Kind: captions
Language: en
this is a video about how Japanese
swords are made swords that are strong
enough and sharp enough to slice a
bullet in half the access we got for
this video is incredible we were able to
film everything from Gathering the iron
sand to smelting the iron forging the
sword to sharpening and polishing it
they even let us use it that is so
cool the method of making the swords has
remained virtually unchanged for
hundreds of years with everything done
by
hand they are still considered to be
among the best in the world the Japanese
made a weapon that was the absolute
Pinnacle for their style of warfare and
the materials they had at hand these
swords are held in such high regard that
one from the 16th century has been
appraised at $105
million making it the most expensive of
sword ever
built in the shiman province of Japan
there is a smelter that is lit for only
one night each year where steel is made
in the same way it was 1300 years
ago it's known as the tatara method and
only steel made in this way ends up in
the very best Japanese swords
and we were invited to come film
it just after 9:00 a.m. the ceremonial
prayers are said and the fire is lit by
a Shinto
priest everyone that will be working the
smelter will be here for at least the
next 24 hours that includes veritasium
producer Peter I'm committed we're going
to do this it's going to be
fun sword making in Japan goes back
about 3,000 years but in those days
swords were made out of bronze we're not
sure how people first learned to smelt
metal but it was likely related to
Pottery in that you were using these
Rocky ores to make glazes and such for
pottery under very controlled
atmospheres and then find maybe The
Potters found metallic beads in the
bottom of the furnaces that they were
firing it this possibly gave them the
idea bronze was discovered before Steel
because it's an alloy of copper and
usually tin both Metals with low enough
melting points that they can be smelted
in regular Pottery kils the problem with
bronze is that although it can be
sharpened it's too soft to hold an edge
for long so Japanese sword makers
shifted to Steel 12200 years ago in the
hon period this is what most people
would recognize as a Japanese sword it's
made of steel with a curved blade
steel is an alloy of iron the fourth
most common element in Earth's crust the
oceans of the world used to be rich with
dissolved iron but 2 and A2 billion
years ago cyanobacteria started
photosynthesizing and creating oxygen
the iron reacted with that oxygen
precipitating out of solution to be
deposited at the bottom of the ocean
incidentally the cyanobacteria were
poisoned by the oxygen that they
themselves eles produced so it's thought
that when levels got high enough they
died off and as a result oxygen levels
dropped and iron no longer precipitated
out of solution then the cyanobacteria
could multiply again and the cycle
repeated that's why most of the world's
iron is found in layers of sedimentary
rock called banded iron
formations each layer of iron was formed
during a global flourishing of
cyanobacteria that infused the ocean
with oxygen the majority of the global
iron Supply comes from these banded iron
formations because of their High
concentration of iron up to around 60%
iron oxide by
weight but Japan with its mostly
volcanic geology has barely any of these
sedimentary iron oxides and this is
likely why the country was late to the
steel production game archaeologists
have found steel artifacts in Anatolia
which is modern day turkey that are
nearly 4,000 years old but in Japan
Metals including steel were imported
from China and Korea up until the 8th
century when Japan started making its
own steel so where did they get the raw
[Music]
ingredients well ous rocks like granite
and diorite still contain iron oxides
just in much lower
concentrations but as the mountains are
weathered these iron oxides are broken
apart and washed Downstream eventually
they become part of the
sand the Japanese noticed that because
iron oxides are denser than other
minerals in the sand they accumulate in
places where the river changes direction
or speed the heavier iron sinks to the
bottom and the lighter material is
washed
away to amplify this effect they
deliberately created diversions in the
river to increase the concentration of
iron what you do is you Dam off a
section of river and then you drag sand
into it because iron is heavier than the
other parts of the sand it is the thing
that gets left behind and everything
else gets washed
Downstream with this method you can get
iron Sands with 80% iron oxides by
weight that's more concentrated than
highquality iron
ore and since it has fewer impurities
it's an excellent source material for
high quality Steel
if you heat up those iron oxides to over
1250° C you can break the bonds with
oxygen and get pure iron but pure iron
is actually softer than bronze so in its
Elemental state iron provides no
Advantage but nature gave humans a lucky
break one of the few ways you can heat
something up to
1250° is with charcoal and charcoal is
basically pure carbon and if you add
just a little bit of carbon to iron it
creates an incredibly strong alloy steel
yeah a lot of people see it as a heat
process I I see it as a chemical process
Alloys are usually stronger than pure
metals because they contain different
sized atoms and this reduces the ability
of atoms to slide past each other when
an external force is
applied so I've just been given gloves
other gloves and a towel so things are
very much uh getting real I'm genuinely
quite
worried and here is the room with all of
the charcoal that we're going to be
using overnight there's just bags and
bags of this stuff
[Music]
there's a Buddha
