Do you think he developed the technique after he found the huge chunk of black metal and realized he could make a crazy technique with it, or did he specifically search for a material that could take the stress of the technique that he envisioned?

Given how rare and valuable the 'xuan tie' that the HIS was made of, I wonder how long the process was for him to find or experiment enough to produce such a sword.

On a tangent, valuable weapons seem to be undervalued and glossed over; if someone like Ouyang Feng obtained the Heaven Sword, he might be able to instantly beat all the Greats considering they can't even block his weapon. It might be more valuable than the 9 Yin inside of it!