Kogatana Construction?

[Aiden CC]

Kogatana and kozuka are a part of koshirae I have always found interesting, and there is a feature of kogatana blades that has stumped me. On polished examples, it can be seen that one side has a hamon, meanwhile the other has file marks (yasurime?) and sometimes mei. This would seems to imply that only one side is hardened, as those features would be quite difficult to apply to hard steel (or they are applied before yaki ire, but they seem to be quite clean). 
 

Does any one know how the metal for a kogatana blade is put together? It seems like ni-mai with hardenable steel on one side and iron on the other is one possibility, or maybe the hamon is applied highly asymmetrically, hardening only the surface of one side? Any insights would be appreciated. 
 

Thank you,

Aiden CC

[mas4t0]

44 minutes ago, Aiden CC said:

It seems like ni-mai with hardenable steel on one side and iron on the other

 

Correct.

 

It cuts down on the amount of (expensive) steel required; kogatana don't have the strength requirements of swords, so steel is only required for the sake of edge holding.

 

As the iron is unhardenable you cannot get a hamon on that side, but it's easy to file and engrave.

[Aiden CC]

Thank you Mark, that makes sense. Composite structures seem to be the norm for blades of all kinds in Japan, so I figured something like that may have been the case. I do have one polished kogatana, but the construction isn’t readily evident, part of that may be that it came with some corrosion in various places. 
 

Aiden CC

[shakudo]

I find this interesting,as I did when I found a kogatana that was signed omote and dated ura- so I purchased it! Pretty sure there is a hamon. If interested I will find and post some pics?

Cheers

[shakudo]

Hi Aiden,

Just found this on yahoo.jp.

Its modern but shows hamon and mei and look closely you can also see the hamon on the omote! Mei cut in on non hardened material just like horimono!

Cheers

[Jacques D.]

the kogatana are made like the tanto (maru kitae); the difference is that only one side is polished and the other side except the edge is filed

 

https://www.Japanese-sword-katana.jp/kogatana/2210-6000.htm

[ROKUJURO]

On 9/17/2022 at 5:37 AM, shakudo said:

..... I found a kogatana that was signed omote and dated ura- so I purchased it! Pretty sure there is a hamon. If interested I will find and post some pics?...

Yes, please! Very interested to see it!

Jacques is probably correct with his statement. While TANTO are only hardened on the edge, they can be signed and embellished with HI or HORIMONO on the softer parts. KOGATANA are too thin and if indeed made in NI-MAI construction, they would harden through. So I think they are signed before YAKIIRE. 

[Franco D]

It must have been at least a decade ago now (?) that a seminar was held in Canada at Guelph University on forging Ko Gatana (if memory serves ). There must be some of the attendees still around, as well as examples that were made by the attendees, who would be able to describe the process exactly. Chris Bowen is where I would begin to find out more.

 

Ko Gatana, yes, made of skin steel. 

 

 

[1kinko]

It makes no sense to me that forge-welding two types of steel/ iron together is somehow easier than forging a mono-steel blade and quenching to form a hamon (but I must also admit that I don’t understand why only one side of a kogatana is polished). I have forged tsuba blanks from old kana blades (with hardened high carbon edges) and carved them, so carving a horimono on a hardened blade is not so difficult- the main difficulty is that any mistake or over/under-carving requires a lot of work on the remaining part of the blade.

[Franco D]

3 hours ago, 1kinko said:

(but I must also admit that I don’t understand why only one side of a kogatana is polished).

 

hmm,

 

Only guessing;

 

1. there's no hamon nor hada to reveal.

 

2. $130 per inch times one vs times two.

     ( I'd bet if if you're willing to pay to have it polished .... )

 

3. traditionally not done.

 

4. unpolished side provides surface for mei, horimono, other.

 

5. The natural patina that develops on the unfinished half provides contrast to the finished side.

 

[shakudo]

Hi  Franco,

Interesting.

Somethings I have been considering - the asthetic difference from side to side- colour and texture?

Also the retention of the mei( if its done before yakiire) by not polishing omote-even though nearly all are gimei or honorary?  

Lastly- friction- when fitted to the saya the top face( mei unpolished) rubs on the inside of the slot- usually horn( cant find name of it at the moment)- and the crude yasurime 'bites' so it stays in under friction. Why polish - regardless if it has a hamon when it will be just rubbed - waste of time and money really.

Just rambling thoughts!

Cheers

[ROKUJURO]

12 hours ago, 1kinko said:

I....I have forged tsuba blanks from old kana (KATANA?) blades (with hardened high carbon edges) and carved them, so carving a horimono on a hardened blade is not so difficult.....

Darrel,

this is not done in Japan. HORIMONO just go close to the YAKIBA, but not into it. Understandably at HRC 62!

In addition, if you use sword blades as raw material, there will be no hardness left after forging unless you harden it again (which makes no sense in TSUBA).

[1kinko]

Jean C- kanna blades are used in Japanese hand planes. I wasn’t saying horimono go into the hamon, only that one can carve into hardened steel.

 

Mike- the nagako on my kogatana are soft and flexible, the easier to keep attached within the kozuka. Is the steel in your double hamon modern kogatana soft and flexible? I like your idea of creating friction in the saya.

 

Franco- lots of blades with little hada get polished, I doubt the polishers in 1600 made $130/inch, the fact that it was not done doesn’t explain why it was not done, mei and horimono can be carved in hardened steel, who gets to appreciate the contrast between 2 sides of a blade? Have you seen evidence of a forge-weld on a kogatana? I don’t have a lot of them but I don’t see any evidence of 2 different steels, while I do see different colors between the soft and hard steel in kanna blades. 

I'm only playing devils advocate because I want to understand.

[ROKUJURO]

Hi Darrel,

thank you, I understand now (kana is not KANNA...).

The NAKAGO (not nagako) of KOGATANA are of course not hardened. In many cases you will find that they were slightly bent to fix them in the KOZUKA - not a very reliable construction!

You insist that carving hardened steel is possible, and I know it can be done nowadays with rotating tools and TAGANE with carbide tips. In traditional Japan, tools were made from high-carbon steel similar (or even identical with) sword steel. So I am curious if you could provide any samples of carving in hardened steel from that era.

[Franco D]

8 hours ago, 1kinko said:

Franco- lots of blades with little hada get polished, I doubt the polishers in 1600 made $130/inch, the fact that it was not done doesn’t explain why it was not done, mei and horimono can be carved in hardened steel, who gets to appreciate the contrast between 2 sides of a blade? Have you seen evidence of a forge-weld on a kogatana? I don’t have a lot of them but I don’t see any evidence of 2 different steels, while I do see different colors between the soft and hard steel in kanna blades. 

 

 

I should have said cost of polish times one vs times two. However, as I understand it the cost of an excellent polisher is ~ $130 an inch these days. Further, few Ko Gatana are worth a high quality modern art polish as they were made more for utility type purposes, rather than a quality piece as we've come to expect of nihonto, and with a honorary mei, but there are exceptions. As far as I can tell Ko Gatana are made of one piece skin steel. Which looks to be tightly forged. I wouldn't go as far as saying muji, but definitely very fine. Who gets to appreciate the contrast between the two sides? Hmm.

 

 

 

 

 

[DoTanuki yokai]

I don’t think there is a rule how to construct them.
In earlier times steel was expensive and now it’s Labour, this can change a lot. 

I have a knife where one side is very high quality polish while the other side is pretty rough. I did this because I will only sharpen on the rough side so the other stays nice.