The insertion of bones into the kiln is a key to his success.
One Chinese technique for sword-making involved adding a bit of person into the mix. National Geographic tracked down this practice in present-day Taiwan.
One sword-maker explains:
"In the past there's been a saying that if one wants to make a good sword, one needs human bones. By chance, my friend was collecting bones (from the deceased). Then I just asked him to give me some human bones for forging swords."