saying before Enlightenment chop wood
carry water after Enlightenment chop
wood carry
water I'm here
okay so we're lining up on the four four
corners I
guess W oh boy didn't do a great job of
that
so the rain is coming so we're quickly
getting all of the charcoal out and then
measuring it so each bag of these is 10
kilos
okay so with the iron sand it is mixed
together with water because if you don't
mix it with water and you put it on the
plant it just flies straight
up but if you mix it with too much water
then there is water that's going to heat
up it's going to become water vapor and
the whole kill could explode
terrifyingly enough they do this by feel
they mix in enough water until the iron
sand is clumpy but again if it's too
much the whole thing could
explode co co
hi okay put some iron in
it is just past 4 in the afternoon and
over the last couple of hours we have
added 250 kg of charcoal and nearly 60
kg of iron sand so yeah it's a slow
process but I think think we're starting
to get somewhere I have no idea because
obviously the thing is
hidden but it should be
growing to achieve the high temperatures
required to make steel you need a strong
steady supply of oxygen for hundreds of
years this was provided by huge foot
operated Bellows it would have taken an
aroundthe clock full body effort by many
men to maintain the furnaces temperature
when I came here I was a little bit sad
that the Bellows were electric I really
wanted to you know have this proper
experience have this proper workout of
stepping on these Bellows for 24
[Music]
hours the temperature inside the smelter
gets up to, 1500° C just below the
melting point of iron which is 1538 C so
the iron being smelted isn't liquid but
it's soft and malleable enough to Clump
together into a big block of iron no
matter how high quality the iron sand is
there will always be some impurities
like sulfur phosphorus and silicon
oxides they combine with carbon from the
charcoal and melt at a lower temperature
than iron so they they become liquid and
flow to the bottom this is known as
slag after many more hours of adding
charcoal and iron sand it is time for
the first removal of the
slag before the first removal of slag
another prayer is
said oh that's insane
W so for the last 3 hours there's been
three processes that we've been doing
one is adding the charcoal two is adding
the iron sand and three is opening up
the smelter from the bottom to break
apart the impurities so they can flow
out just want you guys to know that it's
3:16 in the morning and I'm still here
and I'm really
[Music]
sleepy so it's currently 6:00 in the
morning the next day we've been smelting
for 21 hours I'm exhausted but the sun
is about to come out and it's been
pretty amazing I got to be honest we got
to close these doors really quick before
they get mad at
me at 9:00 a.m. the next morning the
smelting is complete a total of 614 kg
of iron sand and 67 20 kg of charcoal
were added to the
smelter at this point in a traditional
smelter the only way to get the steel
out would be to break it
apart these days a crane is used to take
the smelter apart oh wow okay
oh and what is left to show for all that
hard work is a 100 kg block of steel
iron and slag only around a third of
this block is high enough quality to be
used in Sword
making oh that's insane that's so cool
there result old for old uh hard
[Music]
work this is step one of making a
Japanese
sword the steel is sorted by quality and
carbon content which is also done by I
in fact this is one of the exams you
need to pass to be certified as a
swordsmith then the different grades of
Steel are sent out to one of 300
swordsmiths around the country only 30
do it as their full-time job and one of
them is akahira kokaji who we went to
visit next this is when the forging of
the sword begins in a coal oven with
hand pumped Bellows the steel is heated
until it is soft and
malleable then using hammers the master
swordsmith flattens out the steel
in the old days this would have been
done by the swordsmith and three
apprentices the swordsmith using a
smaller Hammer would set the Rhythm and
the apprentices would use big mallets to
flatten the
[Music]
steel that was H
terrifying these days electric hammers
are used
[Music]
when the steel is flat
enough it is then bent back on
itself and it is then hammered again to
press the steel back together into a
solid
[Music]
block so why go to all this effort flat
in the steel only to fold it back on
itself and end up with a chunk of Steel
the same size as
before well because folding does two
very important things first it spreads
out the impurities like Silicon sulfur
and phosphorus it spreads them out
throughout the steel this ensures a
uniform consistency without any weak
points second it gives the steel a grain
after folding the sword it is now
reinforced in the direction that it will
be hit in in combat and as a bonus the
steel is exposed to the air so there is
a small amount of oxidation creating a
darker colored steel which when folded
makes beautiful
patterns there are some swords which
have more than a billion layers now this
doesn't mean the sword has been folded a
billion times since every fold doubles
the number of layers so you only need
about 30 folds to get a billion
layers but usually a sword is folded 10
to 13 times resulting in a few thousand
layers of
Steel now a blade isn't made from a
single block of steel the carbon content
affects how hard the steel is so
different carbon percentages are used in
different parts of the
blade because carbon atoms are much
smaller than iron atoms they can fit
inside the crystal lattice of iron these
trapped carbon atoms then apply an
outward Force to the lattice putting the
steel under stress the higher the carbon
