Japanese swordsmith quenches sword blade - GIF

[Jon]

Japanese swordsmith quenches sword blade. I guess this is how that iconic curve is made?



Previously:

Japanese game show: people compete to drill the tiniest hole - video
Japanese noodle cutter - GIF
Floor-by-floor Japanese building demolition - GIF and video
Japanese joinery animations
Japanese puzzle boxes
Quenching an anvil in a river, with an excavator - GIF
Quenching an enormous gear - GIF
Panzer tank hull being quenched
Giant gearshaft being quenched - GIF

[jimirwin]

Notice that the thinner edge cooled quicker & drew the curve the reverse of what we expect, then as the heavier back cools it draws the curve back to what we expect.
Amazing display! Imagine the stresses involved!

[Rorschach]

And thats why they crack so often!

[PJs]

Excellent display of differential heat treatment typical to Japanese swordsmith's to achieve a Sori curve seen here. A clay is used to protect and create the beautiful Hamons and holds the temperature of the thicker spine to cool slower. What happens metallurgicaly is kind of magical in just a few seconds as the edge shrinks the grain then relaxes as the spine begins to cool.

To think this was figured out so long ago with a lot of practice with rudimentary tools and knowledge (but good iron rich sand), a lot of testing and fractures and warps is what makes the people who made/make them so amazing and excellent tools and weapons.

[Philip Davies]

Notice the even colour throughout! I wonder whether that water is brine and whether it is at room temperature?