Japanese swordsmith quenches sword blade - GIF

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

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Previously:

https://www.homemadetools.net/forum/...709#post118686
https://www.homemadetools.net/forum/...383#post104152
https://www.homemadetools.net/forum/...2738#post97014
https://www.homemadetools.net/forum/...2258#post76045
https://www.homemadetools.net/forum/...1659#post74870
https://www.homemadetools.net/forum/...213#post121319
https://www.homemadetools.net/forum/...3582#post99502
https://www.homemadetools.net/forum/...2504#post96473
https://www.homemadetools.net/forum/...158#post100892

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!

And thats why they crack so often!

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.

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