 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.