1 Cash - Xianfeng Tongbao, Boo-yuwan, zinc

Zinc cash coins from the Boo-yuwan (Board of Works) mint represent one of the more desperate monetary experiments of the Taiping Rebellion period. With copper supplies severely disrupted and the Qing treasury under acute strain from military expenditure, the Board of Works briefly authorized zinc as a substitute coinage metal in the mid-1850s. The alloy was unpopular — zinc coins corrode aggressively in humid conditions and were widely rejected by merchants and the public alike.

Surviving examples in any condition above poor are genuinely scarce. The combination of low original acceptance, active corrosion, and the general chaos of the period accounts for it.