Secrets of the Samurai Sword

PBS Airdate: October 9, 2007

NARRATOR: The samurai were the heroes of ancient Japan. Still, today, their legend continues. The samurai's sword is one of the greatest fighting weapons of all time, perfectly engineered for close-up combat, renowned for its deadly cutting edge.

Modern science can now reveal the technical excellence of this ancient craft.

MICHAEL NOTIS (Materials Scientist, Lehigh University): It's certainly an object of absolute beauty, from both an aesthetic and a scientific point of view.

NARRATOR: But can it explain the mystery of how these swords were made?

STEPHEN TURNBULL (University of Leeds): The great swordsmiths of Japan were steeped in the mysterious traditions of the metal. They were able to transform this mystery into something that was very, very real: the samurai sword.

NARRATOR: It is said that the sword is the soul of the samurai. Can modern science uncover its secrets? Coming up on NOVA, the Secrets of the Samurai Sword .

NARRATOR: By day, Midori Tanaka is just another face in the crowd on the busy streets of modern Japan, working as a mild-mannered receptionist for a midsized electronics company. By night, however, she is anything but mild mannered.

Midori is an expert swordswoman, descendent of a long line of samurai warriors.

The samurai were noble warriors of medieval Japan, similar to the knights and noblemen of Europe. During this 600-year era, beginning in the 12th century, Japan was ruled by regional warlords. The samurai were part army, part aristocracy, and, at times, freelance mercenaries. They lived by a strict code of honor that demanded rigid discipline and unfailing loyalty. Their sword is one of the greatest fighting weapons of its day, if not of all time. It could cut a man in half with a single stroke.

Today's swordsmen and -women test their mettle on bamboo and rolled straw: not easy to cut with just any knife, and similar, it is said, to the toughness of cutting through human bone. The sharpness and strength of the sword is legendary.

Legends are one thing, but how does the quality of the samurai sword stand up to the test of time?

Mike Notis, a samurai sword expert, is a professor at Lehigh University, a leading materials engineering school that has an important history with the once-great American steel industry.

MICHAEL NOTIS: If you look at the blade itself and you look at the surface appearance, you see one level of beauty. But with the instruments that we have available, we can go to different structural levels, and we can see the care and the fabrication capability that these craftsmen had to make an object of absolute beauty, from both an aesthetic and a scientific point of view.

NARRATOR: This remarkable weapon reveals a highly developed metal-making skill that dates back more than a thousand years, to 900 A.D. The electron microscope can now reveal the quality of this ancient steel, as well as some of the secrets of its skillful engineering.

MICHAEL NOTIS: And this is the boundary.

NARRATOR: Embedded deep into the material of the blade are different types of steel, each contributing to the sword's deadly effectiveness and its unique design.

MICHAEL NOTIS: There are two types of blade weaponry. One is a piercing instrument, an epee, or a fencing foil, for example. The other is the saber or the Japanese sword, where you slash. You use your whole body force, your upper body, in order to apply the largest force you can. The unique aspect of the Japanese sword is that the craftsmen were able to put the right materials in the right place to get optimum properties for the entire object.

NARRATOR: In our common understanding, we think of all metals as strong. But in fact strong metals have other important characteristics. Controlling these characteristics requires expert formulation. So how, in the absence of understanding this science, were the ancient craftsmen of Japan able to achieve such technical excellence?

In the small village of Shimane, in southwest Japan, they still make the metal ore for samurai swords the same way it has been done for centuries, in earthen smelting furnaces called tataras.

Akira Kihara is one of the last remaining tatara masters in the world. He won't sleep for three days and three nights as he watches the furnace create steel that is the quality needed for the world's sharpest swords.

This special steel called tamahagane is made from iron ore sand, collected in local rivers, and charcoal.

AKIRA KIHARA (Tatara Master): Within an hour, the iron sand sinks to the bottom, to what we call the bed of fire. When we look at the bed of fire we can clearly see, from the color, whether or not it has become tamahagane.

