# How is this done?



## Seffers93 (Jan 7, 2021)

Hey guys, 

I always wonder how this look is achieved. I’ve tried looking it up but I’m probably not using the proper vocabulary to find the answers I’m after.

I’m wondering how they keep the high portion of the blade (toward the spine) dark. Is it just left from grinding after forging and heat treat? Or is it like a San mai that has a more etch-reactive steel on the outer layer?

Just curious. Thanks in advance!


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## TB_London (Jan 7, 2021)

It’s normally referred to as kurouchi or forged finish. 
When you heat the metal to forging temperatures the metal oxidises to form forge scale. If you don’t grind this off in subsequent steps it remains and can protect the knife to a degree from rusting.

Relies on the maker forging the blade to shape and then grinding less, and most blacksmiths would rather forge than grind so is better to maker.


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## Nemo (Jan 7, 2021)

Yup, Kurochi in Japanese; Blacksmith's Finish in English.

When the steel is heated to austenising temperatures (circa 750 celcius), the surface steel oxidises and looks like this. Chemically, I guess it's a bit like a super patina. All knives are 'born' like this (unless heat treated in an anoxic environment) but most have it ground off during finishing.


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## Nemo (Jan 7, 2021)

I should add, that this finish can be mimicked by the use of blueing compunds (which are basically strong acids that force a strong patina). Real kurochi tends to be textured (unless partially ground down) While blued fake kurochi is smooth.


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## Seffers93 (Jan 7, 2021)

TB_London said:


> It’s normally referred to as kurouchi or forged finish.
> When you heat the metal to forging temperatures the metal oxidises to form forge scale. If you don’t grind this off in subsequent steps it remains and can protect the knife to a degree from rusting.
> 
> Relies on the maker forging the blade to shape and then grinding less, and most blacksmiths would rather forge than grind so is better to maker.





Nemo said:


> Yup, Kurochi in Japanese; Blacksmith's Finish in English.
> 
> When the steel is heated to austenising temperatures (circa 750 celcius), the surface steel oxidises and looks like this. Chemically, I guess it's a bit like a super patina. All knives are 'born' like this (unless heat treated in an anoxic environment) but most have it ground off during finishing.



Thanks for the info! Good to know!


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## Jesse Killion (Jan 8, 2021)

Theres a way to get some of the pitting as well, if that is what you are looking for. If you use cold bluing on the blade and then put the knife into bleach, while the cold bluing is still wet, it will give some of that pitting effect. I would recommend doing this process outside as I'm pretty sure the gases put off by this are not all that good for you.


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