The Secret Method and the State: Official Attitudes Towards Wet Copper Production in Song China

Introduction

As base material for the production of cash coins, copper was the most important metal in the Chinese monetary system, and hence for the political economy of China, at least until the dawn of the silver age in the sixteenth century. During the Northern Song period, what Mark Elvin deemed a "medieval economic revolution" manifested itself in such phenomena as a more diverse division of labor, commercialization, and urbanization, along with the increased use of monetary transactions instead of barter.¹ This development was supported by a boom in copper production, which was tightly controlled by the state and employed as coinage to meet the aims of its monetary policy.² When ore deposits began to be exhausted and production costs increased, the diminishing output of copper developed into a risk for the currency system and the economy of the Song Empire. Relief was promised by early ideas of hydrometallurgy, methods that were known only to few as "secret methods" in the context of Daoist alchemy. With such processes as "gall copper" (dantong 膽銅), "steeping copper" (jintong 浸銅) or "leaching copper" (lintong 淋 銅), it became possible to use vitriol water (danshui 膽水, lit. "gall water"), an aqueous copper sulfate solution naturally occurring around weathered copper ore deposits, as well as vitriol earth (dantu 膽土, lit. "gall earth"), copper sulfate-bearing earth in similar locations, for the production of raw copper. These "wet copper methods" take advantage of a so-called "replacement reaction," through which copper precipitates on iron pieces placed in vitriol water and dissolves the iron, thereby turning the copper sulfate solution into an iron sulfate solution. The relatively pure copper obtained in this way could be refined with a relatively smaller expenditure of fuel than commonly mined copper ores worked with traditional methods of pyrometallurgy.³

For those controlling the affairs of the Northern Song state, who were responsible for procuring mint metals, this method of wet copper production became controversial from different perspectives. The large-scale application of secret methods from alchemistic contexts could be considered unethical or even dangerous, because the success of such methods was seen as being directly related to the morals and intentions of those who implemented them. Furthermore, the secrecy of these methods had a quasi-religious character in a Daoist context, so that publicly employing them could have entailed a heterodox religious challenge to Confucian learning. The seemingly inexplicable and spontaneous character of the process could also persuade statesmen that its end product could not be taken seriously as genuine copper and was just a fake.

However, these doubts were eventually overcome. During part of the Southern Song, when the overall production of copper had already fallen dramatically, wet copper methods even provided the lion's share of China's copper production. How this shift in discourse and practice took place cannot be reconstructed from extant historical sources. Still, three exemplary situations, in which individuals interested in promoting this technology encountered high representatives of the state, can cast three spotlights into the dark and provide insights into the development of official attitudes towards wet copper production in the Northern and Southern Song. In the first situation, between 1087 and 1089, a merchant suggested the application of the method to the Vice-Minister of Revenue and was harshly rejected. In the second instance, in 1094 a member of the Zhang 張 family, local elites from a copper-mining region in Jiangxi, gave a book about wet copper technology to the emperor, using careful words to justify its application, and was eventually entrusted with the establishment of the first wet copper facility in the empire. Third and finally, in 1210 the young official Hong Zikui sent a long prose poem about minting and metal production, in which he praised wet copper methods, to the court. His poem was well-received and he was employed thereafter as an instructor at the school for the imperial family (zongxue jiaoshou 宗學教授). From these three examples in the extant primary sources, the development of official attitudes towards wet copper production can be traced from being unacceptable, to becoming acceptable, and...