NARRATOR: The traditional Japanese smelting furnace is constructed out of clay with a row of inlets along the sides. Air is blown into the furnace with bellows that drive the temperature up to nearly 2,500 degrees Fahrenheit. Think of this as a very hot oven, because at this stage, making steel is a lot like cooking.

RICHARD P. VINCI (Materials Scientist, Lehigh University): Steel is basically iron, and to that you add a little bit of carbon, and the carbon gives it much more strength than the iron would have by itself.

NARRATOR: Rick Vinci, a professor of material science at Lehigh University, says that just like in cooking, the ingredients of the metal can make all the difference.

RICHARD VINCI: It is a little bit like being in the kitchen and adjusting a recipe by adding a pinch of salt, or maybe you say, "Oh, boy, this could really use just a hint of lemon," and somehow that little bit really changes the food. In the same way, some of these subtle chemistry changes can really make important adjustments to the overall properties of the metal.

NARRATOR: By the end of the second day, the furnace has already eaten up 18 tons of iron ore, sand and charcoal—the fire's fuel and also the source of its carbon.

MICHAEL NOTIS: Steel is composed of the element iron and the element carbon. The ancient Japanese could physically see iron, but they had no idea what carbon was. They understood that charcoal was needed for the process, but they didn't understand charcoal as carbon. Carbon wasn't discovered as an element until just a few hundred years ago.

NARRATOR: Today the recipe is no secret. The hard part is keeping the oven cooking just right. Throughout this smelting process, Kihara must tend to the furnace to make sure that nothing goes wrong.

AKIRA KIHARA: The furnace is like a human being. We can think of the iron and coal as food we feed her. She digests it so that she will bear good tamahagane.

NARRATOR: Inside the furnace, the iron and carbon are slowly forming into the right mixture. Beneath the furnace, lies a chamber nearly 10 feet deep. Ventilation channels flank either side. Any moisture seeping in from the ground would lower the temperature, ruining the steel, and they would have to start all over again.

In the very hot center of the furnace, the iron and carbon combine. This process happens at the atomic level. By nature, iron atoms bond to one another in a specific geometric arrangement. When heated, that structure changes form.

RICHARD VINCI: Iron actually has two different forms that it takes: a low temperature form, in which the atoms are arranged in a particular way, and a high temperature form, in which they are arranged a little bit differently. There's actually more space between the iron atoms at high temperature.

NARRATOR: But when this high temperature form cools quickly, it contracts, and the carbon atoms become trapped in between the iron atoms.

RICHARD VINCI: If it does that, the iron can't fully assume the structure that it would like to. It will be distorted by virtue of the fact that the carbon atoms are lodged into these spaces that are really too small for them to fit into. And that kind of form of steel—iron and carbon mixed together—is very, very hard, very, very strong.

NARRATOR: Manipulating this heating and cooling process, as well as controlling the ingredients in the steel, allows metallurgists or ancient craftsmen to change the properties of the metal.

RICHARD VINCI: Metals are elements, so they are made up from single kinds of atoms. Most of the elements on the periodic table, it turns out, actually are metals, even though we don't think of them as metals. We usually think of metals as being solids; they are shiny, they conduct electricity and heat really well. And perhaps more importantly for a lot of their uses, they have this ability to bend, to take on new forms and also to have their mechanical properties be controllable. And so by adjusting their chemistry and adding a little bit to them or taking something away, by controlling their heat treatment, you have a lot of control over their properties, and this makes them very, very versatile and, really, the underpinnings for the modern society that we live in.

NARRATOR: Modern like the skyscrapers on the busy streets of Japan. These towers of steel have their roots in the ancient metal-craft of the sword.

In the traditional smelting process, the metal ore never completely reaches a liquid state so that the steel ore, or tamahagane, will not be uniform in its mixture of iron and carbon. Some parts will have more carbon, some less. These different mixtures of steel will become very important in the engineering of the sword.

More carbon makes the steel harder so that it can hold a sharper edge, but too much carbon makes the steel brittle, and no samurai wants to be caught with a broken sword.

In engineering, there is a limit to how hard you can make the metal before it becomes brittle. The standard test for measuring this is called the Charpy test. Here, a large pendulum is used to break a sample of metal. Hard metals don't bend, so they break more easily. A metal that resists the energy or force of the pendulum and bends before it breaks is said to be tough.

