1 Cash - Qianlong Tongbao, Boo-chiowan, palace coin

The Board of Revenue Mint in Beijing operated two furnace halls — Boo-chiowan (源局) and Boo-yuwan (裕局) — producing cash coins under tightly regulated quotas throughout the Qianlong reign. "Palace coins" from this mint were held to a noticeably higher standard of alloy and finish than provincial issues, reflecting the court's insistence that Beijing-struck cash maintain a fixed brass ratio at a time when distant provincial mints were routinely debasing their output with higher zinc or lead content. The Yunnan copper supply disruptions of the mid-18th century made that discipline increasingly difficult to maintain.