The art of forginational Geographi

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12-10-2006, 09:26 AM
Bruno

The art of forginational Geographi

Edit: thread title accidentally messed up. Seems I cannot correct this anymore.

Yesterday evening (while lapping my stone) I was watching a brilliant documentary on National Geographic about the forging process of a katana.
They rerun the documentary on wednesday at 15:00 CET.

Some interesting tidbits:

There is 1 place in Japan where they smelt the iron for katana. they use a very pure iron sand that is found locally. the smelting process takes 3 days and nights. during that time, the smelt master (who is 70 years old) continuously monitors the oven without sleeping.

Little lumps of steel are selected by the smith, and hammered into larger pieces. These large pieces are hammered and folded several times. Then iron and hard steel are hammered together and flattened to form the sword shape.
One thing I did not know is that until it is quenched, the sword is as straight as an arrow. Before heating it, it is covered with thin layers of clay and mud. of varying thickness
When the sword is quenched, the edge cools quickly because it is thin, and has only a thin coating of clay. the spine cools slowly, due to it being thicker and having a thicker coating.
The asymmetric cooling causes the sword to bend. It is this process that creates the curvature of the katana.
If the sword is not perfectly left-right symmetrical before quenching, or if there is a n uneven clay coating, the sword also bends to the left or right, and it has to be thrown away. 3 months of work down the drain.

The sword is polished and sharpened by a sword polisher. He has a large collection of stones that can cost thousands of dollars each. Polishing and engraving takes another 3 months.

The end result is a sword that can cost up to 50000$ or more if it was made by a famous smith and polished by a master polisher.

You really have to watch that documentary if you can. it is worth it.
12-10-2006, 10:56 AM
ToxIk

Very cool. I don't get national geographic stuff around here. Well, I might, but I never see it in the tv guide. I hope this one gets posted on the net somewhere just like the shaving one from a bit ago.

I've always had a fascination with japanese katanas. The amount of craftsmanship and meticulous precision that goes into one is astounding. It's like an orgy of razor porn :p

It's almost strange how the inherent curvature of the sword adds a certain elegance to them as well. Very clever that they'd manage to differentially temper the blade such that the spine in soft while the edge is hard. Gets you some of the best of both worlds in there :)
12-10-2006, 02:08 PM
Mike Blue

Only a few tidbits to add:

Quote:

Originally Posted by Bruno

...National Geographic about the forging process of a katana....clipped...There is 1 place in Japan where they smelt the iron for katana. they use a very pure iron sand that is found locally. the smelting process takes 3 days and nights. during that time, the smelt master (who is 70 years old) continuously monitors the oven without sleeping.

That'd be Shimane and a man named Kihara. It's fascinating to watch him work. He's been to the University of Minnesota and hopefully they will get him back sometime soon. The fact that their poor material produces 2.5 tons of sword grade steel is even more fascinating.

Quote:

...hammered into larger pieces. These large pieces are hammered and folded several times. Then iron and hard steel are hammered together and flattened to form the sword shape.

It's not a simple mechanical joint. It's a high temperature weld. Otherwise the layers would all come undone.

Quote:

If the sword is not perfectly left-right symmetrical before quenching, or if there is a n uneven clay coating, the sword also bends to the left or right, and it has to be thrown away. 3 months of work down the drain.

Realistically, after all that, plus the price of the original material, it'll be hammered back to straight again. If that fails or the blade breaks, it will become the little chunks that become the next big blade. Nothing is thrown away.

If the hamon is wrong because the clay popped incorrectly (in the second and a half that takes to happen), they'll recoat it and try again.

Keen observations though. Everyone should watch programs like this, so the understanding of how steel used to be made sinks in. It makes us all better educated buyers and users of that thin little strip in our hands.
12-10-2006, 02:11 PM
Mike Blue

Quote:

Originally Posted by ToxIk

...Very clever that they'd manage to differentially temper the blade such that the spine in soft while the edge is hard. Gets you some of the best of both worlds in there :)

Yes it does. What's more interesting is that the steel maker produces a product that is designed to be low hardenability. That means that given the thickness of the blade, only a smallish portion of the blade at the edge has the potential to harden if the circumstances are correct. The back of the blade will not harden because it's too thick. The control over this process is not just the clay or the temperature but also intimate knowledge of the material and how it will behave.

As long as there is no "dreaded ping" during the shock of the water, it'll be a good blade.

Fascinating stuff...
12-10-2006, 06:52 PM
Kees

Quote:

Originally Posted by ToxIk

Very cool. I don't get national geographic stuff around here. Well, I might, but I never see it in the tv guide. I hope this one gets posted on the net somewhere just like the shaving one from a bit ago.

Try this link for listings: http://channel.nationalgeographic.com/channel/