RICHARD VINCI: In the case of tough metal, instead of just breaking, it actually bends. And, so, what you'll see is a lot of stretching on one side of the metal until, eventually, it's been torn apart. It actually looks a fair amount like if you take a piece of taffy or a Tootsie Roll—and as you know the Tootsie Roll or the taffy will stretch first and then it will come apart—and you will see the effect of that stretching. You want very large energy absorption to have a tough metal. You want it to be able to take a lot of damage before it breaks.

NARRATOR: At Lehigh University, these basic principles of toughness and hardness are put to the test, literally. The ATLSS Center is one of the largest metal testing facilities in the United States. Here they can test huge metal structures to see how they will stand up in the real world.

RICHARD VINCI: Every time a building is built, all of the steel that goes into that building must be qualified before it can be used in the structure. And some of those tests include hardness and toughness measurements.

NARRATOR: Steel beams from skyscrapers and bridges are trucked here to be put through punishing tests that simulate major earthquakes or a hundred years of heavy truck traffic.

ALAN W. PENSE: It is quite a bit of motion, though. I don't know, getting a structure to survive with that kind of motion is, I think, very, very impressive.

RICHARD SAUSE: Collapse prevention: that is what we are after.

ALAN W. PENSE: Collapse prevention, right. See how it's deforming and bending but not cracking?

NARRATOR: The test is recorded in time-lapse footage that shows these structures pushed to the breaking point. Engineering metals, whether in a sword or on a super highway, is about making sure they are tough enough to last.

ALAN W. PENSE: And this whole test took how long?

RICHARD SAUSE: This test took a whole day. It simulates 30 seconds of earthquake.

NARRATOR: At the back of the ATLSS center is an area they call the graveyard. Here is the final resting place of structures that weren't tough enough to stand the test of time.

Working with metals has always been dangerous. Back at the smelting furnace, there is a Shinto shrine devoted to a sacred deity the workers believe helps keep them safe. These elaborate rituals are not just about safety, but, as Mike Notis explains, they are also about quality control.

MICHAEL NOTIS: In modern industry, today, we depend very strongly on quality control. The ancient Japanese swordsmiths used religious ritual as their process control to make sure that each and every time that they manufactured this same object, it was done exactly the same way. They didn't have science to do it, they had religious ritual.

KENNETH KRAFT (Buddhist Studies, Lehigh University): If you think that what you are doing has religious significance, you pay extra attention to it.

NARRATOR: Ken Kraft, a professor of religion and an expert on medieval Japan, says this reverence helps explain why the sword is so important in Japanese culture.

KENNETH KRAFT: They'd say that the sword is the soul of the samurai. In almost all pre-modern cultures, matter and spirit were interfused, and so it wasn't so hard from theâ¦to imagine that an object could have this kind of power—what's called the luminous power or an otherworldly power. And in Japan, the gods could be found in any natural object, including waterfalls or trees or a mountain. So it wasn't a big leap for them to think that an object as powerful and as beautifully made and as reverently made as a sword could have some sacredness to it.

NARRATOR: It is that sense of the sacred that drives Master Kihara. After 36 hours of feeding the voracious fire, everyone is exhausted, but Kihara carries on, never sleeping, always keeping vigil.

In ancient Japan, sword makers and the weapons they helped to produce were vital to the noblemen and the samurai. They were the military-industrial complex of their day, which helps explain why their metal techniques became so advanced.

KENNETH KRAFT: Around the whole world, in 1700, the Japanese were the masters of this particular technology that produced swords. So we have to remember we're dealing with a culture in which the military dominated for 4- or 500 years. That gave them a lot of time to perfect whatever military implements they wanted.

NARRATOR: Using only the ancient methods, Kihara monitors the process by watching and listening to the fire. On the morning of the fourth day Kihara can tell by looking and listening inside the core of the tatara that it is time to break up the furnace and extract the steel ore.

AKIRA KIHARA: I could see the core. It looks good. That's a big relief. I'm happy.

