Japan has been making swords for over a thousand years. Samurai swords like katana are some of the most well-known weapons in the world. Even though it’s now possible to make replicas that look almost as good for a fraction of the price, making a true Japanese sword is a labor-intensive process that has stayed fundamentally the same for centuries.
But how exactly do you make a Japanese sword? Let’s find out.
Smelting
It starts with a clay furnace, called a tatara. For three days straight, the swordsmith and their assistants will layer iron sand and pine charcoal. The carbon in the charcoal mixes with the iron in the sand to produce steel.
They’ll carefully control the temperature so that high-carbon and low-carbon steel is kept separate. After using nearly 20 tons of sand and charcoal, the tatara is broken, revealing just 2 tons of steel, called kera.
The smith carefully breaks the kera this apart, separating it into soft hocho-tetsu and hard tamahagane. The former will form a flexible (by steel standards, anyway) core, while the latter is used to make the razor-sharp edge for which samurai swords are famous.
Each tatara can only be used once, and takes a week to construct. The time and expertise needed to produce kera means that it costs about 200 times more than regular steel. Even then, less than a third of it can actually be used in a sword.
Forging and Folding
Now that all the raw materials are ready, the smith can start forging. This might be the most well-known part of making Japanese swords. The smith folds and hammers the steel into layers up to 16 times — when finished, a single piece can have 30,000 layers.
This has a few benefits. Unlike Europe, Japan didn’t have great-quality iron to work with. It’s one of the reasons the process of making steel takes so long. Folding the steel like this spreads the carbon in it around, making each piece more regular in its characteristics. It also draws out impurities.
When we say “impurities,” we mean it. After all the forging has been done, sometimes only 1/10th of the original mass is left, and that’s after all the other metal that’s already been rejected earlier in the process.
Folding also lets you combine different kinds of steel. The balance of soft but flexible and sharp but brittle is crucial. The idea is to get a sword that can hold its sharpness, but also not shatter on impact. To do that in Japan with Japanese steel, you need to use different kinds of steel for different parts.
There are many different ways to achieve this. The hard steel can be folded into a U-shape and soft steel inserted along the spine for a kobuse blade. Honsanmai adds medium-strength steel to the sides to protect them while blocking or parrying. The legendary swordmaker Masamune combined seven different layers of different hardnesses in his soshu kitae technique.
As well as providing these practical benefits, folded steel looks really cool. Under the right light you can see lines and swirls that mark the different layers of steel. The patterns vary between schools and individual smiths, and are unique to each sword. Sometimes the smith will even add other metals, like copper, to create a more striking pattern.
The shape of sword at this point is pretty-much finished, but it differs from your mental image in one crucial way: it’s straight. Contrary to what you might have thought, katana aren’t hammered or bent into their shape. Instead, it gets its curve from heat-treating.
Heat Treatment
Once you’ve formed something out of metal, you’ll quench it by plunging it in water or oil to cool it quickly. This makes the metal much harder and stronger than if you just left it to cool naturally. In Europe, where the steel is pretty good and you make a sword out of a single piece of metal, you could dunk the whole thing in at once. Japan, however, makes their swords a bit differently. Or, should I say, differentially.
To augment the difference between soft and hard steel, the smith will cool different parts of the sword at different rates. This is known as (you guessed it) differential heat treatment. They’ll paint a clay mixture on the sword, covering the main blade but leaving the edge with little to nothing covering it.
Quenching is one of the riskiest parts of making a Japanese sword — as many as one in three swords can be ruined at this point. When the temperature just right, about 800ºC, the smith plunges the blade into a bucket of water.
The unprotected edge cools immediately and contracts. This quick cooling makes it even harder, and actually curves the sword forward. The clay-coated soft steel cools slower, making it softer and more flexible. As it cools, the contraction pulls the sword back and into the iconic katana curve that we all know and love.
This process creates another characteristic feature of Japanese swords: the hamon. That’s the line running along the sword. It shows the transition from hard edge to soft body made by the quenching. Like the layers of steel made during forging, the style of hamon varies greatly, from uniform and straight to complex peaks and waves.
Polishing
Finally, it’s time to polish and sharpen the sword. This is usually done by someone else, as it’s a discipline all of its own. Nowadays, a polisher will use seven different stones and take up to a month to finish a single blade. For museum pieces, this can cost $1,000 per inch of blade, so be careful where you leave those fingerprints!
The smith also won’t usually make the fittings of the sword, like the scabbard (saya) and handle (tsuba). Like polishing, that’s usually the job of a different person. While European swords are often considered inseparable from the fittings, with Japanese swords they’re not nearly as important. In a museum, you’ll often see just the blade displayed, and a single blade might be refitted several times as it changes owners.
Japanese Swords Today
Japanese swords continue to capture the imagination with their iconic features, unbelievably involved creation process, and the attention to detail and commitment that they represent. (Un)fortunately, the demand for swords as weapons to be used has fallen quite dramatically in the last few centuries. Accordingly, many swordsmiths have turned to knives as a way of applying the ancient craft to modern objects.
Gifu Prefecture, and especially the city of Seki, is well known for the quality of its blades, from katana all the way down to fruit knives. It takes about 10 years to become a knife maker here. If you want to make swords, you’ll need a government license, which is a process only slightly more labor-intensive than making a sword in the first place.
Asano Taro has done both. He began making knives when he was 13. At the age of 20, he began his sword-making apprenticeship as part of a school in Seki that stretches back to the 16th Century, then established his own kajiba forge in nearby Hashima.
Asano is one of the few masters who will allow tourists into his workshop. This is just as well, as 10 years is a long holiday by anyone’s standards. Under his watchful eye, you can make a samurai knife of your own – though do try to restrict yourself to chopping food rather than slaying your enemies with it.
It’s a rare opportunity to forge your knife under the instruction of a real master swordsmith. To book your slot in Asano-san’s atelier, click the button below. Book Your Knife Making Experience Now
Photo by @gogifu_japan
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