In September 1734, the air along East Straight Street in Huize County filled with the sulfurous scent of burning charcoal and the intense heat of molten metal. Here, at the newly established Baoyun Old Mint Bureau—known locally as the Old Copper Shop—the Qing Empire began minting its own currency directly at the source of its copper supply. This massive operation reducing the need to transport large quantities of raw Yunnan copper to distant imperial mints..

Inside the north-facing, 11,000-square-meter compound, a systematic industrial city operated along a grand central axis. Visitors passed through the main gate, a ceremonial gate, and a grand hall, eventually reaching a temple dedicated to the God of the Furnace. Flanking this axis, a network of over 200 timber-framed rooms hummed with activity. In the charcoal houses, workers shoveled fuel. In the engraving rooms, specialists carved the Manchu characters for "Baoyun" into coin molds. Blacksmiths and carpenters repaired tools, while guards patrolled the copper, lead, and tin warehouses.

At the heart of the facility, 588 head-casters and laborers tended 28 roaring casting furnaces. They poured glowing, liquid alloy into molds, producing 125,682 strings of "Yongzheng Tongbao" coins annually. The heavy clink of cooling metal marked the heartbeat of Southwest China's financial center.

This intense production lasted until 1736, when the Old Mint Bureau ceased active casting. To meet growing monetary demands, the government established the Baoyun New Mint Bureau nearby in 1741, creating a unique administrative system of "One Prefecture, Two Mint Bureaus."

Today, the grand axis is gone, largely lost to urban development. Only three dilapidated, tile-roofed wooden structures survive, standing quietly on the grounds of the Fanghua Building Materials Company, where a steel frame factory later operated. Registered as a protected cultural relic in 1999, these remaining timbers offer a direct physical connection to the historic "Southern Copper Transported North" network, reminding us of the human labor that once forged the empire's wealth.