As a part of the sword study, it is necessary to describe the process of making a sword. This chapter explains only a very basic procedure of sword-making. It is a simple outline of the sword-making process since I lack expertise in the field.
When I was small, I used to see the process of metal being heated up in the furnace in my father’s factory. He owned a machine tool company and a forging factory. It was fascinating to see the metal was heated up, taken out of the furnace, pounded by two men, then put back in the furnace, and pounded again and again. To this day, I can still remember the exact color of the metal when it should be taken out of the fire. That was a strange thing to learn for a small girl. Not only that, it was dangerous for children to be close to the furnace when the metal was being heated. But those days, people’s idea for safety was different. I think the factory workers enjoyed seeing my brother and me being so impressed, so amazed, and regard them as heroes. We kept going to the shop until my father moved the factory to a bigger place. Today, I would never allow my grandchildren to be near a furnace.
The sword-making involves very many detailed processes, and each swordsmith has his secrets. Anybody interested in more detailed explanations, please refer to a book written by a famous swordsmith, Mr. Yoshihara Yoshindo, and a DVD made by his son. Their information is below. Mr. Yoshihara’s book is sold on Amazon. DVD is sold on Japan Amazon. DVD may be necessary to go through the proxy service; Zen Market since it is sold on Amazon Japan.
Book: The Art of the Japanese Sword —–The Craft of Sword Making and its Appreciation by Yoshihara Yoshindo, Leon and Hiroko Capp Published by Saviolo Edizioni
DVD: Katana/On Ko So Shin (温故創新)——-Katana project by Yoshihara Yoshikazu (吉原義一). Use proxy service-Zen Market, since only Amazon Japan sell it.
Tamahagane (玉鋼)
In the old days, the early sword-making time, swordsmiths extracted iron from iron sand and refined it by themselves for sword material. By the Kamakura period (refer to the timeline above), ironmaking was done by separate entities. Swordsmiths buy iron called “Tamahabane” from ironmakers. “Tamahagane” is the essential part of sword-making. “Tamahagane” is the iron made with the Tatara process, a unique Japanese smelting process.
Tama-Hagane from Mr. Yoshihara
Kawa-gane (側鉄) and Shin-gane (芯鉄 )
The Japanese sword is made from steel of two different hardness. Kawa-gane is for outer steel. Shin-gane for inner steel. Kawa-gane is harder steel, which contains about 0.6% carbon contents. Shin-gane is softer steel that has about 0.25% carbon content. Japanese swords are made with softer steel inside, wrapped around by harder steel, this way it is hard to bend, and hard to break.
Kawa-gane (側鉄: outer steel) ——– Shita-gitae (下鍛: Base forging)
Heat a block of Tamahagane → Hit with a hammer and make flat pieces → While Tamahagane is still hot, quench in water quickly → Break into small pieces.
Separately forge a rectangle plate with Tamahagane → Connect this plate with a handle or a lever to create a Teko → Stack up the previously broken metal pieces on the Teko carefully and closely. 
→ Cover the stacked up Tamahagane with ashes and clay for protection → Heat this in the furnace → Take it out from the furnace and hit with a hammer → Repeat this process many times to stretch out Tamahgane about twice as long.
While Tamahagane is still hot, make a notch in the center and fold in half → Continue the same process of heating up, hammering to stretch, and folding half (widthwise and lengthwise alternatively approximately 6 or 7 times depending on the original carbon level in Tamagahane). This process reduces the carbon content to the desired level.
Kawagane (側鉄: Outer steel) —– Age-gitae (上鍛: Finish forging )
At the end of Shita-gitae, chisel the block of Tamahagane so that it can be separated into two or three sections → Quench in water → Cool down → Break it into pieces along with the markings → Combine these pieces and repeat the heating, hammering, and folding processes.
Usually, the folding process is done 6 to 7 times for Shita-gitae (base forging) and 6 to 7 times for Age-gitae (finish forging). Total 12 times or so depending on the original carbon contents in the Tamahagane used. This process is for Kawa-gane (側金)
Purpose of heating hammering and folding
- Each time the heating and folding process is done, Tamahagane loses carbon content. For outer steel, the ideal carbon content should be approximately 0.6%. If the carbon content is too high, steel is hard, and as a result, the sword can crack. If it is too low, the sword will be too soft and can bend. Swordsmiths judge by their eyes to determine the right amount of carbon content. This is the professionalism and the art of sword-making.
- Removing slags and impurities from Tamahagane.
- Each heating and folding processes create many layers of thin steel that create the Ji-hada pattern (surface patterns like wood grain, burl look, straight grain, or a mixture of those)
Shin-gane (inner steel 芯鉄)
Shin-gane is the inner metal that is softer steel with less carbon. By having softer inside, the sword has flexibility. Having hard outer steel with higher carbon with softer steel inside prevents the sword from cracking or breaking. To make the Shin-gane steel, mix softer steel with Tamahagane. Repeat the same process as Kawa-gane.
Tsukuri Komi (造り込み) Sunobe (素延 )
Wrap the Shin-gane with the Kawa-gane, then weld two pieces together by heating, hammering, and stretch out to make a steel bar. There are several ways to wrap the Shin-gane, but the most common way is called Kobuse (甲伏). The illustration below is the cross-section.
The above photo (taken by my husband) shows a cross-section of a sword. Many years ago, a member of our sword club gave us a very rusty, damaged sword. My husband cut the blade and took the micro photo of the cross-section. This sword has a more complicated construction than the usual Kobuse method. It looks like it has 3 (4?) different hardness of steel. This sword seems it was once one of the top swords made by a top sword-maker.
Hizukuri (火造 )
Hizukuri is to make the final shape of the sword from Sunobe by heating and hammering. At this point, Ha (cutting edge) gets thinner, the Shinogi side gets higher, and it starts to form a sword’s shape.
Arashiage (荒仕上げ)
This process is rough finishing.
Tsuchitori (土取)
Mix clay, pine tree ash, ground stone, and water. Coat the sword with this muddy mixture. Scrape off a thin layer of the mix a little around the hamon area, then dry out. By doing the Tsuchitori process, hamon is created, and cutting-edge hardens at the same time.
Yaki-Ire (焼入れ)
After the muddy paste is dried, heat the sword evenly in the furnace. Judging by the heated sword’s color, pull it out from the furnace, quickly quench it in the water. Usually, this process is done after the sun goes down so that the swordsmith can see the color of the metal and can judge the temperature of the heated sword more accurately. This is the most crucial process since all the work done up to this point may be ruined if he fails to judge the heated sword’s precise color, water temperature, and quenching timing.
The final process is to send the sword to a polisher. The polisher called Togishi polishes and sharpens the blade. He brings out the beauty of the surface and the sharpness of the sword. This completes the whole process of sword-making. Every step is essential, but the polishers’ final process is as important as the rest of the work.
Study of Japanese Sword 