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japanese swords

Japanse Sword making Process

Friday, 29 July 2016
This webpage shows the swords making process 

1. Raw material: In ancient times, the resource of the Japanese swords was mainly steel scraps (such as nail, broken pot, plow, etc.) as well as a tamahagane which was refined from the tatara, the traditional iron smelter. Currently, the NBTHK supplies tamahagane to swordssmiths in Japan.

2. Sumi-wari: Splitting wood charcoal is the first step for swordsmaking, which is called "sumiwari". The best charcoal comes from the pine tree but chestnut tree is also used. To make one swords, about 12 - 15 kg of charcoal is consumed. The different size of charcoals control the forging temperature in the hearth and they provide the carbon into the steel. About 2 - 3 cm of even size is used at Kitae (forging) process but smaller size of 1 - 1.5 cm is used in Yakiire (tempering/quenching) process. This sumiwari process is a very important step for smith trainee (There was an old saying that the trainee had to spend 3 years just to learn sumi-wari). Akihira was well known for spending most of his valueable time in the sumiwari so that he couldn't make more than two swordss per month. In order to learn his craftmanship afterward, thesedays no more than two swordss/month is allowed to produce by a smith in Japan.

3. Aku-zukuri: "Aku" means burnt straw which is used in forging process. Aku is used broadly in forging steps e.g. the fixation of tamahagane on takogane in tsumi-wakashi process.

4. Tsumi-wakashi I: Pieces of tamahagane is heated in the hearth to be classified. Based on the carbon content in each piece of tamahagane, they were used for kawagane (skin steel: brittle, hard, high carbon content) or shingane (core steel: ductile, soft, low carbon content). At first, kawagane pieces is stacked on the takogane (flat steel scoop), which also becomes the part of the nakago. Tsumi-wakashi means stacking process.

5. Tsumi-wakashi II: After stacking tamahagane pieces, wetted Chinese drawing paper covers them to fix the stacked pieces. In addition, clay water is slightly poured on it to stabilize them.