NARRATOR: Happy, yes, but no one can afford to relax yet. Until they get the steel out, there's no way of knowing if it's samurai-sword grade or only good enough for kitchen knives.

Once the ingot is cooled, it will be broken into small pieces. This process helps to sort the steel. Pieces that break off easily are more brittle. Parts that are more difficult to break apart are tougher. The most skilled masters are those that can deliver the best quality of both types.

AKIRA KIHARA: It's like when your child is born, it was worth waiting for. I am very happy.

NARRATOR: Kihara will then choose which of these pieces is good enough to go to the sword maker, who will give this raw steel its famous shape.

While craftsmen like these keep the tradition of sword-making alive, the legend of the samurai also lives on in the popular imagination. The samurai are to the Japanese culture what cowboys are to America, heroes of a lost era. Surprisingly, samurai movies had a big impact on the American Western itself.

Akira Kurosawa's famous film, Seven Samurai was turned into the classic western The Magnificent Seven . The stories are nearly identical. Seven brave warriors rescue a poor village from bandits. The heroes are reluctant to use their weapons, but expert at it. Both of the leading men are bald: Takashi Shimura and, famously, Yul Brynner. There is one big difference: in the American version, the sword was replaced by the classic six-shooter. Both, however, do the trick.

VOICEOVER ( A Fistful of Dollars ): The man with no name. Danger fits him like a tight black glove.

NARRATOR: Another Japanese classic, Yojimbo, became A Fistful of Dollars which launched Clint Eastwood's movie career. Even Tom Cruise tried his hand, as the improbable Last Samurai .

All of these movies show that sword fighting, like the gun battles in westerns, makes for good cinematic action. One samurai film buff calls it "sword porn." To create the perfect fighting sword, or prop, form and function were engineered together. The laws of physics dictate the sword's unique curved shape.

RICHARD VINCI: With the curve of the blade, if you are doing that slashing motion, it actually makes it possible to move the blade in an arc, which is what you want to do when you slash something. If you have a straight blade and you attempt to slash, at some point you have to slash and then pull, because the blade is straight.

NARRATOR: To create its unique shape, the raw steel must be forged into the fighting blade. And while the work of a blacksmith seems pretty straightforward—brute strength that muscles metal into shape—the real secret is what is going on deep inside the metal.

Sakurai is a small town, not far from the fabled city of Kyoto and home to Gassan Sadatoshi, one of Japan's most renowned swordsmiths. His family has been in the business for generations.

The pieces of raw steel arrive from the smelters. Together with his son and assistant, Gassan carefully examines the tamahagane to see if it is up to scratch for his next sword.

Gassan can judge from the texture and color of the raw steel just how much carbon is in it. Brighter pieces have more carbon.

STEPHEN TURNBULL: The great swordsmiths of Japan were far more than just blacksmiths. They weren't just people who bashed metal into a sword shape, they were more like alchemists.

NARRATOR: Historian Stephen Turnbull, from the University of Leeds, is a renowned expert on the samurai sword.

STEPHEN TURNBULL: They were steeped in the mysterious traditions of the metal: how it was melted, how it was molded, how it was beaten. They may not have understood the chemical composition of it, but from years of practice, years of apprenticeship, and years of tradition, passed on from master to pupil, they were able to transform this mystery into something that was very, very real, the samurai sword.

NARRATOR: Remember how, at the smelter's furnace, some of the metal was of a different atomic composition that made it either harder or tougher? Gassan needs to find the best quality pieces of both types, because part of his art is to find a way to combine them so that the sword will have the advantages of their different characteristics.

There is really still only one way to learn the art of sword making, through apprenticeship—no easy career path. They rise at dawn, help with household chores, and work with their master six days a week. It takes years to learn correct forging technique.

The untreated metal is protected from rusting before the process begins. Heating softens the steel for hammering so that the pieces can be formed into one. The hammering also drives out most of the remaining impurities, called slag. Molten slag can be seen in some of the dramatic sparks as it is squeezed out of the steel by the hammering.

The steel is pounded flat and then folded time and time again to thoroughly mix the iron and carbon. Gassan gauges the concentration of the carbon by the way the steel bends.

