Basic Japanese Sword Forging
Article by WarAngel.
Recently, I had the privilege of being able to attend a
five day class on Beginning Japanese Sword Forging, taught by Muh-Tsyr
Yee, and coordinated through the University of Guelph in Ontario,
Canada.
The class not only helped simplify basic blade forging but gave me a far
greater appreciation for the Japanese Sword ("Nihon-to"). I had no
prior forging experience, and my "eye" for the Nihon-to was very crude.
But the class ended up forging me than I was forging my two blades. I
finally regarded my blades. After hours of pounding the steel, the blades
seem to capture some of my life, sweat, and pain - and finally reflected
my joy of their completion, almost like newborns into the world.
This article is a most basic account - not so much of the class itself -
but a step-by-step process of how you - with a forge, anvil and perhaps
belt grinder - can transform a bar of steel into a fully functional
blade.
For the beginner, it is advisable to start on a tanto length knife
until you get the hang of the process.
1.
We start off with a bar of AISI 1050 steel, which is metallurgically
similar to traditional Japanese steel. It contains 0.50% carbon, and is
forgiving to the beginner, and great to work with. This bar is placed
into the fiery coals of the forge to heat up to that particular orange
glow. (The Japanese traditionally used tamahagane which is an iron
bearing sand. To create a sword from ore from tamahagane takes
much longer time, requires greater expertise, and exceeds the scope of
this article).
2.
The color illustrates the approximate temperature to heat the bar to in
order for it to be soft enough for hammering to shape. As it cools, it
turns to a cherry red and then back to gray. So hammer while hot!
Basically, start on one end of the steel bar and hammer to shape. One end
becomes the blade and the other becomes the tang.
If the forge is at the right temperature, the steel can reach the
appropriate temperature quickly, so don't walk away, because it's easy to
overheat the steel and cause it to burn. When it burns, the orange
turns yellow, and then the yellow can even go to white. When it starts
spitting bright sparks, parts of the steel are melting away and "eaten up"
by the heat. At that point, withdraw the bar/billet and assess the
damage. In some cases, the burnt part of the steel can be so coruscated
that you can hammer it right off!)
3. At this point, it was time to create the tip. Some anvils have chisel
attachments to do the job. Merely heat the steel to the proper forging
temperature and chisel the tip off. Illustrated here, the spine of the
blade is on the anvil and the edge is faced upwards. Note that the tip
angles towards the edge.
4. Now you hammer the tip down towards the spine. This allows the
grain to flow in that direction. Also, in traditional Japanese
sword-making, there are different methods of construction such as cored or
multi-plate methods. Had you cut the tip in the forward direction, then
the soft core metal will become the edge material at the point. (The core
is usually lower carbon, lower quality material and will not harden
sufficiently to hold an edge. Therefore, you have to bend/fold the point
backwards from the front so that you ensure that the hard jacket or edge
steel curves around to form the edge.)
5. It's starting to look like a blade, howbeit a crude one!
Anyways, keep working one side, keeping the blade straight. Hammer on
both sides of the blade to ensure your blade remains flat.
Japanese style blades (especially those of Western high manganese content
steels like AISI 1050 in this case) may be forged straight. The curve
will be produced by the clay coating and the heat treating process later.
(Traditional Japanese iron-bearing sand known as tamahagane was not
as responsive as modern factory steels, so a slight curve would have to be
forged in.)
After you're done with the blade side of your billet, forge the tang.
6. Okay, the blade is of sufficient length and the tang is forged. The
tang is supposed to be one third of the overall length. When it's reached
its approximate shape, excess steel can be ground down using a belt
grinder. I used a file on the spine to give it an upside-down "V" shape.
During the grinding process, the belt grinder put a lot of vertical lines
on the blade (from edge to spine). The filing put horizontal lines across
the length of the blade. This is to reduce the possibility of a crack
forming and taking advantage of the vertical grind lines. The blade is
heat treated thoroughly and then left to cool slowly over 8 hours in a
bucket of vermiculite. (I believe it derives its name from its
resemblence to vermecelli pasta or because it looks like worms - i.e.
"vermi".) It's insulation that looks like sawdust but it isn't, but a
great material to use for annealing.
7.
After the blade is fully annealed and is cool to the touch, we put a clay
coat. The coating we used was part red pottery clay, some sodium
hydroxide, and a bit of the shale (iron oxide) that comes off your steel
when you hammer it - plenty around the anvil in the forge. All ground
down and fine, with a bit of water, and then coated to your liking, about
1.5 to 2 milimeters. Notice the coating pattern. The clay is left to dry
(sometimes we had to encourage it over some flames). The sodium
hydroxide (lye) helps keep the clay flexible during the quench so that
it doesn't crack off during your heat treating. The iron oxide
(charcoal, sand, or whetstone powder will also do) helps maintain the
dimensions so the clay doens't shrink too much while drying. Some
smiths believe it increases thermal conductivity - if it does, it's
only negligible.
The trick is to not trap any air bubbles or allow any little
"caves" to form between the steel and the clay coat. And once
fully dried, it's
introduced into the fire of the forge until a very dull cherry red is
seen. You may need to turn off all the lights so as to get it to the
right temperature and color. Use a dark bucket if you have to. Just as
it's a very dull low red throughout the exposed part of the blade (not the
tang) then quench the blade in a trough.
At this point, if you feel a "ping" or "krok!" then the blade basically
didn't survive the quench - the edge might have cracked. This happened to
me, as I had got nervous, and when my instructor said, "Now!" I hesitated
and said, "Now?" This caused the blade to heat up more. The more drastic
the temperature change, the more the likelihood your blade would crack in
the quench.
8.
And here's the magic. The clay coat allows the blade edge and the coated
body to cool at different rates. The quick cooling of the edge allows a
formation of steel called martensite to form, which is harder. Softer
pearlite forms in the covered region. The blade, as a result, curves. I
had my blade crack near the tip. I had to saw it off, regrind a tip,
recoat the blade, re-heat it, etc. and the curvature was even more
pronounced.
9.
Scrape off the clay. The blade is essentially unpolished and looks a lot
worse than my picture (not to say my picture is all that great.) Find
something hard and scratch the blade a bit to test the hardness of the
edge and the softness of the body. My blade actually ended up being very
durable. I've poked a bunch of holes in some plywood and the edge still
holds very well.
10.
Polishing. The process of learning how to polish by a traditional
apprenticeship in Japan takes ten years to learn!
However, at a very basic level, you're
using Japanese stones and lots of water, and you start with lower grit and
you go higher. It's a painstaking process which was a pain in my back, so
I forged another blade instead!
And there you have it. Please pardon the brevity and the simplicity
of this. But the simplicity meant so much to me, as it meant that someone
as ordinary as myself could begin a journey of learning how to forge a
Japanese style sword in the future.
The University of Guelph, Ontario, Canada has an
extensions class in Basic Japanese Sword Forging, organized by Mr. Kim
Taylor (e-mail: ktaylor@aps.uoguelph.ca) (website:
http://www.uoguelph.ca/~kataylor/). The one I attended was taught by
Muh-Tsyr Yee. The class was conducted at Dean Piesner's forge - the Forge
and Anvil (http://www.forgeandanvil.com/). The Guelph School of
Japanese Sword Arts website is
(http://www.uoguelph.ca/~iaido/iai.gsjsa.htm)
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