division is made for a half part in the width direction due to symmetry. Figures 15(a) and (b) respectively denote the whole region and the enlarged part near kissaki(tip).

(a)Global view.

(b)Near the tip.

Fig. 15. Finit element mesh.

　

Total number of the elements is 828, and that of the nodes is 1230. This model is supposed to consist of two regions, (see Fig.16(a)), core steel with 0.2\% carbon content and skin steel with 0.65%C to which different material data are applied. To differentiate the relative heat transfer coefficient depending on the thickness of the yakibatsuchi clay, the surface of the sword is divided into two parts shown in Fig.16(b) with different value indicated in Fig.13.

Fig. 16 Division of the sword for two materials with different carbon content (a) and for two kinds of surface area with different heat transfer coefficient (b).

　

The sword is uniformly heated up to 850 degC, at which temperature the whole region is changed into austenitic structure, and the sword is quenched into the water of 40 degC.

　

7.2. Effect of Pasted Clay on the Formation of Quenched and Unquenched Border

　

To know the effect of the thickness of clay on the induced hamon (border between quenched and unquenched regions), simulation of quenching under several different conditions were carried out. Red parts of Fig.17 show the volume fractions of martensite after quenching for different way of pasted clay. When the sword is quenched by pasting thick clay of 0.8mm, martensite hardly appear except for the part near the blade (see Fig.17(a)), which follows that very thin hamon occurs. However, almost whole region become martensite as seen in Fig.(b) when thin clay with 0.1mm thickness is pasted on the whole surface. If the clay is pasted thin on the blade side, and thick on other part, on the other hand, ideal distribution of martensite is obtained by the simulation with hardened blade by martensite and with ductile main body by pearlite as is so realistic as the normal sword. Hereafter, the simulation below is made with the pasted yakibatsuchi clay of the final pattern.

Fig. 17 Martensite fraction corresponding to hamon, depending on the way of thickness of 

pasted clay.

　

7.3. Variation of Temperature, Metallic Structures, and Associated Deformation

Figure 18 shows the temperature distribution of the sword with successive time from the beginning of the quenching, and the mode of deformation is also depicted in the figure. The part of blade near the edge with thin thickness shrinks due to thermal contraction by severe cooing, which leads to the bending to the downward termed as gyaku-sori or reverse bending at t=1s as is shown in Fig.(b).

Fig.18 Successive deformation associated with temperature distribution.

　

When martensitic transformation starts to occur in that part, however, normal bending called sori to the upper direction is observed due to the volumetric dilatation by martensite formation (see Fig.(c)). Gyaku-sori again appears at t=3-4s, because of the pearlitic transformation in the part of ridge. In the successive stage of cooling, hot ridge side shrinks gradually because of thermal contraction, and finally, the normal bending can be obtained.

　

Thus simulated deformation gives the good agreement with the actual bending mode of sori. Such mode of successive deformation due to martensitic and pearlitic transformation is shown in Fig.19.

Fig. 19 Successive development of structures

　

7.4. Stress Distribution and Residual Stresses

　

Stress distribution in the longitudinal direction in the course of quenching is represented in Fig.20. 

Fig. 20 Longitudinal stress distribution and residual stresses.

The simulated residual stresses after complete cooling are compared with measured data by X-ray diffraction technique on the lines along Hasaki (edge), Shinogi (side ridge) and Mune (ridge)(see Fig.14) as shown in Fig.21.

Fig. 21 Comparison of calculated residual stresses with experimental data.

　

It is also noted that the maximum stress near the top of the sword during quenching reaches the fracture stress, which sometimes leads to cracking or breakage of the sword during the operation.

　

8. CONCLUDING REMARKS

Procedure of preparing the traditional Japanese steel, tamahagane, followed by the method of making the Japanese sword is summarized in the first part of the paper from the scientific point of view. Theory of metallo-thermo-mechanics relevant to the simulation of quenching processes and the brief introduction of the finite element computer code 'HEARTS' are also stated.