percentage the harder and more rigid the
steel but this hardness comes at a cost
the steel becomes brittle making it more
likely to Chip and shatter rather than
bend so what swordsmiths do is they use
steel with different carbon contents for
different parts of the blade The Edge is
always high carbon steel to make it hard
and rigid so it can maintain a sharp
edge for a long time but the spine is is
usually made of lower carbon steel which
allows the sword to flex without
breaking this is done by welding
together pieces of Steel with different
carbon
contents so uh we have about a 15minute
break because you know it takes a while
for the iron to heat up and then melt
together and then we're back in there
it's very hot it's very very hot in
there it's kind of unbelievable that he
can do this for 4 hours at a time after
after the sword is hammered into shape
which is a straight blade it is covered
in a layer of clay a thick layer for the
spine and a thin layer for the blade
itself it's then heated in the furnace
and then rapidly cooled in water a
process known as quenching now because
the layers of clay have different
thicknesses the rate of cooling is
faster for the edge than the
spine when the steel is heated carbon
enters the iron lattice and since the
spine of the sword is covered in thick
clay it will cool slowly giving time for
the carbon atoms to leave the iron
Matrix this will lead to a very low
carbon steel called ferite but the
carbon atoms which have left the Matrix
will be caught by other iron atoms and
create a type of Steel known as
cementite the combination of ferite and
cementite is known as perlite and it's a
mostly soft and ductile form of Steel
though parts of it are hard due to the
cementite so perlite forms the spine of
the sword in contrast the very thin
layer of Clay on the blade means that it
cools very rapidly so more of the carbon
is trapped in the lattice this forces
the lattice structure to change from
cubic to tetragonal making a form of
Steel known as Martin site since the
trapped carbon puts stress on the
lattice Martin site is incredibly hard
exactly what you'd want for the edge of
a sword
the tetragonal lattice structure of
Martin site also takes up more space so
the edge of the blade expands relative
to the spine curving the sword backwards
the iconic curve of a samurai sword
comes from the formation of
Marite you can actually see the boundary
between different types of Steel in a
finished sword by the difference in
color this is known as hamon which
literally means Edge pattern
at the Victoria Albert Museum in London
there is a Japanese sword that has a
very detailed little dragon in the hone
and I've looked at it many times I don't
okay I don't know how he did
that about onethird of all blades
shatter during the quenching process you
quench it once and you thank the stars
that you made it the sword is then
placed back in the forage to evaporate
any remaining water this also provides a
little bit of energy to loosen some of
the Crystal structures making the sword
less brittle and that's about the extent
of the tempering process on a Japanese
sword which that that might be enough to
relax things a bit but they kept the
edge much harder than you would have in
the
West after the sword is forged it is
sent to a polisher the polishing and
sharpening of a sword is also done by
hand with wet stones of different
coarseness it can take a month to
sharpen and polish a single sword
one of the things that I love is that
like the this table is sloping down and
the entire floor over there is sloping
down so when you like add add the water
all of the residue and all the water you
know flows downhill so it's not
perfectly
flat sometimes the swords are also
engraved with beautiful patterns though
this is quite
[Music]
rare and after all that the sword is
done
to learn how to use a Japanese sword
Peter got a lesson from a master Takara
takanashi he is the 10th Generation
student of mamoto Musashi a legendary
Samurai Musashi killed his first
opponent in single combat at the age of
13 he spent the rest of his life
perfecting his sword fighting inventing
a new technique with two swords Musashi
fought in more than 60 duel to the death
and he won every last one of
them there is a story about a duel that
took place during a snowstorm as he
faced his opponent Katana outstretched
Musashi was so calm and kept his sword
so still that snowflakes began to
accumulate on the thin edge of the
blade so during the lesson I thought I
would get to use a katana but instead we
spent the entire time learning how to
take the blade out of its sheath and
then put it back
in so when I actually got the chance to
use a katana to slice through some
things I was deeply
unprepared well looks like it's your
turn so
scary okay so this has been an amazing
day we've uh looked at some beautiful
katas and now these wonderful people are
letting me use one of their just
unbelievably beautiful pieces of art to
chop some
[Applause]
things like this is kind of the best day
ever there really is something
remarkable about Japanese swords the
amount of care attention and expertise
that each step requires from the
Gathering and refining of the iron sand
to the smelting to the forging and
sharpening a sword each step takes so
much time and skill it's incredible that
all these things were discovered by
trial and error to produce artifacts of
such high quality that they are still
prized centuries
later before I made this video I didn't
really appreciate that swords can be art
to me it's a good reminder that whatever
you do you should do it with deep care
attention to detail and love for the
craft do that enough times and you might
just make something
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