Traditional Japanese swords are made from a material called tamahagane. The process of producing tamahagane is over a thousand years old. The technology of tamahagane production came to Japan via Korea and China. Since the earliest times, Oku-izumo in the San’in region has been the center of tamahagane manufacture in Japan. Before the 8th century, the archaic provinces, Bizen, Bingo, Bitchu and Mimasaka were collectively known as Kibi. Kibi lay upon one of the important trade routes that stretched across Japan and had always been a great production area of iron ore. In this ancient period the Kibi were a powerful people who had a strong economy based on rice culture, and were equal in power to the Yamato people who later united Japan and began the imperial line. It has been speculated that the legendary eight headed eight tailed dragon called Yamata no Orochi, in whoms tail was found the imperial regalia sword –Ama no Murakumo no Tsurugi (Kusanagi no Tsurugi) when he was slain by the storm god Susano-O in the Oku-izumo region, could be a metaphore for the tatara. A cherry red eyed dragon, from which swords are born.
By 1925, following the introduction of modern steel production techniques to Japan, the tatara-buki method was no longer used. However, with Japan’s activities in China and the approach of WWII, the demand for traditional Japanese swords for the military was the catalyst for the resurrection of the tatara-buki method. In 1933 at Yokota-cho, Shimane prefecture the Yasukuni tatara was constructed to provide tamahagane for the Nihonto Tanren Kai at Yasukuni shrine in Tokyo. Unfortunately, the tatara was once again closed due to Japan’s defeat at the end of the war in 1945. After the confiscation and near destruction of Japanese swords by the occupying allied forces, the Nihon Bijutsu Token Hozon Kyokai (NBTHK—The Society for the Preservation of Japanese Art Swords) was formed. One of the objectives of the NBTHK was to preserve the Japanese sword and its production as a traditional culture. In 1976, with the support of the national treasury, the NBTHK re-instated the tatara to its former glory by using the underground structure of the former Yasukuni tatara, where it is overlooked by the shine of the patron Shinto deity of metal Kanayago-kami. Consequently, the minister of education designated tamahagane production as a Traditional craft for preservation.
By 1977 the then Finance Minister Toshiki Kaifu had designated the Nittoho Tatara as a site of selected conservation techniques worthy of preservation. Restoration was completed on November 8th 1977 and a ceremonial firing ceremony of the tatara was performed in the presence of the Crown Prince Takamatsu (Honorary President of the NBTHK). Then, on the 18th day of the same month the first operation of the new tatara was carried out. As well as being the main source of tamahagane production for Japanese swordsmiths, The NBTHK (also known as Nittoho) also train craftsmen in tamahaganeproduction. The knowledge of murage has been passed down from teacher to student over a long period of time. Former murage (tatara operators), the late Abe Yosizou and Kumura Kanji were appointed as authorised conservators of the traditional craft of tamahagane manufacture. The current holders of this title are the current murage at the tatara Kihara Akira (appointed in 1986), and Katsuhiko Watanabe (appointed in 2002).
The base material from which tamahagane is produced is called satestu—sand iron (fe). Satetsu is collected from the chugoku region of Japan. It is taken from the riverbeds during spring and summer and mined from the mountains during fall and winter. This is so as not to disturb the local farmers by polluting the rivers during crop seasons. The process of producing tamahagane is called tatara-buki in which a large clay furnace, called a tatara, is used to smelt the satetsu. To produce optimum tamahagane it is important that all moisture is removed. To combat this, the tatara smelter is built on top of a large 3 metre deep underground structure. The structure includes air ducts, called ko-bune, through which the moisture is drawn out during the manufacture process. In addition, the tatara is usually only operated in late January, early February every year, when moisture levels are at their lowest.
The tatara usually operates for three weeks. This is enough time for three cycles: one cycle taking seven days to complete. Day one is ground preparation. A layer of ash and charcoal is compacted by two rows of men facing each other with 12 ft wooden poles and take turns to beat the ground in a ritualised manner in order to compact the ash and charcoal in order to make a solid base on which to build the clay furnace. Day two, clay, excavated from nearby, is shovelled into a cast to make large clay bricks, then placed over the substructure and built up into a rectangular shape. Then some charcoal is fired up inside to dry out the construction.
Day three, four and five, The main phase of the tatara operation takes three days and nights This is the non-stop cycle of smelting sand iron and charcoal by adding it every thirty minute for 72 hours. The temperature in the furnace kept at around 1500° C. The murage checks the condition of the melting sand iron by inspecting the molten slag that is expelled through vent holes at the ends of the clay furnace. By the end of the process, some of the initial 20-40 cm thick silica furnace walls have reduced to around 10 cm becoming incorporated into the smelt, producing tamahagane along both the sides of the kera where the air supplied by wooden pipes pumped in by the automated bellows provided optimum deoxidization.
When the time is right, on the order of the murage, the walls of the tatara are torn down and a large rectangle of steel called a kera is revealed.The kera is approximately 2.7 meters in length by one meter wide and 30cm deep, weighing between two and two and a half tons.This is left to cool and later dragged out to another workshop where on day seven it is broken and graded by hand before it will be distributed to swordsmiths. The next day the cycle begins again.
First grade tamahagane
Has an even of carbon content distribution of 1-1.5%.
Has a carbon content ranging between 0.5-1.2%
Is identical to first grade tamahagane, but is in pieces no larger than 2cm.
Has a carbon content over 1.75 carbon and can be melted.
Is a mix of pig-iron, steel, semi-reduced steel, slag and charcoal etc.
Is identical to second grade tamahagane, but in pieces no larger than 2cm.