This tanto began as a reclaimed carriage spring and was hand forged in a pine charcoal fire, smoothed with files and a sen scraper, differentially hardened using traditional water quench yaki-ire with clay, and polished by hand with natural Japanese water stones.
The source for this steel was a former homestead site in Alberta.
The raw material for this blade spent the last century as a leaf spring for a horse-drawn carriage.
Sunobe: Forging the Blade Pre-form
Rough forging of the rectangular sunobe (pre-form) nearing its final form, sunobe sets the tapers and determines the approximate dimensions of the finished blade in all directions (thickness, width, length). Note that the edge area is facing upwards as the tip has not been turned up yet.
Rough sunobe compared to the original piece of steel from the opposite side of the spring, the volume is from next to the hole to the cut-off on the right.
Hizukuri: Forging the Bevels
From the rectangular sunobe the bevels are now forged in giving the final size and three dimensional shape to the blade, all shaping is only hand hammer work up to this point.
Arashiage: Rough Filing the Shape
After setting the machi (tang notches) and cleaning up the profile with hand files but before scraping and filing the bevels, the sides are still as-hammered.
Tsuchioki: Applying the Clay
After scraping and filing the bevels flat a thin layer of clay coating is applied in preparation for yaki-ire (hardening).
The clay layer will delay cooling by about half a second, causing the body of the blade to remain tough while the edge is hardened.
The placement will not be exactly where the clay stops, but will depend on the temperature, blade geometry, and alloying ingredients in the steel as well.
Yaki-ire: Quenching
Pre-heating the clay slowly helps prevent it from cracking at higher temperatures.
Heating the clay-coated blade in preparation for quenching in water. It is first heated edge up to protect the thin area and then edge down as the critical temperature approaches.
After a successful water quench, the edge has hardened and the blade has not cracked or warped.
The blade must begin with a small amount of reverse/downward curvature in order to compensate for the forces of yaki-ire and end up as a straight-spined blade.
Checking the hamon placement with a coarse waterstone after yaki-ire (hardening) and yaki-modoshi (tempering), a well-proportioned old style narrow suguha (straight) hamon is revealed.
Waiting in the shiageba (at top of rack) after removing the remaining material along the edge and shaping the rough edge geometry using course waterstones.
A Look at Tanto Geometry
A view of the omote side. A kata is used to form the profile of the nakago. Converging lines should be straight, or very slightly concave on the nakago-no-ha as they taper towards the tip.
The nakago-no-ha is set to a constant width based on the width at the hamachi, approximately 2mm. Ways to keep it as close to 2mm as possible are to deepen the hamachi slightly, leave more haniku (“edge meat”) in the form of a slightly more convex bevel, or leave an ubuha (an unsharpened area where the edge is a bit thicker tapering off for a couple of cm after the hamachi)
As the tang bevels follow the blade bevels, the nakago-no-mune should taper slightly towards the tip. A slight convex here will help the fit of the habaki on thicker blades. Note that the thickest point must remain at the machi in all cases.
The nakago-no-mune and the nakago-no-ha are given a very slight radius with a file to finish the shaping.
A view of the ura side. Blade polishing should extend to include all the area that will be covered by the habaki.
A view of the omote side of the kissaki. A flowing line narrows the blade subtly and then curves seamlessly towards the tip.
The mune at the kissaki. The distal taper smoothly merges into a convex or tapered kissaki towards the tip. The style and intended purpose of the tanto will determine the amount of ha-niku (“meat” behind the edge) along the bevels and the tip will often reflect this geometry.
The iori mune at the machi. This example is about 8mm at the machi and tapers a little over 1mm per side towards the kissaki, again depending on the style and purpose of the tanto, but usually in the 70% range.
The ha at the machi. The edge has not been fully established, but the swelling of the ubuha is visible over the last 4cm or so. Ubuha should never be enhanced in subsequent polishings or the appearance of fumbari will suffer.
The omote side at the machi. Note the slight swelling creating fumbari as it approaches the machi.
A view of the ura side. Final blade polishing should extend to include all the area that will be covered by the habaki.
The blade has a hira-zukuri profile, suguha hamon with elegant turnback, an iori mune, and an ubuha (unsharpened portion near the hamachi). The blade is just about 11.5″ long and the spine is 8mm thick at the machi.
Specifications
長さ/刃長 Nagasa: 9 sun 5 bu 5 rin (289mm)
元幅 Motohaba: 8 bu 2 rin (25mm)
重ね/元重 Motokasane: 2 bu 5 rin (8mm)
反り Sori: muzori (no curvature)
中心/茎 Nakago: 3 sun 5 bu 5 rin (107mm)
形 Katachi: hira-zukuri, iori-mune
刃文 Hamon: suguha, with ubuha
帽子/鋩子 Boshi: ko-maru
中心/茎 Nakago: futsu, kuri-jiri, one mekugi-ana, signed near the tip
銘 Mei: hot stamped katabami-ken kamon