How good a job did the ancient blacksmiths do? With modern tools we can see. Using a special electron microscope, trace amounts of unwanted elements like sulphur or phosphorus that would weaken the steel can be detected.

MICHAEL NOTIS: And what you see on the right side is the x-ray spectra collected from that area, which shows only the presence of iron, which is the high peak, and carbon all the way to the left, which is the low peak. We can tell this is a very high quality steel. It's got only iron and carbon present in it.

NARRATOR: Another thing that is happening in this brutal pounding of the steel is that the shape of the metal, all the way down to the atomic level, is changing.

RICHARD VINCI: The material is actually getting harder as it's hammered. Many people have the experience of bending something and feeling it get harder. A great example is if you're trying to run copper tubing, installing an icemaker or doing something like that.

Initially, when you get the tube in a coil, like this, it's relatively easy to change its shape. You can straighten it, make it go around corners, whatever you like to do. But if I make a mistake and try to change the shape of it at this point, once it's already been straightened, it gets much more difficult the second time, and even more difficult the third time, to straighten it out again. Because every time I bend it, I create lots of microscopic defects inside, and the more defects I have, the stronger the material gets.

Now, the smith, ultimately, would like to keep changing the shape of the sword, and so this hardening is not really what he wants. So he can put that sword back in the flame, heat it up, and the heat will heal the defects. At that point the material will go back to being relatively soft and formable, and the cycle can be repeated over and over again.

NARRATOR: These defects also play a key role in giving metals one of their unique characteristics, their bendability. As Vinci explains, this bending happens at the atomic level.

RICHARD VINCI: Metals have this capability in which, when you apply a stress, the atoms can move, and they can swap locations within their general arrangement. They don't mind being in this position or this position or this position. And for that matter, when they move from one position to another, they really don't mind temporarily being in between. Now in many of the other hard materials, for instance ceramic—like your typical coffee mug—that might be made up of two different kinds of atoms, and they are arranged in a very specific way. They don't want to switch positions at all. If you apply stress to it, the atoms will start to move, and there will be greater and greater resistance to that movement until, ultimately, it's actually easier for the material to fracture than to change shape. And so if you drop a metal mug, it will typically land, and it may dent, but if you drop a ceramic mug, it really doesn't have the ability to dent, and instead it cracks, and you end up with a broken mug.

NARRATOR: The art of sword fighting also requires its own kind of hardening by fire. Midori studies sword fighting technique three nights a week under the watchful eye of her father, Fumon Tanaka.

Tanaka is a grand master swordsman and believes that the samurais' code of honor and their values, called "Bushido," are important to maintain.

FUMON TANAKA (Samurai Grand Master): I think many Japanese people can still find the spirit of the Samurai in their hearts. We have started to judge everything with money, or if you own a big house, or drive a nice car. But the spirit of the warrior was different. Honor was more important; to give your best at all times was important. This is the spirit of Bushido that we should not forget.

NARRATOR: Midori started training when she was a small child, and her father hopes that she, too, will be a grand master.

MIDORI TANAKA: It is a lot of responsibility. I cannot let the tradition die out with my generation. So I practice everything I learn very hard.

NARRATOR: By any standard, Midori and her father have an unusual relationship, and an odd way of demonstrating their mutual respect. In this ancient test, Midori will shoot an arrow at her father's heart. He has only his sword to defend him.

The arrow can penetrate a board over one centimeter thick, more than enough to kill a man and to make a young student a little nervous.

Light, perfectly balanced and hard enough to cut through armor, in the hands of a fully trained samurai, the sword is the ultimate weapon for close combat. But can the sword save him from a speeding arrow?

It's not only Master Tanaka's ability to react in the face of a speeding arrow, but also the sharpness of his sword that allows him to sever it mid-flight and defend himself from his daughter's pointed barbs.

The samurai needs a sword that is both hard and flexible, but remember that there is a tradeoff. Hard metals, with more carbon, hold an edge but are brittle and can break. Tough metals bend, but can't hold an edge. Smelting creates pieces of both types which are then purified and shaped.