　

As an example of the application of the simulation of quenching processes, a Japanese sword is focussed, and the change in temperature, metallic structure and stress/deformation are calculated. The results reveal to represent such real situations. The discussion from the viewpoints of metallurgy and mechanics are carried out in each section of preparing Japanese steel and manufacturing the sword, especially on the effect of pasted clay.

　

In conclusion, the technology surviving for over thousand years is really consistent with the modern science and technology.

　

 

Acknowledgements

　

The author wish to express his hearty acknowledgement to Prof. K. Ishikawa, Kanazawa Institute of Technology, Mr. J. Nozaki, Metal Museum, Mr. T. Suzuki, Nippon Bijutsu Token Hozon Kyokai, for their providing instructive information on the science of Japanese sword. Cooperation to develop the CAE system ''HEARTS'' and identify the heat transfer coefficient are made respectively by Mr. K. Arimoto, CRC Research Institute (now moved to SFTC Co.) and Mr. H. Kanamori and co-workers, Idemitsu Kosan Co., respectively. The numerical calculations by use of the system are carried out by Mr. T. Uehara and Mr. H. Ikuta, graduate students of Kyoto University.
　
 

*********** References ***********

　

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the source of the article: Process of a Japanese Blade

Tamahagane and Types of Steel

Tamahagane and Types of Steel

History
According to tradition, swords originally found inwere forged by foreign travelers such as the Chinese. However, Japanese sword smiths are credited with the refinement of a process that incorporates unique usage of steel compounds and forging techniques to produce the characteristic design of traditional Japanese swords.

Interestingly it is because of the lack of iron ore (or the lower quality of the ore) that Japanese sword smiths developed a technique to remove imperfections contained in the raw steel they used for their swords. Initially blades were constructed from only one type of steel (non-laminated, or maru) but eventually smiths used multiple variations of steel to alienate as many useful properties for the sword as possible. For instance, soft steel was used for the main portion of the blade to provide for flexibility; hard steel for the cutting edge, and medium steel for the sides and top of the blade. The primary type of steel used traditionally was tamahagane, produced by combining lower quality local iron ore with carbon in a specific smelting process.

Modern Swords
In general there are three types of steel that most Japanese swords smiths use today: 420 J2 Stainless Steel, High Carbon Steel, and Folded (Tamahagane) Steel. Please note that folded steel does not actually refer to the elements of the steel, but how it is forged. Stainless steel blades are typically manufactured to be owned as show pieces rather than to be used in battle. High Carbon Steel blades can be used in the dojo due to their strength, although folded steel blades would be more desirable for fighting because of their maximum power and flexibility.

The folding process increases strength and flexibility as the sword smith will work to repeatedly hammer out any impurities from the steel with each repeated fold. That said, older steel (or Tamahagane steel with a carbon content of 1% to 1.5% versus 0.1% to 0.3% of average knife steel) tends to be richer in oxygen than newer steel (or steel with a lower carbon content). This property means that oxidized portions of the metal are extremely soft and pliable so they can be easily stretched and through repeated smelting become finely dispersed and almost unsusceptible to damage. Repeated smelting, folding, and hammering by the smith also produces the intricate blade patterns unique to Japanese swords and also allows for a high sheen when polished.

Stainless Steel
As mentioned above, although beautiful, stainless steel swords are not meant for dojo fighting due to the fact that their molecular structure is simply not as hard or solid as higher levels of steel. This fact does not change depending on where said stainless steel comes from—stainless steel is always stainless steel in terms of chemical makeup. Meaning, it is high in chromium (to enhance the grain and polish) which weakens the internal structure of the blade compared to high carbon steel.

High Carbon Steel
Blades made with high carbon steel are stronger in nature than stainless steel due to their chemical makeup. Sometimes 5160 steel is used in the making of Japanese swords (a compound similar to what is found in truck springs, hence the term, &quote;spring steel&quote; that is sometimes used), or higher end katanas may be forged from welded cable steel, or from the AISI 10xx series (1050, 1084, 1095). Whatever the case, the steel must be clay tempered to create an authentic hamon (temper line) which cannot be formed using high alloy steels (such as stainless steel).

