The steel industry in China’s rustbelt province of Hebei, which surrounds Beijing, is sooner associated with choking smog than with beauty. But over 500 years ago, it produced a unique art form that still dazzles today.

Poor blacksmiths in the town of Nuanquan, in Hebei’s Yu county, found that if they hurled molten iron at the old city wall, it exploded in a shower of sparks in the cold night air. They donned sheepskins and straw hats to protect themselves, and used spoons made of hard willow wood to hurl the iron.

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