During the hardening process the clay layer causes a split second difference in cooling time which creates two different hardness areas in the same piece of steel. The edge cools faster and forms a very hard steel structure called martensite while the body cools slower and forms a very tough steel structure made of ferrite and pearlite. The boundary between these two areas is called hamon and is commonly seen as a frosted line down the length of a polished sword blade.
more about the process of yaki-ire
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First Lighting of the Forge & Antique Habaki Utsushi (写)
First lighting of the newly rebuilt charcoal forge in the island kajiba followed by stamping the tang and then hand forging and filing a classical tanto style habaki, silver soldered in the charcoal forge and closely based on an antique Edo period habaki. An utsushi (写) is a closely based study of another work for the purposes of professional development. Polishing and patinating will be done after the saya has been carved. information about the machigane | habaki making process
SOTW #21 – First Lighting of the Forge
First lighting of the newly rebuilt charcoal forge in the island kajiba. The first operation was to heat a tanto tang for stamping. Because it had already undergone yaki-ire, the blade had to be kept cool during heating to protect the temper. watch extended version | island forge kajiba project
SOTW #20 – Assembling the Furusato Tanto
This discarded block of wood from the Congo/Zaire sat for several years waiting for the right blade to make the best use of it. This precious dark chocolate coloured hardwood is locally called Tshikalakala or Dikela, meaning turn around or circle back, and this particular piece has a slightly curving grain that follows the line of the saya. The name Furusato (故郷) means home place or hometown and contains the ideas of being rooted or grounded wherever one may sojourn, and a confidence and longing for return. more about this project
TLDW #24 – Making an Ireko (nesting) Saya
An ireko saya (入れ子鞘, nesting scabbard) is a lining inside the saya which protects the blade from the hardwood. Furusato (故郷) means home place or hometown and contains the ideas of being rooted or grounded wherever one may sojourn, and a confidence and longing for return. This tanto has a simple and elegant form with a natural and humble mounting that reflects the rustic satoyama lifestyle and suits the aesthetics of the way of tea. more about this project
Building Simple Charcoal Forges
Building two examples of quick and simple sideblast charcoal forges with found and reclaimed materials to demonstrate that lack of equipment and materials should not be a major obstacle.
Ways to improve and expand on these concepts include: mixing copious amounts of chopped straw or charcoal powder (6:2) into the clay to make it refractory, using high temperature kiln bricks, making the walls higher and longer, using the clay to narrow the tuyere to about 1sun/3cm right where it enters at the bottom side of the forge, putting a barrier up to protect the fuigo (and allowing a shorter pipe), allowing the clay to dry before lighting the forge, etc.
Learn more about fuigo, a full traditional swordsmith forge build, or a smaller tanto forge design.
Glass Top Fuigo – Inside View of Box Bellows
A look at the inside operation of a prototype fuigo (鞴) box bellows…four wooden flap valves (called ben / は弁), two for intake and two for the manifold, control the direction and location of the airflow on each stroke of the piston to provide double action to the single output into the fire.
Differential Hardening Sunnobi Tanto
Sunnobi tanto are larger than ordinary tanto (nagasa above 1 shaku) and may have sori similar to ko-wakizashi. Read more about the process of yaki-ire.
1. Using approximately a 1:1:1 mixture of natural clay, polishing stone powder and ground charcoal to mask the back of a hand forged blade about 1-1.5mm thick to slow down the cooling rate.
2. Brushing on a thin slip layer with extra charcoal added along the exposed edge to speed up the cooling rate and protect from carbon loss.
3. Carefully heating in a charcoal forge supplied by air from a fuigo box bellows until the edge reaches critical temperature.
4. Plunging edge-first into cold rainwater to cool the blade quickly and harden the edge while leaving the rest tough and resilient.
5. Testing for successful hardening with a file and then removing the clay with a mild steel scraper.
6. Slightly reheating the blade over the flames to temper the edge.
7. Test polishing on a coarse Japanese waterstone to check the hamon.
Process – Making habaki with simple tools
Making a habaki from reclaimed copper. Material is scrap copper from an electrical bus bar, forged and bent to shape, silver brazed with hard silver solder in the charcoal forge with fuigo, finish work done with files and rasps. Watch the shorter overview edit here.