Crucible smelting in Shanxi

A typical landscape in Shanxi, ca. 1930. (George Babcock Cressey, China’s geographic foundations: A survey of the land and its people, New York 1934, p. 185).

Shanxi seems fitted out by nature for the iron industry, with the world’s largest deposit of coal, reasonably large reserves of iron ore, refractory clay, limestone, and not much else in the way of raw materials for industry. And conditions are not good for agriculture, with poor soil and a dry climate. Consequently, the iron industry has been, at least in the past few centuries, the dominant economic activity. Coal mining and iron production were sideline occupations for a large part of the peasant population, but it seems that there were also large areas in which iron making was the only occupation. In Yincheng 荫城, a town with a population of perhaps 5,000, when a foreign visitor in 1898 asked how people lived without agriculture he was told, ‘We eat iron’ (Shockley 1904: 850).

Crucible smelting of iron in Gaoping county, Shanxi, 1898. (Transactions of the American Institute of Mining Engineers, 1904, 34, fig. 1, opposite p. 854).

The earliest description of the distinctive ‘crucible smelting’ technology used in Shanxi is that of Ferdinand von Richthofen in 1870. A mixture of ore and charcoal is packed in sealed crucibles which are heated, using more coal as the fuel, to around 1200°C for a few days. The iron oxides in the ore are reduced to metallic iron by the coal in the crucible. With this technique there were no great economies of scale and, as Richthofen notes, all of the ironworks were very small. Liu Peifeng et al. (2017) have collected all of the written descriptions of crucible smelting and produced a very useful report with considerable technical detail.

The earliest mention of crucible smelting is in Boshan xianzhi 博山县志 (Gazetteer of Boshan County), published in 1753. Boshan is in Shandong, and the text states that the technique of crucible smelting was introduced here from Shanxi in 1663 by Sun Yanquan 孙延铨. This man included a poem on iron smelting in his book Yanshan zaji 颜山杂记, completed in 1664.The poem is difficult to interpret, but it seems to describe crucible smelting (Liu Peifeng et al. 2014).

Shanxi produced in 1870 about 130,000 tons of iron per year. This is an enormous amount, more than we know of from all the rest of China at the time. (It must be remembered that, throughout China, there undoubtedly was much production for local consumption about which we know nothing.) But the industry was already in decline, as Richthofen observed:

The mining of coal, the manufacturing of iron, and the conveying of both to market employ a large number of men and animals. But notwithstanding its ample resources the country is poor. The profits are reduced to a minimum.  . . . Underground miners, who receive elsewhere 200 to 300 cash a day, must here content themselves with wages of 100 cash. Yet the owners of mines are poor people. There have evidently been better times in this region, as one is justified in concluding from the great number of houses built with luxury, and richly adorned with fine work of sculpture.

The competition with foreign trade is another cause of the decadence of the wealth of [this province]. If we commence with the trifling article of needles, their manufacture in Shansi has almost been annihilated, by the importation of the much better and cheaper foreign article. The same will be true, before long, in regards to guns and steel ware; and there can be no doubt that the injurious effects of foreign competition have been seriously felt by the iron trade of Shansi in general. Being the only noteworthy article of export from that province, the diminished sales and reduced prices contribute to impoverish the inhabitants. (Richthofen 1903: 31, 38)

By 1898 the production of iron in Shanxi had fallen to ca. 50,000 tons per year. It increased slightly during World War I, to 70,000 t/yr in 1916, but in 1950 it had fallen to less than 20,000 t/yr. Photographs in a pictorial magazine give a good impression of the industry in 1945 (Anon. 1945).

The iron and steel products of Shanxi were known for their high quality from very early times. The Tang and Song dynasty poets Du Fu 杜甫, Lu Lun 卢纶, Lu You 陆游, Zhou Bangyan 周邦彦, and Jiang Kui 姜夔 all mentioned the famous scissors of Shanxi. For many centuries a large proportion of the needles used in China also came from Shanxi.

In 1870 Richthofen gave great praise to the iron produced here, and in fact wrote that it was superior to European iron, but most later witnesses reported that Shanxi iron was quite inferior, containing far too much sulphur. Twelve samples analysed in 1911 showed between 0.13 and 0.64 percent sulphur (Read 1911: 27). Even the lowest of these values is higher than a smith would want, and it would for example be very difficult to make needles of this iron. In 1958, in connection with the Great Leap Forward, the process was considered unusable, and it was largely abandoned.

It is interesting that the crucible smelting technique was adopted in 1908 in Höganäs, Sweden, where it has the special advantage that it can use poor-quality Swedish coal, which cannot be used in a blast furnace. It seems quite certain that the ‘invention’ of the Höganäs process was directly inspired by the Shanxi process through the Swedish engineer Erik T. Nyström (Chinese name Xin Changfu 新常富), who taught chemistry and geology at Shanxi Imperial University in Taiyuan for many years from 1902.

Experiments at Höganäs showed that the sulphur content of the iron produced could be held down to 0.01–0.03 percent by the addition of a small amount of limestone (CaCO₃) to the crucible charge, combined with careful temperature control around 1200°C (Sieurin 1911: 458–459). It seems to be a reasonable assumption that iron producers in Shanxi had earlier used limestone in iron smelting, and stopped using it in order to reduce expenses. This is one of many examples of technological steps backward in 20th-century China in response to competition with cheap foreign iron.

Archaeological material related to crucibles

By Liu Peifeng 刘培峰

Translated by DBW

20 January 2022

Judging from presently available archaeological material, crucible smelting was widely practised as early as the Han period. For example, crucibles for iron smelting or casting were found at Western Han workshops at Qinghe 清河 in Beijing and Ershijiacun 二十家村 in Huhhot, Nei Mongol, and in a Han tomb at Jili Gongqu 吉利工区 in Luoyang. Especially significant are numerous ancient small iron-smelting crucibles, iron slag, ore, and ling 瓴 ceramic vessels found in Kuchar County 库车县, Xinjiang (location of the Han city of Kucha 龟兹). From the form of the ling vessels this site is dated to the Han period. Researchers consider that this site corresponds to the description in the 5th- or 6th-century book Shuijing zhu 水经注 of iron-smelting using mineral coal at Kucha [see Wagner 2008: 311].

He Tangkun has analyzed a piece of steel adhering to the inside of one of the Luoyang crucibles. It is hypereutectic steel with 1.21% carbon and 0.584% sulphur, and this corresponds well to modern Shanxi samples of crucible-smelted iron with 1.3% carbon. He Tangkun concludes that the technique of crucible smelting steel was known in the Han period.

Written sources and archaeological material (for example the foundry site at Kuding in the Yungang Grottoes area 云冈区石窟窟顶 in Shanxi) indicate that in north China in the Song period, because of a shortage of charcoal, the number of blast furnaces gradually decreased. In regions with concentrations of iron-smelting raw materials, especially in Shanxi, a large-scale crucible-smelting iron industry was established and continued into the 20th century.

Survey of crucible smelting sites in Shanxi

Wall of crucibles at Dijicheng in Yangcheng County 阳城县砥洎城, Shanxi. Photo by Fang Yibing 方一兵.	Beishe Ironworks site in Zezhou County 泽州县北社, Shanxi. Photo by Liu Peifeng.	Crucible iron-smelting site at Hougoucun in Gaoping Municipality 高平市后沟村, Shanxi. Photo by Liu Peifeng.	Sample of crucible iron. Photo by Liu Peifeng.

References

Last edited by DBW 25 February 2023