how hard is the edge?

[Tokaido]

Hi nihonto friends,

after the auction is over, I like to ask the group for comments about the hardness of a swords edge.

http://www.ebay.com/itm/Japanese-SAMURA ... 7675.l2557

 

The pictures show more dents than chips. I'm especially curious about the "bigger" dent. How soft is the edge on a Sue-Soshu blade??

I expected a much harder edge!

Anyone seen this before?

 

Greatings

Andreas

[Stephen]

whats the old saying "you could park a bus in that fukure"...sorry if a member bought this, a good togi might be able to take care of it.

[Marius]

The edge looks odd. As if it was soft iron, not hard steel. No chips, just dents. Very strange.

 

Ah well, eBay again...

[Eric H]

How soft is the edge on a Sue-Soshu blade??

Neither the period of manufacture nor the the school have an influence on the hardness of an edge, all depends on the skill of the smith. Any properly made sword from tamahagane has by performing yakiire a very hard edge. A study of microstructures on a cross section: a small piece was cut from a Muramasa 2nd.gen. blade. The maximum hardness of the sharp edge was 720-730 HV.

Other researchers had reported the maximum hardness level in sharp edge (other swords) was about 700-820 HV. It is found the hardened area is limited to sharp edge and a few distance from the sharp edge decreases hardness drastically. (EDP Sciences, 2009)

 

HV = Vickers hardness test

 

Eric

[Stefan]

72 Points at NTHK shinsa fore this blade ?

No more questions....

[cabowen]

The hardness of the edge depends on several factors: the carbon content of the edge steel, the cooling rate, and the tempering done post quench.

 

Most koto blades that I have seen tested in the literature have in general been shown to be softer (lower rockwell hardness) than later blades. This has been attributed to a lower carbon content of the hagane in general. Many times one will see a rolled, rather than chipped edge in these blades. This blade shows both a rolled edge in the kissaki and some chipping in the monouchi. This is rather typical for a sword of this period.

 

A blade can lose hardness if it is exposed to high temperatures, and loose the yakiba completely if it spends sufficient time at a high temperature (as in a fire). Some blades have been heated enough to soften them. Usually the ha becomes rather indistinct as a result. Often this happens in the kissaki.

 

This blade should polish fine and the chips and rolled edge will be repaired. I'm not certain that has been called a fukure is in fact a fukure. Without seeing the sword in hand, I hesitate to say exactly what it is...The shape and sharpness of the edges make it look like it may be some sort of inflicted gouge.

 

Ubu, signed, Muromachi era blade at 72 points? I find nothing wrong with that assessment.

[Darcy]

I agree with Chris.

 

Kenji Mishina also commented to me, and probably other polishers can comment, that Shinto steel generally takes to the stone differently because of the hardness involved. Kenji Mishina remarked that he found only Sukehiro to be different and he could tell his swords when polishing them by how they responded to the stone under his hands.

 

It seems that in general the koto makers were more concerned about durability, even when it comes to Soshu blades that have a lot of nie. Also it is possible that having been polished more often they have less of the hardest steel remaining on them. Or maybe a combination of both.

 

I wouldn't be surprised if the Shinto makers, in a time when swords were not going out and being smashed up every day, put more emphasis on making a sword that could take and hold a razor's edge better. These would be more brittle, but if you wanted to do a one time demo of cutting ability they would perform very well.

 

In the koto period a sword that was able to get that fine edge but chipped rapidly and more easily would likely cost you more in replacements over time. I tend to believe in form following function most of the time, and I see economic benefits in both periods for Shinto makers to prefer harder steel and Koto makers to prefer more resilient steel.

 

It reminds me a bit of an anecdote about the AK-47 compared to the first versions of the M-16. The AK-47, loosely and simply made, would seem to be easily outclassed by the first versions of the M-16. But the simple manufacture and loose tolerances on the AK-47 suited itself to situations where the user couldn't afford or be able to have it undergo constant maintenance. If the bolt rusted you could give it a kick and you would most likely be back in business. Where the first versions of the M-16 proved very difficult to maintain in the field. This is not to draw a parallel between these models of guns and the periods of sword making, but more that the idea of what you design for performance in the lab or at the testing range may not be ideal for repeated and realistic use in the field.

 

And that would probably point again to resilience being emphasized on koto works compared to simply outright sharpness at the edge.

[cabowen]

The most basic explanation given by most experts for the tougher edge seen in koto blades in general (along with hamaguri-ba/hira niku) is that koto blades were made when armor was apt to be worn while in later periods this was not the case. Thus, Shinto and shinshinto have harder, less tough edges that retain sharpness (for use against softer targets and less hira-niku).

 

The tougher steel in koto does make them a bit more durable; the idea though that the edges have become softer because harder steel has been removed is false. As long as the yakiba remains, it is of the same hardness throughout at the edge.

 

Soshu is said to have evolved at the time when Mongol invasion was a threat. They used a tough leather armor which was different than that typically used by the samurai, As a result, they attempted to adapt the shape and hardness accordingly to make the swords more effective against such targets. While it makes sense and is an oft repeated story, I have no idea if it is based in fact.