Coin history - The Song dynasty A.D. 960-1279 

15 of the 18 emperors during the Song dynasty issued coins. 45 reign titles in all were used on coins (counted in the Ding and Schjöth catalogues). The Song was in 1127 forced by the Ruzhen people of the Jin dynasty to move its capital from Kaifeng to Hangzhou in the South of China. The first part of the dynasty is called the Northern Song, and  the second period is called the Southern Song.
Song coins were issued with six kinds of calligraphy: the seal script (zhuanshu), the clerk script (lishu), the regular script (kaishu), the running script, the grass script (caoshu) and the thin gold script (see calligraphy). Each type of coin was produced in two or three styles. The regular script of the Shao Xing Yuan Bao has become the model for the most popular typeface used today which is called the Song type.
The first emperor had three reign titles, but the legend on his coins were Song Yuan Tong Bao which meant origin of Song. 
With regard to coinage, Northern Song was divided in three parts: Sichuan used for the most part iron coins, Shanxi and Shaanxi used both bronze and iron coins, and the rest of China used bronze coins. Iron coins were used in the south for mainly two reasons: one was because of shortage, the other was to prevent an outflow of bronze over the southern borders to the Qidan (Liao dynasty) and the Tanguts (Western Xia dynasty). In this belt bronze coins were prohibited, and all trade were done with iron coins (von Glahn p. 49).
Iron coins played an important role in the Song. In 1080 there were 26 mints, nine of them produced iron coins, approximately 900 million per year (Yang p. 28).
Iron coins were still used in the South alongside bronze coins during the Southern Song, but were no longer so important as during the Northern Song. From now on problems of copper shortage was resolved by issuing paper money.
Bronze coins were produced in enormous amounts in the Northern Song. In 961 the population were at least 32 million. In 1193 it was a maximum of 120 million (Chao p. 41). 
In 996 under the emperor Tai Zong 800.000 strings were cast (von Glahn p. 49). During Emperor Ying Zong’s reign three million strings were cast annually (Ren p. 57), but von Glahn writes (p. 247), that only some of the money that were cast were circulated. At the time when Kaifeng fell to the Jin conquerors, the state had accumulated 98 million strings, and that 30 million strings circulated among people. Even if the number of coins in strings was only around 800, the total number of coins at the end of Song would be around 90 billions! Even more coins than this must have been cast, since Song coins had become a universal currency in all of East Asia (von Glahn p. 248).  
The situation was much different in the Southern Song. Because of high mining and minting costs, the annual output was no more than 200.000 strings annually, often far less. Because of shortage of copper imperial edicts were frequently issued, which ordered all privately owned copper to be delivered to the mints. For the same reason, the coins of Southern Song contained at least 25% less copper in the alloy, than coins of Northern Song (von Glahn 50-51).

Because of the success of the Northern Song coins both in China and abroad, it was difficult even at peak production to produce enough coins, and paper money were issued to restore elasticity to the money supply  and secure the payment of taxes (von Glahn p. 248).

The second emperor Xiao Zong began to mark the year of issue on the reverse of his coins.
This practice was followed on most coins during the rest of the dynasty (D. Ren p. 75, 83).