6. Tsumi-wakashi III: Aku covers the stacked tamahagane again follwed by another pouring of clay water. Chinse drawing paper, clay water, and aku play important roles on maintaining the uniform temperature of tamahagane in the hearth, preventing the contamination by outer impurities, and stabilizing the carbon content inside tamahagane.
7. Shita-kitae I: After tsumi-wakashi process, the forging begins. By increasing the temperature of the hearth, stacked tamahagane is heated. This is the beginning of Shita-kitae (Base forging).
8. Shita-kitae II: Hammering onto the tamahagane begins. There is many sizes of hammers used such as o-zuchi (big hammer) which weighs about 1.1 kg. Hammering is another important step for smith trainee. Hammer should be hit the exact position at the anvil. The swordssmith leads the hammering process with his ko-zuchi (small hammer). During this stage, many vacancies inside the tamahagane is revealed to the surface and removed.  
9. Orikaeshi Tanren I: "Orikaeshi" means folding. Forged tamahagane is folded transversely and  longitudinally. At each folding stage, tamahagane is heated and cooled down by water again and again. This procedure oxidize the steel surface and removing these oxidated layers greatly reduce the content of impurities inside steel.
10. Orikaeshi Tanren II: These show the transverse folding.
11. Orikaeshi Tanren III: These show the longitudinal folding. The difference between these two folding procedures lies on that the small hammer is used to fold in transverse folding while the big hammer is used in longitudinal folding. Generally, about 12-15 folings is repeated.
12. Age-kitae (Hada-kumi) I: After shige-kitae which produce kawagane and shingane respectively, another forging step can be added (Age-kitae). Tamahagane is forged again as a shape of stick once more and cut uniformly about 7.5cm long. This age-kitae is an optional step and sometimes omitted. A tight microstrucutre and hada (grain pattern) can be expected after this step and the uniformity of the carbon content is improved.  
13. Age-kitae (Hada-kumi) II: Tamahagane pieces is stacked in cross manner.
14. Age-kitae (Hada-kumi) III: Likewise the shita-kitae, tamahagane is heated and folded 7 to 8 times.
15. Kumi-awase (Honsanmai style): Kawagane, shingane, and hagane is combined each other to designate the swords structure. These photos show the Honsanmai style (Two kawagane, L-shape hagane and shingane connected to takogane).
16. Sunobe-hizukuri: After combining each different tamahagane, long stick of sunobe is  shaped. This forging step is called "Hizukuri". By the direction of the smith with the help of big and small hammers, sunobe becomes the shape of the swords. With a small hammer, the smith shapes, elaborates, and predicts the dimension of the swords in his mind.
17. Kissaki-hizukuri: Kissaki is shaped at the end of the sunobe. When the kissaki is shaped, the shingane should not be exposed and the kawagane should not be thick.
18. Nakago-hizukuri: Nakago is made.
19. Shiage: Mune and hiraji is shaped by chisels. Hamachi and munemachi is also shaped in this step. Finally, the dimension of the swords (sugata) is completed.
20. Yakiba-tsuchi: This is the clay coating to make a hamon. Yakiba-tsuchi is a clay mixture which is high temperature resistant. At first, sunobe is cleaned to eliminate any oil or impurities on the surface followed by the coating of Yakiba-tsuchi. The composition of Yakiba-tsuchi is a top secret to the smith. In general, it's known as a mixture of clay, (polishing) stone powder, and charcoal powder. Clay becomes hardended during Yakiire step and sticks to the steel surface firmly. The thickness of the clay coating determines the cooling rate in quenching. Stone powder is bigger than clay so that it minimizes the the compressive stress of clay during drying. On the other hand, the charcoal powder is burned out in the hearth before quenching and produce a micro-void inside the clay coating. These numerous micro-voids produce micro-bubbles by vaporization during quenching and increase the cooling rate.
21. Tsuchi-oki: The thinner coating of Yakiba-tsuchi is applied to hiraji and the shingiji is coated in  thick manner. These coating thicknesses result in the different cooling rate and consequent microstructure of the steel. Yakiire has two styles: Bizen style in low temperature tempering and Soshu style in high temperature tempering. Different styles determine even the different kind of clay coatings.
22. Tsuchi-tori I: There is two kinds of tsuchi-tori exist. In both coatings, basic thin coating is applied at first. Positive method leaves the thicker clay in hamon isa by recoating the clay with "brush". On the other hand, negative method makes the thinner clay by eliminating the basic clay coating with "scoop". Left photo shows the positive method to make a suguha hamon while the right shows the negative method for a gunome hamon.
23. Tsuchi-tori II: Another photos to show various styles. The left produces choji midis with negative method and the right produces a gunome. Postive method is easier than negative but hamon is not so dynamic. Negative method is difficult to success but the taste of hamon is deep and aesthetic. Akihira usually used the negative hamon coating method.
24. Boshi tsuchi-tori: Boshi is being made in kissaki is boshi. Boshi is one of the main characteristics in the  swords appraisal.
25. Yakiire I: The most important stage in swordsmaking can be the Yakiire (heating-quenching) process. After coating clays onto the blade, it is heated up to 720 - 780C. Smaller wood charcoals is used not to peel off the clay coating. If the process temperature is increased slowly, Nioi-deki of Bizen style can be made. Fast increase of hearth temperature is necessary for Nie-deki of Soshu style. The latter is more difficult than the former.
26. Yakiire II: Once the swords attains the right temperature, it is quenched into the water box (Mizubune). The water temperature is another important factor as well as the speed of quenching. In this stage, the cutting edge bends more because of the martensite transformation of steel which results in 4.4% volume increase. If this volume increase and applied tension stress in cutting edge is not tolerable, the crack (hagire) can be initiated at the cutting edge and propagated.
27. Yakiire III: There is several factors which determine the success of yakiire. They is mainly a clay coating thickness and its composition, quenching temperature and cooling rate, and a swords dimension to endure the tensile stress at the cutting edge. To relieve the residual tensile stress in cutting edge, another tempering (Aitori) is applied sometimes.
28. Sori-naoshi: As mentioned before, the curvature of the swords increases and the smith corrects this curvature if needed cisfully.
29. Kaji-togi: Before tossing the blade to the togishi (polisher), the smith performs a basic togi. Any defects or problems is examined by smith. It was said that the polishing skill of Akihira was much better than usual togishi.
30. Nakago-shitate: Nakago is a face of the smith in the swords. File mark left by chisels in nakago is called yasurime.
31. Mekugi-ana drilling: If the only one machine is used in Japanese swordsmaking thesedays, it's the drill to make a mekugi-ana. In ancient times, it was punched. The poisition of mekugi-ana is usually 7-8cm below from the hamachi.
32. Mei-kiri: The last step is to sign the name of smith on the nakago. Sometiems, the swordssmith signed in different way according to the quality of the swords he made. The above shows a Tachi mei.