Just a thought on Japanese burnishing...

[Al Massey]

I was thinking, recently- dangerous, I know- I wonder if one of the reasons for burnishing the sides/backs of Japanese blades was to impart a level of work-hardening to an otherwise soft surface, so that in practice or in dueling those areas might get less scarred if parries were done with those parts of the blade?

[dan pfanenstiel]

I don't think so, Al. The burnishing would do little or nothing for blade to blade contact. Intreresting question though. In all my reading and research I don't recall a reason for the burnishing. I would guess that it was a visual thing that caught on, maybe in the later era, much like hadori polishing. It just seems like a technique to highlight the shinogi. I can't imagine burnishing on a blade meant for combat.

Dan

[Al Massey]

6 hours ago, dan pfanenstiel said:

I don't think so, Al. The burnishing would do little or nothing for blade to blade contact. Intreresting question though. In all my reading and research I don't recall a reason for the burnishing. I would guess that it was a visual thing that caught on, maybe in the later era, much like hadori polishing. It just seems like a technique to highlight the shinogi. I can't imagine burnishing on a blade meant for combat.

Dan

I'm not so sure. Although nihonto were quite hard at the edge, most of the time the back was very soft indeed- from everything I've found an RC 20 or less would be normal in those areas, and even a minor amount of surface hardening would be a good thing for parries. Although most open warfare had stopped in that period, duelling was still quite in vogue.

[dan pfanenstiel]

Mune-yaki, or hardening of the spine would be much more effective than burnishing for combat parrying, so I still don't think so. I could be wrong. I checked some of my books and still couldn't come up with a reason for burnishing. I'll ask around, as you've piqued my interest :-)

Edited February 18, 2019 by dan pfanenstiel

[Al Massey]

Hardening of the spine might be more effective, but you might also increase the odds of cracking both in the quench and in usage, especially imho as not much in the way of tempering was done with these swords. I could be wrong, but I don't think nihonto were tempered past a very cursory stress-relief in order to keep a very hard cutting edge.

[Emiliano Carrillo]

So as I understand it the reason is indeed the same as kesho polish. A burnished shinoji looks more crisp even if the polishing lines are themselves not sharp. The actual meeting of lines between shinoji and ji is a very important point in the polish and can be rounded out and softened easily. The reasoning I have heard for kesho is that smiths were at that point making rather uninspired swords and they needed a way to spice up the 800 year old blades that had been polished down almost to nothing over the years as well as make the newer swords look stronger and more virile. I imagine burnishing would be the same, a way to gloss up the blade and add more interest visually. As I understand it, burnishing was not done in older periods, and blades themselves were probably not 'art polished' like they are nowadays. A tool for using ends up with damages, and having a very costly polish damaged every time you went into battle would just have the average samurai in the poorhouse trying to maintain their sword properly. I have done a fair bit of burnishing on my own work and also on nihonto, and it does not require much force, instead it is a gentle work. It would not help to harden the surface by any amount I think. The nihonto I have in my collection all have between 58-62 RC for the edges, with the spines being too soft for my chisels to get an accurate reading on them. 

[SteveShimanek]

The grain on the shinogiji on many swords tends to be rather open, and burnishing helps to somewhat close the grain and provide a brighter finish than stones can. I agree that burnishing has a negligible effect on hardness for parrying.....most sword schools taught to avoid sword to sword contact according to what i have been taught, though contact is common in kendo and bokken work.

[dan pfanenstiel]

I asked a friend, who's dealt with nihonto for more than thirty years, and he thinks the functional benefit to burnishing is to minimize scuffing of the mune and shinogi-ji (if there is one) when entering and drawing from the saya. Otherwise, he mirrored what's been said about it being a later period "fashion" thing, like hadori style polish. I personally could take it or leave it. Looks good when done well, but I like to see the steel and it's flaws too.