Why Zoro's susui blade is black?

Question

This is a quetion for anime lovers. Anyone who seen one piece and know this question's answer please help me get it.

Answer 1

Zoro sushi blades are not actually  created black they eventually become black. Infusing the blade with armament haki over and over again and fighting many battles with it that's why it eventually turned black.

Answer 2

This is also Zoro's 1st and only black sword. This sword is originally from the Wano-kuni and is considered as a national treasure. Zoro got this sword from Zombie Ryuma when he won their duel. This sword serves as a replacement to the destroyed Yubashiri.

Answer 3

Zoro's susui blade is black.

Zoro's susui blade is black because it is made of black steel.

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