Now is the crucial moment when both types of steel are forged together. The hard steel is pounded flat and then folded into a u-shape. The tougher low-carbon steel is heated to a glowing red and inserted into the core. This relatively simple procedure is the culmination of a great deal of work and key to the ultimate success of the sword.

Now the metal the samurai needs is where it is most needed. The hard steel is wrapped around the outside to allow for the cutting edge to be razor sharp, and at the core, where the sword needs to absorb the impact of those deadly blows and be more flexible, Gassan uses the tougher steel.

RICHARD VINCI: The sword is an excellent example of people, first of all, understanding the requirements of the particular application, and then the ability to understand how to achieve those properties through the right choice of materials and through the right processing. So it's an excellent analogy for what people do when they build a complicated, modern, engineered structure.

NARRATOR: The success of the ancient swords' engineering was judged by a rating system that was as ghoulish as it was efficient. Sword testing and the criminal justice system of ancient Japan went hand in hand, so to speak. Depending on the severity of someone's crime, they could have an appendage chopped off. Stealing might lead to the loss of a hand; bigger crimes had more severe penalties.

RICHARD VINCI: By modern standards, testing a sword using actual body parts is, of course, really distasteful. But from a practical point of view, very effective, because that is really what the blade is designed to do.

MICHAEL NOTIS: A blade that would go through a body at its midsection was certified as a better blade than would go through, for example, somebody's wrist, or ankle. A blade that could go through two bodies, or three bodies, or four bodies, or even five bodies, as some inscriptions read, was believed to be the best blade. And those that are in existence today are in the best Japanese museums that you can find; a "five-body" blade.

NARRATOR: A "five-body" blade—think of it as a kind of grotesque Good Housekeeping Seal of Approval.

At Gassan's forge, a much more delicate work is underway. The final stage of the forging process will harden the steel to hold its razor sharp edge. It is done through a dramatic step of heating and quickly cooling the steel to lock in the carbon. This process, called quenching, will accentuate the hardness of the high-carbon steel but has little affect on the tough, more flexible, low-carbon steel.

RICHARD VINCI: Now I'm going to show you what happens when you heat and then quench a piece of low-carbon steel, similar to that that you'll find inside the core of the sword. In its initial form it bends, really, quite easily. Now I'm going to simulate the heating and quenching sequence that a smith would put the steel through, using a blowtorch. I'm going to heat the end of the steel rod here to the point where it's orange-hot, so the carbon has gone into solution. And, once the end is nice and hot, I'm going to plunge it into some cool water, very, very rapidly cooling it. And it retains most of its bendability.

Now, let's take look at the very-high-carbon steel. It's like the cutting edge of the sword. When it comes out of the box, just like the mild steel, I can bend it very easily. Let's see what affect this had with the high-carbon steel: very brittle, very easily broken. The material is very hard, but not very tough. If you had an entire sword made out of a material this hard, it would be very likely to shatter on the battlefield.

You could make a glass sword that would have a wonderfully sharp edge and might actually cut something one time, but very rapidly you'd see the shortcomings of following that kind of approach. You'd be emphasizing only hardness at the expense of other important properties, like toughness.

NARRATOR: Gassan prepares the sword for the dramatic quenching stage by painting on a secret mixture of clay and charcoal powder. This will insulate parts of the blade allowing some parts to cool even more quickly than other parts. In time, it will also reveal one of the most unique signatures of the samurai sword.

The sword is now ready for this crucial moment. Gassan darkens the forge so that he can judge, by the color of the metal, exactly when the sword edge has reached 1,500 degrees Fahrenheit. Too hot and the steel might crack, too cold and the quenching would fail.

MICHAEL NOTIS: The most critical time in the whole sequence is this quenching operation. As many as one out of three blades is lost at this point in time.

NARRATOR: Gassan is ready to pull the sword at a moment's notice.

RICHARD VINCI: When the smith plunges it into water, the two different parts of the sword are both contracting. The part with low carbon—this is the part inside the core of the blade—is able to contract pretty much like it would like to, because there's really not much carbon in there to be trapped. So it shrinks a lot. The part on the outer surface though, is filled with carbon, and so it's really prevented from shrinking as much as it would like to.

