Process of Forging & Shaping a Tanto Habaki

Once the blade is in rough polish, it is time to create a custom blade collar for it. This important piece of nihonto hardware is made specifically for each blade and is as complex as making a custom fit piece of jewelery. The function of habaki are three-fold; the primary purpose is to secure the blade in the wooden scabbard without any pressure on the blade itself, the secondary is to provide a solid shoulder against which to mount the handle and guard, and the tertiary is to provide a stiffened flex zone across the transition from tang to blade and decrease the chance of failure at that critical intersection.

A standard habaki is fabricated from two parts; the jacket, which appears to be the entire habaki, and the machigane, a small compound triangular prism shaped wedge that closes the gap where the hamachi bridges the edge and the nakago no hagata of the tang. Most of the habaki is formed by forging, the final adjustments by filing, and the joining of the two parts by soldering or brazing. Once the habaki is fit, the blade is ready for a handle and the accompanying koshirae.


Forging the Blank

A correctly formed tang and blade are necessary prerequisites to making a functional habaki. The widest point of the knife must be at the area where the blade and tang meet on the spine, and a gradual taper in both directions as well as towards the edge ensures proper strength, balance, and the ability to assemble (and disassemble!) the koshirae. One of the main design points when creating habaki is that they should be quite thin at the front, especially near the spine as that is where they will slide as they are sheathed and unsheathed.

Copper is by far the most common material for habaki, but other metals such as silver, shibuichi, and shakudo are also used. Subtle variation in shape and proportion can be used to complement a blade or mounting, as can various patinas, hammer textures, or chisel marks. With the exception of the initial bar shape, all forging is done cold in between cycles of annealing to soften the work hardened copper.

Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
A strip chisel cut from a reclaimed high voltage electrical bus bar, a source of very pure copper.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Hot forged into a bar of proper dimensions, this will likely yield enough to make two small habaki.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Cold forging out the taper in both directions from the spine (top to bottom, tang to blade) and leaving the thicker area above the mune intact.

Filing & Shaping

Forging in advance can save quite a lot of filing time later, and some judicious filing before folding can save a lot of trouble after the habaki is closed up. While the goal is to get as close as possible to the final shape, it is generally a good idea to leave some extra metal as the bending may not go exactly as planned.

Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Starting the notch for the munemachi is the most important step as filing it later is much more troublesome.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Using a chisel to remove it from the rest of the bar and cold forging the second side to match the first.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Cleaning up the back, note the thickness of the mune compared to the sides.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
This habaki will have a slight curve at the front, but there is plenty of excess metal here just in case.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
This butterfly is still pretty rough, but there is more forging to do after bending yet.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Using a tapered round punch on its side gives some radius to the inside of the mune. Concaving it slightly in along its length as well helps prevent it rocking on a high centre when the sides are bent up. Because it has been forged quite a bit already, this is as far as it will be bent before a second annealing cycle.

Bending & Fitting

The process of bending may require several cycles of annealing and forging depending on the accuracy of the original shaping. The sides are brought up and cold forged to the shape of the tang, being careful to work well back from the blade when hammering. When everything is fit well, the excess is cut and filed away and a small compound wedge called the machigane is forged and shaped to sit against the bottom of the tang in the gap where the habaki comes together.

Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
This is the second round of annealing during the bending processs, the habaki has already taken on much of its final shape and mainly needs to be thinned and adjusted at this point.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Most of the forging is done well back from the machi to avoid hammer contact with any part of the blade.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Cold forging the machigane from a scrap that was cut off the bottom of the habaki.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
A dry fit after filing it to shape, showing how the machigane will sit against the tang and the hamachi. The habaki will not be bridged by the machigane all the way to the front which will allow the edge to flow out of it.

Soldering & Finishing

Heated in a charcoal fire, hard silver solder is used to join the machigane to the habaki in such a way that the habaki is slightly too small to slide all the way up to the machi. Hammering the copper after soldering hardens the habaki as it stretches it to its final dimensions.

Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
The machigane in place before flux and solder are placed inside. A rusty steel wire provides pressure to the assembly, does not tend to stick to solder itself, and in this case makes a useful stand.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
When soldering in a charcoal forge, the air must be kept low and the piece placed away from the blast enclosed in a charcoal “oven” to create a reducing atmosphere.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Cooling slowly to ambient temperature avoids thermal shock that could cause the solder and base metal to pull away from one another.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
After soldering the copper has a layer of black copper oxide, as beautiful as it is, it is very brittle and would not stay intact during the final forging.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
In this case, a file was used to clean off the black copper oxide and create a subtle yoko-yasuri pattern. Then the habaki was reheated and very quickly transferred into hot water with a trace of borax in it. This type of fired copper is called hi-do (緋銅, fire copper), the technique causes stable red copper oxide to form instead of the brittle black oxide. The copper in the photo is fully cool, though it looks as though it is still glowing a beautiful red orange colour.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
The red oxide does not break off when forged and the habaki can be work hardened as usual, stretching it out to fit tightly in place.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
The fit at the mune machi showing how the slightly rounded hira/kaku mune style I am calling komaru mune continues into the habaki, rather than having the usual peaked iori mune shape. The habaki should follow the shape of the spine smoothly as it will rest there for drawing from and inserting into the saya.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
The final area to work with files is the shoulder that sits against the seppa, it should be square and flat, and should be at 90 degrees to the mune at the munemachi.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Waterstones are used to flatten and polish the shoulder, and usually the rest of the piece, but in this case the red oxide hi-do is the desired finish.
Island Blacksmith: Hand forged kotanto made from reclaimed and natural materials
Polishing with fine stones and charcoal is usually saved until after the tsuka and saya are made, but in this case the patina is already in place and must be carefully preserved during the other stages. Ibota wax is hand buffed onto the surface with a cotton cloth to deepen the colour and provide a glossy layer of protection.

The blade has its habaki, the next steps will be to create a seppa and tsuka.