Tamahagane
As mentioned above, Tamahagane steel's high carbon content and forging process make it very desirable for modern sword collectors as it represents a dedication to traditional Japanese smithing methods. Its strength and durability are legendary. Although some modern steels are beginning to gain popularity (such as L6) it is still amazing to note that smiths using a poor quality ore designed a process that created some of the strongest Japanese swords still in existence today.

Conclusion
When purchasing a sword, be aware that the chemical makeup and how the blade was forged will determine its strength and durability. Depending on your budget and reasons for purchasing, make sure to inquire about these issues to ensure you get the sword you desire.

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A Brief History Of The Development Of Khosirae

Koshirae derives from the verb “koshirareru”, which is no longer in use nowadays. Usually “tsukuru” is used instead; both mean “make, create, manufacture”. More accurate is actually “Toso”, which means sword-furniture: “Tosogu” are the parts of the mounting in general, and “Kanagu” stands for those made of metal. “Gaiso” are the “outer” mountings, as opposed to “Toshin”, the “body” of the sword.

Nihonto are classified by length and koshirae and the combination of both. Swords over 2 shaku (1 shaku ” 30.3 cm, or about 1 foot) from tip to munemachi (notch where the tang starts) are daito, from 1 to 2 shaku are shoto, and under 1 shaku are tanto. The usual daito are the katana and tachi; shoto are mostly wakizashi, and there is an infinite variety of tanto. Borderline cases are kodachi (tachi shorter than 2 shaku) and O-wakizashi (wakizashi of *almost* 2 shaku). Women used to carry a tanto in the Edo period in a “brocade bag” in their obi; this tanto for self-defense was called kaiken.
The first swords made of steel were imported from China, and had Chinese mountings. The koshirae prototypes of purely Japanese design developed during the Nara period (646 ~ 794 AD), although they were still called “Kara-tachi”, i.e. Chinese tachi. Only a few survived time, but there seemed to have been two types: swords in black lacquered wooden mountings for actual combat, and those richly decorated with semi-precious stones and fancy lacquering. Rayskin was used on the handles from time to time, but only became common during the Heian period (794 ~ 1185 AD). Swords of that time were called “Kazari-tachi” (decorative tachi) or “Hoso-tachi” (narrow tachi), already adjusting in blade construction to Japanese taste and usage. They were luxuriously mounted, and meant for use by the palace guard at the imperial court. Later on they became a little bit simpler with a “Shitogi-tsuba” (rice cake tsuba), renamed “Efu-tachi”, and were still in use during the Edo period by imperial guards and high ranking officials.

Another interesting sword is the “Kenukigata-tachi” (hairpin tachi), and there is much speculation about its usefulness. Since it has a forged handle, it must have been pretty tiresome to use, although there are some examples with battlemarks. But it is believed that it served mostly decorative purposes, or as presents to shrines to celebrate a happy occasion. Most fighting swords were pretty sombre with mountings in black lacquer or covered with leather (Kawazutsumi-tachi). At the end of the Heian period and the following Kamakura period (1185 ~ 1336 AD), the “Hyogo-Kusari-tachi” was very popular. It was named after the chain-hangers, and usually was covered with metal foil.
The first “Itomaki-no-tachi” were used in the Nambokucho period (1336 ~ 1392 AD). They had tsukamaki as well as sayamaki, i.e. there was wrapping at the upper part of the saya to prevent damage from rubbing against the armor. The itomaki-tachi became the tachi of choice for the following centuries for use in battle. Sometimes the lower part of the saya had a cover made of fur to protect it from the elements, which was called “shirizaya” (butt saya).

Although the “uchigatana” (lit. “strike-sword”) already had its predecessors in the Heian period, it became standard for foot soldiers during the Nambokucho period. Unlike the tachi, which was carried edge down, and had two obitori (hangers) on the saya, the uchigatana is worn through the sash, edge up.
Tachi were still produced during the Muromachi period (1392 ~ 1573 AD), but the uchigatana became the most common daito. Kanagu other than the tsuba, up until now made from yamagane (“mountain metal”, unrefined copper), was often made from shakudo, copper with 5% gold, patinated a deep black. Uchigatana still looked very much like tachi except for the obitori, and therefore were called “handachi”, half-tachi; this style never really went out of fashion during the next 300 years.

