As a part of the sword study, it is necessary to know the construction process of sword making. But it is a very involved process and each swordsmith has his own secrets, this chapter only explains the very basic procedure. Anybody interested more detailed explanation, please refer to the book written by a famous swordsmith, Mr. Yoshihara Yoshindo and DVD as below. You should be able to buy this book and DVD from Amazon. If not, contact me. I can order from the author directly.
The art of the Japanese Sword ————-The Craft of Swordmaking and its Appreciation by Yoshihara Yoshindo, Leon and Hiroko Capp, published by Saviolo Edizioni.
DVD: Katana / On Ko So Shin —–Katana Project by Yoshihara Yoshikazu(吉原義一）
Tamahagane (玉鋼 )
In old early sword making time, swordsmiths himself created the steel for sword material by collecting the iron sand and refined himself. By the Kamakura period, steel making was done by a separate entity. Swordsmiths buy steel called “Tamahabane” from a steelmaker. “Tamahagane” is the most important part of the sword making. “Tamahagane” is the steel made with the Tatara process, that is a unique Japanese smelter.
Kawa-gane(側金) and Shin-gane(芯金 )
The Japanese sword is made from two types of different hardness steel. 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 a softer steel which contains about 0.25% carbon contents. Japanese swords are made with the harder steel outside and softer steel inside therefore, does not bend, does not break.
Kawagane (outer steel側金) —– Shita Gitae (Base forging 下鍛)
Heat up a piece of Tamahagane —– Hit with a hammer and make a flat piece—– While Tamahagane is still hot, quench in water quickly —– Break into small pieces —– Separately, forge a rectangle plate from Tamahagane —– Connect this plate with a handle (or a lever called Teko) —– Stack up the previously broken metal pieces on a Teko (handle or lever) carefully and closely.
—– Cover the stacked up Tamahagane with ashes and clay for protection purpose —– Heat this up in the furnace —– Take it out from the furnace, 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 back into half —– Continue the same process of heat up, hammer to stretch out, fold back (half in sideways and half in length wise alternatively approximately 6 or 7 times depends on the original carbon contents in Tamagahane). This process reduces the carbon contents to the desired level.
Kawagane (outer steel側金) —–Age Kitae (Finish forging上鍛 )
After Shita Gitae, the block of Tamahagane is chiseled to divide into two or three sections —– quench in water —– Cool down —– break into pieces where marked before —– repeat heating, folding, hammering 6 or 7 times, depends on the original carbon contents in Tamagahane. This process is for Kawagane ( 側鉄 )
Purpose of heating hammering and folding
- Each time the heating and folding process is done, Tamahagane loses carbon contents. For outer steel, ideal carbon contents should be approximately 0.6%. If the carbon contents are higher, 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. A swordsmith judge by his eye to determine the right amount of carbon contents. This is the professionalism and the art of the swordsmith.
- Removing the slag and impurity from Tamahagane.
- Each heating and folding processes create many layers of thin steel that create the Jigane pattern (surface patterns like wood grain, burl look, straight look or mixture of those)
Shingane (inner steel 芯金 )
Shin-gane is the inner metal. By having the softer inside, the sword has flexibility. Having hard outer steel, it prevents to crack or break. To make the Shin-gane steel, mix softer steel with Tamahagane. Repeat the same process as Kawa-gane.
Sunobe (素延 )
Sunobe is the process to wrap the Shin-gane with the Kawa-gane then weld two pieces together by heating, hammering and stretch out to make a steel bar like. There are several ways to wrap the Shin-gane, but the most common way is called Kobuse (甲伏). Illustration below.
Hizukuri (火造 )
Hizukuri is to make the final shape from Sunobe by heating and hammering. At this point, Ha (cutting edge ) gets thinner, Shinogi side gets higher, and starts to form the shape of a sword.
Arashiage (荒仕上げ )
This process is rough finishing.
Mix clay, pine tree ash, ground stone and water. Paint this muddy mixture on the sword. Around Hamon area, remove a thin layer of the muddy mixture a little, then dry out. By doing Tuchitori process, Hamon appears and cutting-edge hardens at the same time.
After the muddy paste is dried, heat up the sword evenly in the furnace. Judging by the color of the heated sword, pull out the sword from the furnace then quench into 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 better. This is the most important process since all the work done up to this point may be ruined if he fails to judge the precise color of the heated sword, water temperature and the timing of quenching.