How the Most Expensive Swords in the World Are Made

- This is a video about how Japanese

swords

are

made

,

swords

that are strong and sharp enough to cut a bullet in half. The access we got for this video is incredible. We were able to film everything from collecting iron sand to smelting the iron, forging the sword, sharpening and polishing it. They even let us use it. - That's so cool! - The method of making these swords has remained virtually unchanged for hundreds of years, all done by hand. They are still considered among the best in the

world

. - The Japanese

made

a weapon that was the best for their style of warfare and the materials they had on hand. - These swords are so prized that one from the 16th century has been valued at $105 million, making it the

most

expensive

sword ever built. (sword strikes) (dramatic music) (river noises) In the Shimane province of Japan there is a foundry that is on only one night a year where steel is made in the same way as 1,300 years ago.

It is known as the Tatara method, and only steel made this way ends up in the best Japanese swords. And they invited us to come film it. (drums and flute music) Shortly after 9:00 a.m. m., ceremonial prayers are said and a Shinto priest lights the fire. Everyone who will work at this foundry will be here for at least the next 24 hours. This includes Veritasium producer Petr. - I'm engaged. Let's do this. It's going to be fun. - Sword making in Japan dates back about 3,000 years, but at that time swords were made of bronze. We're not sure how people first learned to cast metal, but it was probably related to ceramics. - In the sense that you were using these rock oars to make glazes and things like that for ceramics in very controlled atmospheres.

And then we discovered that perhaps the potters found metallic beads in the bottom of the kilns in which they were firing it. Possibly this gave them the idea. - Bronze was discovered before steel because it is an alloy of copper and usually tin, both metals with melting points low enough to be melted in normal ceramic kilns. The problem with bronze is that, although it can be sharpened, it is too soft to hold an edge for long. So Japanese sword makers switched to steel 1,200 years ago, in the Heian period. This is what

most

people would recognize as a Japanese sword.

It is made of steel with a curved blade. Steel is an alloy of iron, the fourth most common element in the Earth's crust. The

world

's oceans used to be rich in dissolved iron. But two and a half billion years ago, cyanobacteria began photosynthesizing and creating oxygen. The iron reacted with that oxygen, precipitating from solution to settle on the ocean floor. By the way, the cyanobacteria were poisoned by the oxygen they themselves produced, so it is believed that when the levels increased enough, they died and, as a result, the oxygen levels decreased and iron no longer precipitated from solution.

Then the cyanobacteria could multiply again and the cycle would repeat itself. That's why most of the world's iron is found in layers of sedimentary rock called banded iron formations. Each layer of iron formed during a global bloom of cyanobacteria that infused the ocean with oxygen. Most of the world's iron supply comes from these banded iron formations due to their high iron concentration, up to about 60% by weight iron oxide. (soft music) But Japan, with its mainly volcanic geology, hardly has these sedimentary iron oxides. And this is probably the reason why the country was late to the steel production game.

Archaeologists have found steel artifacts in Anatolia, present-day Turkey, that are almost 4,000 years old. But in Japan, metals, including steel, were imported from China and Korea until the 8th century, when Japan began making its own steel. So where did they get the raw materials? Well, igneous rocks like granite and diorite still contain iron oxides, just in much lower concentrations. But as the mountains wear down, these iron oxides break down and are carried downstream. Over time they become part of the sand. The Japanese noticed that because iron oxides are denser than other minerals in sand, they accumulate in places where the river changes direction or speed.

Heavier iron sinks to the bottom and lighter material drags away. To amplify this effect, they deliberately created diversions in the river to increase the concentration of iron. - What you do is build a dam on a section of the river and then drag sand into it. Because the iron is heavier than the other parts of the sand, it is what is left behind and everything else is carried downstream. - With this method, iron sands with 80% by weight of iron oxides can be obtained. It is more concentrated than high-quality iron ore. And because it has fewer impurities, it is an excellent source of high-quality steel.

If you heat those iron oxides to over 1250 degrees Celsius, you can break the bonds with oxygen and get pure iron. But pure iron is actually softer than bronze. Thus, in its elemental state, iron offers no advantage. But nature gave humans a lucky break. One of the few ways to heat something up to 1250 degrees 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. - Yes, many people see it as a heat process. I see it as a chemical process. - Alloys are usually stronger than pure metals because they contain atoms of different sizes, and this reduces the ability of the atoms to slide past each other when an external force is applied. - So they just gave me some gloves, other gloves and a towel.

So things are getting very real. I'm really quite worried. (serious music) Here is the room with all the coal we are going to use during the night. There are just bags and bags of this stuff. (charcoal rattles) (flame crackles) There is a Buddhist saying: "Before enlightenment, chop wood, carry water. After enlightenment, chop firewood, carry water." So I guess we're lining up on all four corners. (charcoal rattles) Oh. Oh boy. I didn't do a great job with it. (laughter) (thunder) Then the rain comes, so we're quickly taking out all the coal and then measuring it. So each bag of these is 10 kilos.