Since the early Muromachi period, the manufacture of tsuba became a separate profession; until then, tsuba were forged by swordsmiths, armorsmiths or Kagamishi, mirror smiths (polished disks of metal were used as mirrors). Early tsuba had sukashi, cut-outs in negative silhouette, but from now on brass inlays and positive silhouette sukashi, especially from Owari province, became more refined. The Shoami family became one of the main manufacturers of tsuba, with many generations to follow.
The Momoyama period (1573 ~ 1603 AD) is well known for its flamboyant koshirae with red lacquered saya and kanagu in gold. Those flashy mountings however were counterbalanced by Tensho-Koshirae (era name of emperor Tensho, 1573 ~ 1586 AD) with black saya and “same”, a tapered tsuka with leather binding crossed over a kashira made of horn.
Part of the tsubashi from Kyoto moved to Akasaka in Edo, and produced many fine sukashi tsuba. The Myochin family switched from manufacturing armor to making tsuba. Echizen province tsuba were dominated by the families Akao, Nagasone and Kinai; the Kinai had from their second generation on a special relationship with Echizen Yasutsugu, the Shogun’s favorite smith. They not only carved the dragon horimono for his swords, but also the Aoi-no-Gomon, the family crest of the Tokugawa, on the tang of his swords. Both motifs are also very often found on their tsuba.

In Higo province the tosogushi were encouraged by the Hosokawa Daimyo, and worked in iron, copper, brass and cloisonne. The characteristics of Higo koshirae are the rounded kashira and kojiri; the “same” is often black, and the saya in samenuri – the “valleys” in the “same’ filled with lacquer, and the “mountains” polished flush. Tsuka had often a leather wrapping. This kind of koshirae was later copied as “Edo-Higo-Koshirae”, but mostly with simpler saya and natural colored “same”.
After Tokugawa Ieyasu moved to Edo, many artists set up their workshop there. In the Edo period (1603 ~ 1868 AD) the Goto family, which already had worked for the Ashikaga, almost dominated sword fittings, especially for the daisho. This combination of katana and wakizashi became the standard for samurai during the Momoyama period.
As with many other things, wearing of swords was regulated. For example, in Genna 9 (1624 AD), red saya, swords over 2 shaku and square tsuba were prohibited. Commoners weren’t allowed to wear swords at all.
Samurai at the castle in Edo wore the Banzashi daisho, “duty attire”. “Same” had to be white, the saya black lacquered and with horn fittings. The kojiri of the katana was flat, and that of the wakizashi rounded. The kashira had to be horn, with the black tsukamaki crossed over it (kakemaki). The fuchi and midokoromono (“things of the three places”: menuki, kogai and kozuka) had to be shakudo-nanako (fish-roe pattern) with the only decoration being the family mon (crest). The tsuba was polished shakudo without any decoration. However, this was not always strictly enforced, and kanagu with shishi (lion dogs), dragons or floral motifs were tolerated.

Samurai had to wear the “Kamishimozashi” when on official duty, with the “Kataginu” wing shoulders and “Hakama” split skirt trousers, while Kuge (court nobles), Daimyo and other high ranking officials were clad in the Hitatare court attire with Eboshi-hat, with a wakizashi at their hip. This was either an aikuchi (“meeting mouth”, i.e. without tsuba) or hamidashi (a very small tsuba) in dashizame, or hilt covered in “same” without tsukamaki. This short sword didn’t have a mekugi to fasten the hilt to the tang, which rendered it impractical, because the wearer wanted to show that – due to his high rank – he didn’t have to use it anyhow. Besides, it was a serious offense to draw a sword at court, as anybody who read or watched “Chushingura“, the 47 Ronin, would know.
Bronze, copper and brass were widely used with “regular” swords, as well as the alloy shibuichi (“one quarter”, 75% copper and 25% silver) Those soft metals were called “kinko” (gold/precious metal work) as opposed to iron mountings. Pure silver mountings are quite rare, as are pure gold mountings, which were banned in 1830.

