August 2009 Alumni Kajioshi and Bonji Courses, Oroshigane Seminar
- September 19th, 2009
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Last month, we were thrilled to have four alumni of Tomboyama Nihonto Tanren Dojo return to the school to attend our August 7-9, 2009 Oroshigane Seminar.
Unscheduled August 2009 Bonji and Kajioshi Courses
Three alumni joined us two days earlier for special unscheduled two-day classes in bonji and kajioshi.
Students Jeff and Allen carved bonji in blades they had forged themselves of folded cable and Steven studied blade shaping and practiced achieving subtle refinement of shape on the water stones.
August 2009 Oroshigane Seminar
“Oroshigane” is a Japanese term used of the processes a smith uses to adjust the carbon content of sword steel, and also used to refer to the steel made from such processes.
For the seminar, we began with two forms of iron, electrolytic sponge iron and antique wrought iron, which we added carbon, through the process of carburization, to create steel.
Both electrolytic sponge iron and antique wrought iron are extremely pure forms of iron. In Japan, electrolytic sponge iron is known as denkaitestu, and is sometimes used for oroshigane by swordsmiths who cannot attain tamahagane, or are interested in making their own steel. Electrolytic sponge iron is literally “distilled iron”, a byproduct of the electric arc furnace.
True wrought iron is an antique form of commercially pure iron. Although many products are described as wrought iron today, such as guard rails and gates, they are made of actually made of mild steel and only retain that description because they were formerly made of wrought iron. Because of it’s corrosion resistance, wrought iron was often used for marine applications in the past. Like denkaitetsu, wrought iron is an extremely pure form of iron, although it is also high in silica. It is distingiushable from mild steel by its fiberous grain. Because it is no longer made on the industrial scale, wrought iron is sometimes jokingly called “unobtainium”.
Modern steel contains several alloyed metals and impurities, not found in nihonto. Some impart desirable qualities or counteract the effects of contaminents. Most important of these is manganese. Manganese prevents phosphorus (an embrittler) from migrating to grain boundaries and creating weaknesses, and also promotes deep hardenig. But manganese also makes steel shinier and more reflective, two qualities which make an sword forged from modern steel instantly discernable from a traditionally made Japanese sword. By beginning with a very pure sources of iron and adding only carbon, we are able to produce a steel that is compositionally the same as tamahagane and visibly indistinguishable.
