Utsuri Utility

[Cameron]

I forget where I read this, maybe Nakahara, but on the subject of utsuri, lost and found ,etc 

 

-was it a reflection of better ability to withstand impact trauma?

[SAS]

I always thought it was just a artistic appreciation thing, but I am willing to be corrected if wrong.

[Apercus]

Back when I was examining the metallurgy of Nihonto I came to the conclusion that most utsuri was a microstructure called banite which is almost as hard as the martensite at the edge but much tougher. It would give the blade improved strength and hardness. Banite forms at a slightly lower temperature than martensite which means the blade was not uniformly heated to the same temperature. I found it was more plentiful on medium carbon content steel but I can’t say that is true for all alloys. I believe many of the older koto blades were San mai with medium carbon content in the outside layers. It’s just my speculation but perhaps that’s why utsuri is more common in some schools and periods. All of that is just my two cents worth from a little bit of experimentation a long time ago. I’m sure there are more knowledgeable people here.

[PNSSHOGUN]

I had always believed it had something to do with the construction of the sword.

[Apercus]

Sorry, I forgot to sign again.

Shannon Hogg

[Valric]

From what I've gathered in my studies, Utsuri denotes a particular steel structure of intermediate hardness between the brittle edge and the soft interior and back. I do faintly recall it entailed a second, softer quench, which also had the effect of stress relief.I can't recall the specifics but it was clearly a functional innovation. I'm sure someone here can say more about the technical details. 

 

Bizen steel is reputed to be quite soft, I do remember polisher testimonies which state that utsuri areas are of 'intermediate hardness' and I think this fits well with the idea that to maximize structural soundness you want graduated transition between brittle and soft, and I think this was the function of Utsuri. 

 

Now, it could be specific to Bizen, not in the sense of the innovation per se but in the sense of its necessity given the raw materials that this school had to work with. Perhaps the unhardened part of the Bizen steel was so soft that this led to too much bending - so rather than to change the procurement of raw materials, they implemented a second hardening stage to palliate for the deficiency of their ore and this led to Utsuri. 

[Apercus]

Interesting. Everything you say about historical blades sounds right. There may be multiple and differing things we call utsuri or multiple ways to produce it. I only did a limited amount of experimentation and I no longer have access to X-ray diffraction and an electron microscope or the energy to work long hours at the forge. I can only say the method I use to reliably produce banite/utsuri is by heating only the edge of the blade past the transition temperature and by alloy selection. Yoshida Yoshihara describes this very process in “The Craft of the Japanese Sword”. There’s not a lot else written about it that I can find other than some technical journals about banite formation. Maybe someone will experiment a little and publish results.

Shannon Hogg

[O koumori]

Kokan Nagayama in Connoisseur's Book of Japanese Swords says:

 

"The purpose seems to have been to improve the sword's flexibility to prevent breakage during use. Usually made of steel that is softer than the rest of the blade's surface."

 

Dan Kedzie

[Gakusee]

It has been covered and discussed multiple times before on this forum, in books and elsewhere on the WWW.

Markus Sesko does a very good job of explaining the interplay of carbon content (hard-soft dichotomy) versus the quenching temperature (nie versus nioi utsuri). Both are important to grasp when trying to understand utsuri.

 

So, more reading and more research are needed by people trying to learn.

 

 

See: https://markussesko.com/2013/08/22/some-thoughts-on-utsuri/

[Kanenaga]

For spectacular Bizen-style utsuri, take a look at the Kagemitsu tachi currently on Darcy's website.

 

https://yuhindo.com/osafune-kagemitsu-tachi/

[Gakusee]

For spectacular Bizen-style utsuri, take a look at the Kagemitsu tachi currently on Darcy's website.

 

https://yuhindo.com/osafune-kagemitsu-tachi/

That and the Nagamitsu and Norifusa and so on

[Valric]

Confession: I discovered thanks to Darcy that what I always thought was Utsuri was, in fact, the darker antei part. 'shadow of the hamon' is a very bad way to describe Utsuri because it makes one think it has to be the dark part. In fact, 'reflection of the hamon' is the better descriptor to avoid misleading guys like me. This means that what I said above applies to the 'antei' not the Utsuri. The antei is the area of transitional hardness. 

[SAS]

In the era of combat with swords, practical testing would reveal which methods yielded more useful swords; utsuri may have been a by product of particular hardening techniques, that was then replicated for its utility.