Yokoya Somin left the Goto school, which only worked with shakudo, and invented “katakiribori”, engravings with a triangular chisel. In Nara, the Nara-Sansaku (“three makers from Nara”) (Nara Toshinaga, Sugiura Joi, and Tsuchiya Yasuchika) became famous with sunken relief.
Yagyu tsuba developed from Owari tsuba, so called after the Yagyu family, fencing instructors for the Shogun. Typical Yagyu koshirae has a ribbed saya, and the menuki are at reversed positions of regular menuki placement.
At home samurai put their daisho on a double-rack, edge up, katana on top, tsuka to the left. Actually they were greeted at the entrance of the house by their wives, who carried the swords after pulling the sleeves of their kimono over their hands in order to not touch the swords with their bare skin. They then put a tanto into their sash, which was not subject to any restrictions, and was often lavishly decorated.
Although commoners weren’t allowed to carry any swords, some of them, especially rich merchants, showed off their wealth by sporting expensive tanto, walking a very thin line between status symbol and severe punishment. Physicians wore tanto made of solid wood, and firefighters sometimes had a tanto with a saw instead of a blade.
On July 18, Shoho 2 (1645 AD), the ban of wearing swords was reduced to swords over 1.8 shaku, if one obtained a permit. This enabled travelers on the Tokaido road to arm themselves against robbers which were encountered quite frequently in unpopulated areas, and also enabled the chief of police of Edo to arm the “Okappiki”, non-samurai police.

The end of the Edo period is called “Bakumatsu”, and brought many changes to the samurai class. Some already tried western clothes, and wore “Toppei koshirae” swords, also called zubon (trousers) koshirae, which had no tsukamaki and a softly rounded kojiri. In 1871 everybody was allowed to carry a sword or to wear their hair “Chonmage”, samurai topknot. Kirisute-gomen was prohibited, which was the unpunished slaying of a non-samurai for a (real or imagined) insult. But the Haitorei edict, which took effect on January 1, 1877, limited the right of carrying swords to the military and police. Most swords concealed in a cane or walking stick are made shortly after this edict.
Swords of the Meiji (1868 ~ 1912 AD) and Taisho (1912 ~ 1926 AD) period were fashioned after French and German military sabers, and only the gunto (military swords) after 1933 saw a renaissance of Japanese design.

