Silver 银，白银，also 金
Silver is a metal of little practical use. Like gold, it is too soft for tools and weapons. It is pretty when polished; but unlike gold, it tends to oxidise and gets covered in a black patina, which is not particularly attractive. In East Asia, silver long remained a very secondary metal that found limited applications for inlays, e.g. in bronze objects, and for some luxury or votive objects. It gained a new importance only in the late Tang in the 9th century, when it became a store of value used in overseas trade. Over the following centuries, the commercial economy and monetarization made silver the most desired metal. It functioned as an unminted money that was used by weight and fineness and assayed by private silversmiths and money shops until the end of the 19th century.
Most silver deposits in the investigated area are silver-lead ores, sometimes also mixed with zinc and copper ores. Extraction typically consisted of a separate preparation of rich silver ores and lead-silver ores, followed by the smelting of the latter for rich lead. The rich lead cakes were then cupelled, with the rich silver ores sprinkled in. Cupellation is employed to separate the noble metals gold and silver. It makes use of the fact that lead oxidises around 1000° C, below the melting point of the noble metals. Thus, the lead turns into liquid litharge with a relatively low density, which can be raked off the bath or absorbed into the porous material of the cupel, leaving the silver (or gold) (Yang and Kim 2019).
Silver (and gold) separation needed large amounts of metallic lead and produced small amounts of silver and large amounts of lead oxide. This technological necessity meant that the working of silver ores was easiest where lead ores were also available. If this was not the case, metallic lead had to be procured from elsewhere. During cupellation, some of the molten litharge (and a very small fraction of the noble metal) was vaporized. The litharge could be re-smelted to metallic lead (again losing a small percentage in the process) and thus re-cycled. Nevertheless, silver exploitation in the absence of lead deposits in the vicinity was costly and involved labour-intensive and polluting work steps. Most southwestern silver mines did not face this difficulty, as they exploited lead-silver deposits.
History up to the period of investigation
Silver appears in the archaeological and written record in the Han period (206 BCE-221 CE). In the earliest source, the Hanshu 汉书 (110 CE), silver and lead are already recorded in conjunction. For the Han period, the metal is recorded for central southern and southern Yunnan, for northeastern Yunnan (the famous Zhuti 朱提 silver) and also for the Baoshan 保山 region (Yang Shouchuan 2014 31). The only known specific site is Gejiu 个旧, identified by archaeological evidence and probably meant by the place name Yangshan in the west of Fengu 蕡古西羊山 (Hanshu 漢書).
Silver occurs as native silver, usually in small quantities as silver lock or fine root-like structures. Small finds of silver therefore can occur in the absence of mining. As the metal was of limited practical use, its exploitation by mining and smelting is relatively late and associated with cultural value. In the region, most ore deposits were composite ores of several metals, commonly of lead, frequently also of zinc, and not infrequently of copper, gold, cobalt, and sometimes titanium. Rich deposits are found in the cementation zone, especially where this zone coincides with the transition from limestone to layers of more compact rock of low porosity.
During the Nanzhao 南詔 and Dali periods 大理 (750-1253), the main use of silver was for votive objects. An expansion of silver mining is probable in the Dali kingdom (937–1253). An indication is that the royal family and nobility reportedly widely used silver tableware and other utensils.
The Mongol conquerors were known to extract bullions where they could, and the Mongol Yuan dynasty (1279-1368) placed considerable emphasis on gold and silver mining. The Yuan history, however, was compiled after the fall of the Yuan and by early Ming scholars in a fundamentalist agriculturalist climate. This work summarily reports the existence of silver mines, but only indicates the large regions of Weichu 威楚 (roughly the Chuxiong 楚雄 region), Dali 大理 (the larger Dali region), Jinchi 金齿 (the larger Baoshan region), Lin’an 临安 (the Yuxi-Honghe 玉溪——红河 region) and Yuanjian 元江 (southern Honghe). It may be added that the officially recorded revenues from silver mining were relatively modest. Exclusive of possibly considerable tribute tax directly presented to the court, the tax levied from silver mines recorded for the year 1328 was 735 ding 锭 and 34.3 liang 两 (Yang Shouchuan 2014, 51), converting to 1.361 tons.
We generally cannot identify the mines, but there is good reason to expect that numerous sites were exploited from the Han period, and that both the number and scale of the exploitations increased probably during the Nanzhao and certainly during the Dali and Yuan periods. At the same time, a considerable decline during the conquest years and during the period of climatic instability, population decline, and frequent rebellions in the later Yuan is probable.
Aubrey Hillman’s sediment core analyses of Lake Erhai has shown a boom in silver exploitation in this area that began in the early 12th and peaked in the late 13th century. Levels of lead pollution fell back to those of about 1110 only in the second half of the 15th century (Hillman et al 2015). The sediment record is evidence of extremely intensive extraction of silver and possibly also of gold. The interpretation is complicated by the uncertainty of the sites and questions about particle distribution with distance due to the mountainous terrain. Nevertheless, the extreme peak in the late Dali, the Yuan and the early Ming is without doubt.
The Ming-Qing period and results of the 2015-1018-project
Ming and Qing government records are relatively similar to those on copper, with occasional mention for the Ming and systematic tax registers from the Qing period. In addition, some mention of silver is found in private writings.
The official records are summary and clearly incomplete, with different types of records, such as the provincial gazetteers, the local gazetteers, and the veritable records, often incongruent. With occasional and private writings, however, written sources become more plentiful for the Ming, and especially for the Qing period.
We have some 40 names of mines in sources that date to the Ming period or are based on Ming records, and some 50 in Qing records. In the joint project by Yang Yuda and Nanny Kim 2015-2018, geolocation of these sites and visiting as many of them as possible was a core objective. We have now visited over 40 sites but still have not been able to identify about half a dozen.
Results of the project can be summarised in two maps, the first showing the outputs of the geolocated Qing sites as reconstructed from the fully official tax records as based on the revenue reported to the Ministry of Finance (hubu 户部), the second showing our reconstruction of outputs on the basis of slag dumps for a few sites where specific data were available, and comparative assessment based on remains and records for the other sites.
The completed project also led to a first reconstruction of smelting technologies and their transformations through the period from 1200-1850 (Yang & Kim 2019, Kim & Yang, forthcoming). This part of the research mainly analysed the written records, but added the study of remains of cupellation furnaces and their distribution to analyse the geographic dimensions and the historical depth of the application of the latest known technological development.
Research questions
For a more systematic approach, the current project uses lists of mineral deposits of the first half of the twentieth century. These were based on materials held in local archives, which again would most probably be records of local mining taxes and hence reflect historic exploitations, with some new or known but hitherto unexploited sites added. Extracting the entries that mention exploitation in the past or that list known silver mines only, a list of mines in Yunnan dated to 1915 includes 200 silver mines, while the provincial gazetteer of 1949 lists about 150. For areas of systematic case studies, we try to cover all historic mining sites. On this basis, we can analyse actual distributions and scopes of exploitation, as well as quantify the gap between mines in the official tax registers and those operated off the fully official records.
