Qianlong Tongbao (; Vietnamese: Càn Long Thông Bảo) is an inscription used on cash coins produced under the reign of the Qianlong Emperor of the Qing dynasty. Initially the Qianlong Tongbao cash coins were equal to its predecessors in their weight and quality but as expensive military expenditures such as the Ten Great Campaigns began to take their financial toll on the government of the Qing dynasty the quality of these cash coins started to steadily decrease. The weight of the Qianlong Tongbao was changed several times and tin was added to their alloy to both reduce costs and to prevent people from melting down the coins to make utensils. As the intrinsic value of these coins was higher than their nominal value many provincial mints started reporting annual losses and were forced to close down, meanwhile the copper content of the coinage continued to be lowered while the copper mines of China were depleting. The Qianlong era also saw the conquest of Xinjiang and the introduction of cash coins to this new region of the Qing Empire.
As a reminder to the people of Xinjiang that the Manchus conquered the region one in five cash coins produced in that region after the death of the Qianlong Emperor was ordered to bear the inscription "Qianlong Tongbao" (Emperor Qianlong Money), as a consequence cash coins with this inscription continued to be produced until the end of the dynasty.
History
During the first few years of the reign of the Qianlong Emperor China had suffered from a shortage of cash coins due to the contemporary scarcity of copper, but soon Yunnan's copper mines started producing a large surplus of copper allowing the Qing government to swiftly increase the money supply and minting more coins at a faster pace. The cash coins produced during this early period are similar in size and quality as the preceding Kangxi Tongbao (康熙通寶) and Yongzheng Tongbao (雍正通寶) cash coins, but over time the quality and size of the Qianlong Tongbao would deteriorate. Like the preceding Yongzheng Tongbao coinage all Qianlong Tongbao cash coins exclusively use Manchu mint marks characterised by the character "" (Boo) on the left side and the name of the issuing mint in the Manchu language on the right. A special characteristic of some Qianlong Tongbao cash coins is that the Chinese character "Long" (隆) at the bottom is sometimes written with a "Fou" (缶) instead of the usual "Sheng" (生).
The Qianlong era saw the founding of the Zhili mint in the city of Baoding (保定) as well as several mints in the newly conquered region of Xinjiang, some of these mints oversaw the production of "red cash coins" (紅錢) which were made of nearly pure copper. In the middle of the Qianlong era as much as 3,700,000 strings of cash were produced annually. Early Qianlong Tongbao cash coins contained no tin and were referred to as "yellow cash coins" (黃錢), however in 1740 2% tin was added and in 1741 coins were ordered to be made of an alloy of 50% copper, 41.5% zinc, 6.5% lead, and 2% tin to reduce the likelihood of people melting down coins to make utensils, did not allow to reuse the material because it would become brittle and objects would more easily break. All while the Qing government encouraged to sell their utensils to the state mints to be melted into coinage, these cash coins are commonly referred to as "green cash coins" (青錢) even though their colour appears to be just as yellow as the earlier cash coins. The production cost of these new Qianlong Tongbao cash coins was about 15% of the material value and their intrinsic value exceeded their nominal one. Yet in actuality not all provincial mints followed the imperial directive to change the alloy of the coinage and continued to produce the cheaper copper-zinc alloy which was used before. From this period onwards the Ministry of Public Works Mint manufactured 12,490 strings of cash coins annually (with 1,000 cash coins per string).
By the end of the Qianlong era Yunnan's copper mines started depleting the production of cash coins was lowered by the end of the Qianlong era, and the copper content was debased once more. 1794 all provincial mints were forced to close their doors, but subsequently reopened in 1796.