Well. (serious music) So with iron sand, it mixes with water because if you don't mix it with water and put it in the flame, it just flies up. But if you mix it with too much water, then there will be water that will become hot. It will turn into water vapor and the entire oven could explode. What's scary is that they do it by touch. They are mixed with enough water until the iron sand is clumpy. But again, if it's too much, the whole thing could explode. Okay, put some iron. It is just after four in the afternoon and in the last few hours we have added 250 kilograms of coal and almost 60 kilograms of iron sand.

So yes, it's a slow process, but I think we're starting to get somewhere. I have no idea because the thing is obviously hidden, but it should be growing. - To achieve the high temperatures necessary to make steel, a strong and constant supply of oxygen is needed. For hundreds of years this was provided by huge foot-operated bellows. Many men would have needed a full-body effort 24 hours a day to maintain the temperature of the oven. - When I came here, I was a little sad that the bellows were electric. I really wanted to have this proper experience, to have this proper exercise of stepping on these bellows for 24 hours. (serious music) - The temperature inside the foundry reaches 1500 degrees Celsius, just below the melting point of iron, which is 1538 Celsius.

So the iron that is molten is not liquid, but it is soft and malleable enough to clump together into a large block of iron. No matter the quality of iron sand, there will always be some impurities, such as sulfur, phosphorus and silicon oxides. They combine with the carbon in coal and melt at a lower temperature than iron, so they become liquid and flow to the bottom. This is known as slag. After many more hours adding charcoal and iron sand, it is time for the first removal of the slag. Before the first slag removal, another prayer is said. (Steelworkers applaud) - Oh, that's crazy. (slag sizzling) (serious music) (hammer bang) Wow.

For the last three hours, we have been performing three processes. One adds the coal, two adds the iron sand and three opens the smelter from the bottom to break up the impurities so they can flow. (shovels scraping) I just want you to know that it's 3:16 in the morning and I'm still here and I'm very sleepy. (soft music) So it's currently six in the morning the next day. We have been melting for 21 hours. I'm exhausted but the sun is about to rise and it's been pretty amazing, I have to be honest. We have to close these doors real quick before they get mad at me. - At 9:00 the next morning the casting is completed.

A total of 614 kilograms of iron sand and 670 kilograms of charcoal were added to the foundry. At this point, in a traditional foundry, the only way to get the steel out would be to break it. Today a crane is used to dismantle the foundry. - Oh, wow, okay. Oh! - And what remains of all that hard work is a 100-kilogram block of steel, iron and slag. Only about a third of this block is of sufficient quality to be used in sword making. (the crane hums and makes metallic noises) - Oh, that's crazy. That's so cool. The result of all the hard work.

This is the first step in making a Japanese sword. (soft music) - Steel is sorted by quality and carbon content, which is also done by eye; In fact, this is one of the exams you must pass to become certified as a blacksmith. The different grades of steel are then sent to one of 300 blacksmiths across the country. Only 30 do it as a full-time job, and one of them is Akihara Kokaji, who we went to visit next. This is when the forging of the sword begins. In a coal-fired furnace with manually pumped bellows, steel is heated until it is soft and malleable.

Then, using hammers, the master swordsman flattens the steel. In the old days this would have been done by the blacksmith and three apprentices. The blacksmith, using a smaller hammer, set the pace and the apprentices used large mallets to flatten the steel. (hammers bang) (Petr grunts) - Woo. That was terrifying. - Today electric hammers are used. When the steel is flat enough, it is folded back on itself (the fire crackles) and then struck again to press the steel back into a solid block. (soft music) So why go to all this effort to flatten the steel, only to bend it back on itself and end up with a piece of steel the same size as before?

Well, because folding does two very important things. First, it spreads impurities such as silicon, sulfur and phosphorus. It spreads them all over the steel. This ensures a uniform consistency with no weak spots. Secondly, it gives grain to the steel. After bending the sword, it is now reinforced in the direction it will be struck in combat, and as an added benefit, the steel is exposed to the air. Therefore, there is a small amount of oxidation that creates a darker colored steel that, when folded, forms beautiful patterns. There are some swords that have more than a billion layers.

Now this doesn't mean that the sword has been folded a billion times, as each fold doubles the number of layers, so you only need about 30 folds to get a billion layers. But typically a sword is folded 10 to 13 times, resulting in a few thousand layers of steel. Now, a blade is not made from a single block of steel. The carbon content affects the hardness of the steel. That is why different percentages of carbon are used in different parts of the blade. Because carbon atoms are much smaller than iron atoms, they can fit inside the iron crystal lattice.

These trapped carbon atoms then apply an outward force to the lattice, putting the steel under tension. The higher the percentage of carbon, the harder and stiffer the steel will be. But this toughness comes at a cost. Steel becomes brittle, making it more likely to chip and break rather than bend. So what blacksmiths do is 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 and be able to maintain a sharp edge for a long time. But the spine is usually made of low-carbon steel, which allows the sword to flex without breaking.

