Sword foldings

[plewis66]

I've just been playing with a little Java program, inspired by hearing things (not necessarily here) about swords being folded 'hundreds of times'.

I think the people don't realise that every time a sword is folded, the number of layers is doubled, and this very quickly leads to some stupendously large numbers.

It's certain that is someone says a sword is folded '500 times', they actually mean it has 500 layers. This means it is folded 10 times (giving 512 layers).

The very best swords might be folded 30 times, and this gives an incredible 1,073,741,824 (over 1 billion) layers.

The number of all atoms in the entire universe is something like 1,000,000,000,000,000,000,000,000,000,000,000,000, 000 (10 to the power 40).

If a sword really were folded 500 times, the layering would become meaningless. Each layer must be at least one atom thick (unless we get into nulcear folding - which I don't think even the best sword makers ever manged).

A sword folded 500 times would, if there were no physical limits, consist of this many layers:

327,339,060,789,614,200,000,000,000,000,000,000,00 0,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000,000,00 0,000,000,000,000,000,000,000,000,000,000,000,000!

[Khabbi]

Plewis66 ,Is your real name Stephen Hawking ?

[Neil Gendzwill]

The very best swords might be folded 30 times, and this gives an incredible 1,073,741,824 (over 1 billion) layers.

The steel was not normally (I'd say never but I'm not 100% sure) folded that much. Generally between 12-16 times. Also, the purpose was not to make layers but rather to make the steel homogeneous and to control the carbon content. If you're really curious, find a book called "Craft of the Japanese Sword" by Yoshihara and Kapp.

[ACRAWFORD]

10 folds would be 1024 layers.



2,4,8,16,32,64,128,256,512,1024

[plewis66]

10 folds would be 1024 layers.



2,4,8,16,32,64,128,256,512,1024

D'Oh! Schoolboy error!

[Raiza]

That's what happens when you use Java on a $2000 PC instead of a $20 calculator.

Which means those shinken folded to create "30 thousand layers" have been folded 15 times. Cool.

[roar]

Modern swordsmiths who has approached this "million and billion and zillion layers"-issue, has found that there is no point in folding the iron-lump more than 15 times, there is no measured overall improvement in the quality of the steel after that. But gimmicks sell, you now, and a myth is often preferred to reality.

[roar]

That's what happens when you use Java on a $2000 PC instead of a $20 calculator.

Which means those shinken folded to create "30 thousand layers" have been folded 15 times. Cool.

10 times 1024
11 2048
12 4096
13 8192
14 16384
15 32768

yes, I just had to check

[Takamatsu]

Hello I am deshi to a Tosho here in Japan I always laugh when someone say a sword is folded so many times depending on the quality of the tamahagane used a tosho can fold as many as 20 times after this you lose to much carbon and you cannot make good hamon everytime the block is heated it loses carbon. The main reason for folding is to take the impurities out of the tamahagane when tamahagane is made it is made in the old way only this can be used to make Japanese sword but many impurities are left from the charcoal and becuase the steel does not become molten all the way. when it is done it looks like crystals and a tosho can look at each piece and tell how much carbon is there. So we do sakite with a big ha,mmer while sensei moves the block and we do this 12 to 15 times until the grain and color is right if this is not done well you will have many kizu when the sword is polished.

[chidokan]

Takamatsu,
would I also be right in saying that every time you hammer you lose some mass of the steel as well... I guess you would start with, say, 2kg and finish with 1.2 kg of steel after forging? I am curious as to the actual starting weight and final weight of the average blade, as iaido people like me only see finished ones!

[Optomitrist]

Yeah, you are only trying to get the impurities out.

[Takamatsu]

Yes as you hammer and fold the hagane become more compressed impurities are lost from hagane and it becomes smaller and lighter I will measure next time I start a sword with sensei and let you know how much for sure. Since there are two types of steel welded together to make sword this kawagane and shingane i will check both and all when finished. Can you post picture of sword here and how ?

Takamatsu Kenshin

[neko kenshi]

N00bish question:

I had read somewhere that there is a core peice in the katana and then another layer of metal wrapped around this. Now it may be that I just terribly misunderstood or don't correctly recall the article I read, but if I am correct, Which part of the sword is folded, the core or the blinketing metal? I also heard that sand was folded into the steel to distribute carbon and that was the purpose of folding it, is this true? And if so, is this the only reason it is folded, or is folded steel actually much stronger? Sorry for questioning so much, and for sake of not bothering everybody with stupid questions too much in the future, does anybody know a good online in depth article about the making of a shinken they could refer me to? Thank you very much for any information you could provide me with, and sorry again for asking silly questions.

[Ric Flinn]

N00bish question:

I had read somewhere that there is a core peice in the katana and then another layer of metal wrapped around this. Now it may be that I just terribly misunderstood or don't correctly recall the article I read, but if I am correct, Which part of the sword is folded, the core or the blinketing metal?

Hopefully Takamatsu-san will correct me if I'm wrong, but I believe it's both the core and outer steels that are folded. The core steel isn't folded as much, however, and is a softer, lower-carbon piece of steel. Lower-carbon steel is more forgiving of shock and stress, but doesn't hold an sharp edge very well; high-carbon steel is more brittle but will stay sharp. Japanese swords combine these properties (with differing steel types and unique heat-treating) to make a more durable but sharper sword.

I also heard that sand was folded into the steel to distribute carbon and that was the purpose of folding it, is this true?

I don't think this is quite right; maybe what you're thinking of is that the steel used (tamahagane) comes from iron sand originally? But by the time a smith sees it it has been turned into solid chunks in a smelter (I have no idea what this process is called or how it works).

And if so, is this the only reason it is folded, or is folded steel actually much stronger?

Mainly to remove impurities and make the steel more uniform. Read Takamatsu-san's posts again. I guess this would make the steel stronger, though, since the steel will have less imperfections. The process of folding the steel came about simply because the swordsmiths only had impure steel to work with. If they had modern steels available, they may never have folded the steel at all. But they didn't, so they learned to use what they had, and I'm glad they did it this way. Even today, true Nihonto must be made from the same tamahagane steel.

Again, sorry if I have any information wrong or forgot any major details.

[Takamatsu]

Hello I am sorry for not responding for such long time I have been on a trip and now I am going Kyoto for one week. when I come back I want to start sword manufacture talking It is my favorite thing Ric san you are right I will fill in small details when I come back home. Ganbate!!!!!