So, if you can imagine this part being the core of the blade and this part being the edge, the top part is going to shrink a lot more than the bottom part and when it does so, it automatically builds a curvature into the blade.

NARRATOR: The two types of steel contracting at different rates forces the blade to curve, giving the samurai sword its distinctive, body-hugging shape.

Risuke Otake is one of the world's finest martial arts experts. At 80 years old, he is still driven to pass on the way of the Samurai and teach how to use the unique curved sword to its best advantage.

RISUKE OTAKE: You should attack here and here, at the arteries and at the heart. If you cut from the other side you won't reach them. So attack here or attack the neck.

When you fight, you should never have the sun in your face, you should always keep the sun or the moon behind you. You can use it to blind your enemy. The best warrior is one who can turn circumstances to his advantage in a fight.

NARRATOR: To study with the master, every student takes a blood oath to uphold the true spirit of the samurai code. Only the most advanced students are allowed to trade in their fighting sticks for sharpened swords.

The final stage of this thousand-year-old craft will give the sword its legendary fighting edge. It will also make or break the value of the sword.

Master Takeshi Hon'ami is a 14th generation sword polisher. He will spend several weeks bringing the forged steel to a brilliant luster. It takes a lifetime to master this trade. Even learning how to sit isn't easy.

Hon'ami's polishing stones are rare and can cost a thousand dollars or more. After 10 days of polishing, he moves on to one of the finest stones, the jizuya, so small it is sometimes no bigger than a grain of rice.

Although he keeps the edge of the katana, or sword, turned away from his body, it takes extreme concentration to rub these stones against some of the sharpest steel in the world.

TAKESHI HON'AMI (Sword Polisher): Katanas are very sharp. When I was younger I used to cut myself a lot. Even these days, I'm still very nervous.

NARRATOR: It is only through his intensive polishing that the full beauty of the sword is achieved and a hidden beauty is revealed. Just before quenching, clay was painted onto the blade. Only now can the full effect of this be seen. Embedded in the steel is a visible line called the hamon. This wavy line is considered a great art form and is created by the skillful manipulation of the steel's inner structure.

RICHARD VINCI: What you will see in a macroscopic level is a difference in color or brightness on those two regions. What you're really seeing is a macroscopic effect that comes from the different arrangements at the atomic level in those two regions of the metal.

GASSAN SADATOSHI (Swordsmith): The creation of this line doesn't just show the skill of the swordsmith, it's also an expression of his creativity, and it gives every sword a unique character.

NARRATOR: The cutting edge is, of course, what the samurai sword is all about, and honing the sword's sharp tip is the last step in the process.

TAKESHI HON'AMI: We say making the tip is like applying makeup on your face, because the tip of the sword is what you show to the world.

NARRATOR: Beauty is in the eye of the beholder, whether that is expert swordsmanship, fast paced cinematic swordplay, or simply the quality of the sword metal itself.

For Midori and her father, the beauty of the sword is that it symbolizes important values from the past. Learning to use the sword is their way of keeping these traditions alive for future generations.

In modern Japan, there is a struggle between maintaining these traditions and embracing contemporary values. The lore of the samurai remains one of the key links to that past. Long after the gun had replaced swords as a weapon, Japanese soldiers in World War II still carried their swords into battle, although many were mass produced in the quickly industrializing war economy. Even today, when Japan's battles are economic not military, the reverence for the sword endures.

It has taken 15 people nearly six months to make this one sword. Blacksmith Gassan, finally, can now see the results.

GASSAN SADATOSHI: A sword that I spent so much time on, to see it finished, with all its characteristics brought fully to light, it leaves me speechless.

NARRATOR: Now finished, it is perhaps appropriate that even though the sword will never be used for its original purpose, thankfully, it has not lost any of its value in Japanese culture. Exceptional samurai swords can sell for hundreds of thousands of dollars as art objects and antiques.

So, today, the samurai sword has moved from the bloody battlefields to the rarefied—some would say cutthroat—world of art collectors, perhaps another sign of the legendary resilience that was engineered into the sword more than 1,000 years ago.