This is done by welding pieces of steel with different carbon contents. - So we have a break of about 15 minutes because you know the iron takes a little while to heat up and thenmerge, and then we're back there. It's really hot. It's very, very hot in there. It's amazing that I can do this for four hours straight. - After hammering the sword into shape, which is a straight blade, it is covered with a layer of clay, a thick layer for the spine and a thin layer for the blade itself. It is then heated in the oven and then quickly cooled in water, a process known as quenching.

Now, because the layers of clay have different thicknesses, the cooling rate is faster for the edge than for the spine. When the steel is heated, the carbon enters the iron lattice and, since the spine of the sword is covered in thick clay, it will cool slowly, giving the carbon atoms time to leave the iron matrix. This will result in a very low carbon steel called ferrite, but the carbon atoms that left the matrix will be trapped by other iron atoms and create a type of steel known as cementite. The combination of ferrite and cementite is known as pearlite, and is a mostly soft and ductile form of steel, although some parts are hard due to the cementite.

Then per light forms the spine of the sword. In contrast, the very thin layer of clay on the blade means that it cools very quickly, so more carbon is trapped in the web. This forces the lattice structure to change from cubic to tetragonal, generating a form of steel known as martensite. Since the trapped carbon puts pressure on the lattice, martensite is incredibly hard, exactly what you'd want for the edge of a sword. The tetragonal lattice structure of martensite 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 martensite formation. In fact, you can 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 border pattern. - In the Victoria Albert Museum in London there is a Japanese sword that has a very detailed small dragon on the hamon, and I have looked at it many times. I don't know, okay, I don't know how he did that. (laughs) - About a third of all leaves break during the cooling process. - You turn it off once and thank the stars you did. -The sword is then placed back into the forage to evaporate the remaining water.

This also provides some energy to loosen some of the crystalline structures and make the sword less brittle. - And that's about the extent of the tempering process on a Japanese sword, which might be enough to loosen things up a bit, but they kept the edge much harder than in the West. - Once the sword is forged, it is sent to a polisher. Polishing and sharpening a sword is also done by hand with sharpening stones of different thicknesses. It can take a month to sharpen and polish a single sword. - One of the things I love is that this table is tilted and the entire floor there is tilted down.

So whenever you want, add the water, all the waste and all the water, you know, flows downhill, so it's not perfectly flat. (hammer taps gently) - Sometimes swords are also engraved with beautiful designs, although this is quite rare. And after all that, the sword is ready. To learn how to use a Japanese sword, Petr received a lesson from a master, Takara Takanashi. He is the tenth generation student of Miyamoto 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 over 60 duels to the death and won every last one of them. (serious music) (soft music) There is a story about a duel that took place during a snowstorm. As he faced his opponent, katana extended, Musashi was so calm and held his sword so still that snowflakes began to gather on the thin edge of the blade. -So during the lesson I thought I could use a katana, but instead we spent the whole time learning how to take the blade out of his sheath and then put it back in. So when I actually had the opportunity to use a katana to cut some things, I was completely unprepared. (katana strikes) (playful music) - Well, it looks like it's your turn.

I'm so scared. Well, this has been an incredible day. We've seen some beautiful katanas and now these wonderful people are allowing me to use one of their incredibly beautiful works of art to cut some things. (Petr exhales heavily) (katana hits) - Oh. Oh. - Wow! As if this is the best day ever. (soft music) - There really is something extraordinary about Japanese swords. The amount of care, attention and experience each step requires, from collecting and refining iron sand to smelting, forging and sharpening a sword, each step requires a lot of time and skill. It's amazing that all of these things were discovered through trial and error to produce such high-quality artifacts that are still prized centuries later. (steelworkers speaking Japanese) (steelworkers applauding) - Before making this video, I didn't really appreciate that swords could be art.

For me, it's a good reminder that whatever you do, you should do it with great care, attention to detail, and love for the craft. (both speak Japanese) - Do it enough times and you might just get something beautiful. (audio bells and trills) Hey, Henson Shaving brought you this part of the video. You know, making high quality stuff is hard, and as far as I'm concerned, Henson makes the highest quality razors in the world, the katanas of the shaving world, if you will. I have been using his AL-13 shaver for the last year and it is by far the best shaver I have ever used.

One of the reasons for this is that Henson really understands the physics of shaving, because as aerospace machinists for 20 years, they know how to cut things effectively. They get precision. Human hair is much harder than the skin from which it grows, and as a result, typical razors drag and pull on the hair as they cut it. What a multi-blade shaver does is assume that the first cut will be ineffective, so it incorporates additional blades to cut the hair before it returns to position. And that results in a good cut, but it also increases friction, which causes burns and skin irritation.

Henson carefully studied that problem and realized that it was not necessary to add additional sheets, he only needed to properly support a single sheet. Virtually all knives allow too much play in the blade, but not Henson. The result is an effective cut without additional friction on the skin. Seriously, a Henson really is a great razor. It will last you a lifetime. You'll get a better shave with less irritation and you'll also save money in the long run. So head to hensonshaving.com/veritasium or scan the QR code here and enter the code “veritasium” to get a hundred free blades with the purchase of any razor.

I want to thank Henson Shaving for supporting Veritasium and I want to thank you for watching.