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How Japanese Masters Turn Sand Into Swords

Veritasium・18 minutes read

Japanese swords are crafted using traditional methods, valued for their quality and history, with one 16th-century sword being the most expensive ever at $105 million. The intricate process involves steel-making using the Tatara method, careful selection of materials, forging, and meticulous finishing to create a blade with a distinctive curve and visible steel boundaries known as hamon.

Insights

  • Japanese swords are crafted using a centuries-old method that involves sourcing iron sand from rivers in Japan, smelting steel once a year in a traditional Tatara method smelter, and meticulously hand-forging the blades by skilled swordsmiths like Akihara Kokaji.
  • The intricate process of making Japanese swords includes folding the steel to evenly distribute impurities, using varying carbon percentages in different parts of the blade to balance hardness and flexibility, and quenching the sword in water to create a hard edge, resulting in a blade with a visible hamon pattern and iconic curve.

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Recent questions

  • How are Japanese swords made?

    Japanese swords are crafted using a traditional method that involves handcrafting each step. The steel is made using the Tatara method, where iron sand is heated with charcoal to create pure iron, which is then alloyed with carbon to form steel. The steel is then sorted by quality and carbon content, with different grades sent to swordsmiths who forge the swords by heating, flattening, and folding the steel. The folding process spreads impurities evenly, creating a grain that reinforces the blade and produces beautiful patterns. Different carbon percentages are used in various parts of the blade to balance hardness and flexibility, with high carbon content for the edge and lower-carbon steel for the spine. The sword is then quenched, tempered, polished, and sharpened by hand with whetstones.

  • What is the most expensive Japanese sword?

    The most expensive Japanese sword is valued at $105 million, making it the priciest ever. This sword, dating back to the 16th century, is considered among the best globally.

  • Where is the iron sand for Japanese swords sourced?

    The iron sand used for making Japanese swords is sourced from rivers in Japan. Iron oxides accumulate in these rivers due to deliberate diversions, providing the necessary material for steel-making.

  • How is the iconic curve of a samurai sword formed?

    The iconic curve of a samurai sword is formed during the quenching process. The sword is covered in clay with varying thicknesses, heated, and rapidly cooled in water. This rapid cooling results in the formation of martensite, which gives the sword its distinctive curve.

  • What is the significance of folding steel in Japanese sword-making?

    Folding steel in Japanese sword-making is a crucial step that spreads impurities evenly and creates a grain in the steel. This process reinforces the blade, making it stronger, and also produces beautiful patterns from oxidation. Different carbon percentages are used in various parts of the blade to balance hardness and flexibility, with the folding process playing a key role in achieving these desired characteristics.

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Summary

00:00

"Traditional Japanese Sword Making Process Revealed"

  • Japanese swords are made using a traditional method that has remained unchanged for hundreds of years, with all steps done by hand.
  • The swords are considered among the best globally, with one from the 16th century valued at $105 million, making it the most expensive ever.
  • Steel for the swords is made using the Tatara method in Japan, where steel is produced once a year in a smelter lit for only one night.
  • The iron sand used for steel-making in Japan is sourced from rivers, where iron oxides accumulate due to deliberate diversions.
  • Iron sand with 80% iron oxides by weight is heated with charcoal to over 1,250 degrees Celsius to create pure iron, which is then alloyed with carbon to form steel.
  • The steel-making process involves adding charcoal and iron sand over hours, with impurities like sulfur and phosphorus forming slag that is removed periodically.
  • After 24 hours of smelting, a 100-kilogram block of steel, iron, and slag is produced, with only a third being of high enough quality for sword making.
  • The steel is sorted by quality and carbon content, with different grades sent to swordsmiths, like Akihara Kokaji, who forge the swords by heating, flattening, and folding the steel.
  • Folding the steel spreads impurities evenly and creates a grain, reinforcing the blade and producing beautiful patterns from oxidation.
  • Different carbon percentages are used in various parts of the blade to balance hardness and flexibility, with higher carbon content making the steel harder but more brittle.

16:46

"Crafting Samurai Swords: Steel, Heat, Precision"

  • Swordsmiths use steel with different carbon contents for various parts of the blade, with high carbon steel for the edge and lower-carbon steel for the spine.
  • The process involves welding together steel pieces with different carbon contents, followed by heating and melding the iron for about 15 minutes.
  • After hammering the sword into shape, it is covered in clay with varying thicknesses, heated, and rapidly cooled in water, a process known as quenching.
  • The spine of the sword forms from a combination of ferrite and cementite, while the edge forms martensite due to the rapid cooling, resulting in a hard edge.
  • The iconic curve of a samurai sword comes from the formation of martensite, and the boundary between different steel types is visible in the finished sword as hamon.
  • The sword is then tempered, polished, and sharpened by hand with whetstones of different coarsenesses, a process that can take up to a month.
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