Defining Nihonto

[nagamaki - Franco]

An article written by Mr. Tanobe for your new or perhaps repeated interest. Enjoy!

http://www.arscives.com/historysteel/japaneseintroduction.htm

[Eric H]

Jigane 地鉄 “iron folded 100 times.”

Eric

[Carlo Giuseppe Tacchini]

Hi Eric.

 

It is possible the statement has not to be taken literally but in a more general meaning.

Possibly a slip by the translator, but what comes to mind to me is the inscriptions of quality control that antique chinese swords had to have when produced, that stated various numbers of "foldings" (being 100 the highest level of quality) that in reality meant the equivalent in "layers". Some of such ancient chinese swords were sectioned and the number of layers of the 3 sections of steel they were forged, when added to each other, almost exactly matched the number of supposed "foldings". Maybe it's his way to say "top quality forging".

 

My 2 cents.

[Eric H]

Hi Carlo,

 

Folding times and layers are two different things as you well know. In modern swordsmithing the first six foldings are called shita-gitae, they are followed by additional foldings, but as I remember that should not exceed 15 or 18 folds at maximum, for the steel gets weak and looses the pattern, hence a loss of its quality...this is valid of course also for old Nihonto.

Normally a sword has around 32000 layers.

 

But maybe I have misunderstood something.

 

Eric

[Curgan]

Although, I can't document this, I think there is an *urban legend* that Japanese steel is folded 100 times. However, I don't xonsider this plausible, because it would result in homogenising the steel and a consequent loss of the hada...

[Carlo Giuseppe Tacchini]

I was suggesting to read it not literally but as a "way to say", originally meant to indicate

a top level forged blade :

 

Page 10 here :

 

http://www.webalice.it/tsubame1/Downloads/1)%20On%20the%20origins%20of%20Nihonto.pdf

[Jean]

Japanese steel is folded 100 times.

 

= one hundred times 2x2 ===> steel would lose all its quality. Maximum I have read was arounf 15/17 times folded (2x2x.... 17 times)

[Jacques]

That depends of Era and School and of course of hardness of steel.

[Ted Tenold]

I've seen that before in the article and I think there's something that was lost in translation whether through misunderstood articulation or mistaken description.

 

The subject of "XX" number of layers has been a subject of rather elementary contention for many years. It's impossible to accurately assess the resultant *extant* layers in a finished billet, so the only way to assign a reletive value is to employ exponential calculation. The reality is that the basic raw material, in conjunction with the style of forging, the desired goal, and the skills and methods of the smith, determine the final result but even then it's moot to assign a qualitative value in terms of layer quantity. If the material was crap to begin with, then folding it 15 or 20 or 100 times will not change a sow's ear to a silk purse. If it was good material and the smith overheats and/or overfolds, then the material may very well be changed from good to bad. Each heating of the material results in a loss of carbon. Each folding results in a loss of material (and who knows how many of the previously created layers), so the billet gets smaller with each cycle. Only so much can be done to mitigate the carbon loss with each heating. So over folding also means over heating which in turn can be detrimental to the composition of the billet in terms of suitability for sword production. There is also some amount of layer drift as the hammer strikes the billet and layers "squish" and intermingle.

 

All in all, the way to look at the subject is that the material is folded enough times to meet the smith's desire and need for suitable sword material. The number of layers is interesting, but focusing on it somewhat pedantic.

[bluboxer]

100 folds = 2^100 power= 1.4 x 10^30 layers. 1.4 quintillion layers!

 

I think John C. has it right. Also; every forge heat represents a loss of carbon thereby reducing the as quenched hardness.

IMHO.

Ted beat me to it and a very good explanation at that.

[nagamaki - Franco]

The number of layers is interesting, but focusing on it somewhat pedantic.

 

Ah, a voice of reason

[Danocon]

I

All in all, the way to look at the subject is that the material is folded enough times to meet the smith's desire and need for suitable sword material. The number of layers is interesting, but focusing on it somewhat pedantic.

 

Hello all,

 

I have recently joined this forum. Mostly to get a better in depth understanding of traditional Nihonto. I have approached this from the bladesmithing side and have not really delved deeply into the nuances of older blades. Hence the reason I am here. So for the most part I will lurk here and absorb info. But in this discussion I may be able to add something.

 

Ted pretty much summed it up.

 

As received the Tamahagane is a very non-homogenizes porous material. The smith will select likely chunks, flatten them in the forge, heat them to CT (critical temperature) and quench them in water, then break them into little pieces. This helps him sort the low and high carbon pieces. The high carbon pieces can range from 1.5-2.0 percent carbon-way too much for a sword. You want .6-.7 percent.

 

The folding does two things-it refines and homogenizes the material exactly the way kneading bread dough gives it a finer texture and it reduces the carbon. Welding heat is right at the temperature where carbon begins to burn. In fact that is the sign that welding temperature has been reached. Little sparklers of carbon shoot out of the forge and there is a sound exactly like bacon frying.

 

You wan to hit it just as it starts to burn other wise you burn the steel into uselessness.

 

Looking at the theoretical number of layers

 

A 7 fold foundation forging gets you 128 layers. Combine three such billets and then fold them 6 more times theoretically you get around 24,000 layers.

 

In a .250" piece of steel each layer would be .0000104" thick. You would never see this. So the pattern we see is not each individual layer but amalgamations of layers.

 

Plus as Ted said there is huge amount of material loss. The smith tries to control the loss with rice straw and clay slurrys but even at that with a 13 fold process 50% of the material is lost.

 

In a 100 fold process all the material and certainly all the carbon would be gone long before the final fold.