Koshirae of Special Interest

Nodachi
During the Kamakura and Nambokucho period, tachi of extended length were sometimes used on the battlefield. Those swords certainly had an intimidating effect on the enemy, but their usefulness is highly questionable since they were very awkward to handle. Most were of very low quality.
Chiisagatana
Chiisagatana, lit. “short katana”, are shoto mounted as katana. Now, one could argue that wakizashi are shoto which are mounted in a similar way to katana, and that’s absolutely correct. But we’re talking here about the predecessors of the daisho, the formal katana/wakizashi pair. In the transitional period from tachi to katana, katana were called “uchigatana”, and shoto were referred to as “koshigatana” (hip-sword) and “chiisagatana”, in many cases quite longer than the later “standard” wakizashi.
One can’t make out the difference between wakizashi and chiisagatana by blade alone, although a Koto shoto close to 2 Shaku (like the above mentioned O-wakizashi) would be a good indication; it depends on the mountings. Chiisagatana are the early shoto type with koshirae not easily distinguishable from the uchigatana, just shorter, but in any case with a tsuba (another term for chiisagatana is “tsubagatana”, “sword with tsuba”, as opposed to aikuchi). The ban of carrying swords for non-Samurai wasn’t in effect yet, so people from all runs of life, who preferred shorter blades, would have chosen the chiisagatana/ koshigatana/ O-wakizashi/ tsubagatana.
Daisho
As already mentioned, a daisho (lit. “big/small”) is the katana/wakizashi or katana/tanto pair that was one of the outer attributes of the samurai. Most daisho were mounted en suite, but actually any combination of a short and a long sword is considered a daisho; and it is either a wakizashi or a tanto together with the katana, never both.
Ninjato
Actually, there is no such thing as a special purpose ninja sword, although Hollywood and Toei filmstudios want to make us believe that. But neither ninja nor “Onmitsu Doshin”, the undercover agents of the Edo police, had a “standard” short sword with a straight blade, square tsuba and black fittings.
Present day SWAT teams and military commandos use special or modified weapons to suit their task, and so did assassins and spies of the Edo period. A shorter sword slung over the back might have proven useful for penetrating a castle and combat in confined spaces, but different situations would have called for a different sword. “Ninjato” has a nice ring to it, but the “sword shopping guide for spies” has yet to be discovered …
General Remarks on Koshirae and Placement of Fittings
When restoring an antique sword, or mounting a newly made shinsakuto for the first time, it is often difficult to make a choice in regard to the style and color of the tsukamaki, the saya, and the proper placement of the fittings. Although it’s basically a matter of personal taste, there are a few rules concerning selection and placement of koshirae.
Generally speaking, “up” and “front” of fittings would be as viewed from the side, or the tip of the tsuka, when the sword is held horizontally, sword edge down in case of a tachi and edge up for any other sword/dagger.
Tsuka
There are four basic shapes of tsuka:
1. “Haichi Tsuka”, the most common, the mune-side almost straight, the ha-side slightly tapered, following the lines of the sword
2. “Rikko Tsuka”, almost hour glass shaped
3. “Imogata” (“potatoe shape”), both sides straight
4. “Morozori”, closely following the shape of the saya, mostly with tachi/ handachi
The length of the tsuka was usually tailored to the individual swordsman‘s specifications. As a rule of thumb, the length of the handle of a katana is twice the width of the hand plus two fingers, the wakizashi 1.5 hand widths and the tanto one hand width. Average length of a katana tsuka used to be 8 sun (24 cm or 9.5 inches).
Tsukamaki
It is not historically proven, but traditional Kabuki and Chambarra (period movies) indicate the rank of a samurai by the color of the tsukamaki: black – blue – dark brown – light brown – gray – purple – white. However, since this approximates roughly the percentage of colors found on swords, it might be about right.
The most common wrapping method is “Tsumamimaki“, the ito “pinched“ at the crossing, followed by “Hinerimaki“, where the ito was folded over twice at a 90 degree angle at the crossing. Tachi were usually done in “Hiramaki“, the ito simply crossed over.
Mekugi
The Mekugi is made from seasoned bamboo, convex shaped, and inserted from the side of the tsuka that is covered by the palm. Bamboo is strong yet elastic, and even if the mekugi breaks, the tough fibers will prevent the blade from slipping out of the handle. Sometimes horn or metal was used instead of bamboo, but usually not on swords intended for fighting.
Menuki
Menuki were originally used to cover the mekugi pin that fastens the handle to the tang. Later on they became purely ornamental, and were placed about one hands width from the fuchi on the omote (outward side) and the kashira on the ura (side facing the body) on tachi. However, when the uchigatana was “invented“, the placement wasn‘t changed for traditional reasons, although the sword was now worn edge up and in effect resulted in a reversed position of the menuki.
An additional benefit of the menuki placement of tachi was the better grip on the tsuka, since the menuki filled the gap in the palm of the hand. But “Gyaku-Menuki“, or “anatomically correctly“ placed menuki were almost only used on Yagyu koshirae.
That menuki became more or less decorative elements of the tsuka is evident on tanto (and to a lesser degree on wakizashi). On the short handle of a tanto they were almost opposite of each other, and sometimes even omitted.
Tsuba
Sometimes it might be difficult to determine the front (i.e. facing away from the body) and back side of a tsuba. If the tsuba has a kozuka hitsu or kogai hitsu (slots for kozuka and kogai), the one for the kozuka is always to the left and the one for the kogai always to the right. The mei (inscription) of the maker is usually on the front, but there are sometimes exceptions. In most cases the more decorated side is the front side. If it is an undecorated tsuba, or a sukashi tsuba, without any slots, the side showing more wear is probably the front.
The average diameter of a katana tsuba, measured at the widest part, seldom exceeds about 7.5 cm or 3 inches.

by C. U. Guido Schiller

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