Counterfeiting activities during the Tang Dynasty (618–907 CE) revealed by the special alloy coins in the Chenzhou hoard, Hunan, China

Kaiyuan Tongbao coin was the primary circulation currency during the Tang Dynasty. It defined the Chinese coinage model for over a thousand years afterward. Despite repeated government prohibition, coin counter-feiting prevailed through Tang Dynasty. Such activities resulted in a large amount of counterfeit coins entering the market, which undermined economy and led to social instability. However, as a key to exploring the issue of counterfeiting, information on the alloy composition, provenance and the production mode of the counterfeit coins are not yet clear. This paper presents the first comprehensive scientific study on counterfeit coins from a hoard in Hunan Province in South China (a total of 39 kg and approximately 8000 coins were found). Radio-carbon dating of the bamboo weaving wrapped coins indicated that the hoard dated from 668 to 874 CE (Tang Dynasty). Chemical composition analysis, morphological and metallographic images and lead isotope analysis of 78 hoarded Kaiyuan Tongbao coins had been obtained. Combined with historical records, ore materials probably originated from the local Huangshaping and Baoshan polymetallic deposits in the Nanling metallogenic belt in South China. Results showed that there were 16 types of alloy materials, primarily cast alloys of the Cu-Fe-As system. Most of the coins were minted using a Cu-Pb syngenetic ore rich in many elements from Fe, As, Sb, and Sn. One discovery is the utilizing of a by-product of local ore smelting which was called the speiss. The hoard coins studied in this paper provide the first evidence of the use of speiss for coinage in ancient China. Such material sources and manufacture technique made convenience for coin counterfeiting, which explains repeated failures of central government's attempts to eliminate coin counterfeiting, especially for those mining areas.