Donald B. Wagner, Background to the Great Leap Forward in Iron and Steel
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Chinese iron-production technology
|Process diagram for iron production in a traditional Chinese ironworks.|
Around 1600 the Chinese iron industry was the world’s
largest and most efficient, and had been so for 2000
years. The great difference from the rest of the world lay
in the use of the blast
furnace, which was invented in China by the 3rd
century BC. In Europe the first blast furnaces were
introduced (possibly from China via Iran) in the 12th
century AD, and it was not
|On bloomery iron smelting see especially Radomír Pleiner, Iron in archaeology: The European bloomery smelters, Praha: Archeologický Ústav Avčr, 2000; see also numerous demonstrations of the technology on youtube.|
until the 16th or 17th century that the blast furnace largely replaced the bloomery and became the dominant iron-smelting technology.
The diagram above shows the most important processes in a
blast-furnace ironworks. This is called indirect iron
smelting, because the blast furnace produces cast iron
(also called ‘pig iron’) with 4 percent carbon, and this
carbon is then removed to make wrought iron. Iron
production in a bloomery, on the other hand, is called direct because wrought
iron with a low carbon content is produced in a single
A technical description of the operation of a blast furnace can be seen here. Briefly, a blast furnace is charged with iron ore, fuel (charcoal or coke), and normally a flux (usually limestone), and produces molten iron with ca. 4 percent carbon in a process which continues day and night for long periods: in modern times, years, in older times, weeks or months.
|On cast iron
see my ‘Cast iron in
China and Europe’.
Iron from the blast furnace, with high carbon content and relatively low melting point (as low as 1150°C), is cast iron. This can be used directly by an iron foundry, but it is brittle and cannot be worked by a smith. To obtain wrought iron, with low carbon content (and therefore high melting point, over 1500°C), the carbon must be removed, entirely or in part. This has been done in numerous ways: in Europe the earliest process was fining; in the 18th century puddling was introduced, in the 19th century the Bessemer process, and in modern practice numerous other processes.
|Fining of cast iron to wrought iron in Shanxi, 1958. (Rewi Alley, China’s hinterland—in the leap forward, Peking 1961).|
Common to all the traditional Chinese processes for conversion of cast iron to wrought iron is that pieces of cast iron are heated to a very high temperature (1200–1500°C) and stirred about in an oxidizing atmosphere. If the worker is skilled at his job the carbon is burned out of the iron without too much of the iron being burned. All of the variants of this process used in China are called in Chinese chao 炒, a word whose basic meaning is ‘stir-frying’; numerous Chinese metallurgical terms come from the kitchen. In English I call the processes either ‘fining’ or ‘puddling’, depending on which of the two European processes they most resemble.
For technical reasons which are sketched here, the blast furnace
gives enormous economies of scale: the greater the
production the cheaper the iron produced. A general rule
is that for maximum efficiency a blast furnace should be
as large as the supply of its raw materials and labour,
and the market for its production, will reliably allow. No
larger than that, for efficiency also requires that the
furnace operate continually for years at a time; the cost
of interruption of operation caused by labour or raw
materials shortages, or by a failure of the demand for pig
iron, will quickly eat up the intended economies of scale.
Iron ores and the fuel needed for smelting are found
nearly everywhere in the world in quantities sufficient
for pre-modern production levels, and iron is relatively
cheap by weight. These two facts mean that transportation
costs are an extremely important factor in the geography
of pre-modern iron production. In Europe, until late
medieval times, iron was most often a local product, and
only especially high-quality grades were traded over long
distances. The situation was rather different in China.
The higher efficiency of large-scale blast-furnace iron
production meant that transport costs played a smaller
role, and it was profitable to produce for larger markets.
Larger markes meant, however, that competition between
producers was intense and profits correspondingly low.
Iron production therefore most often took place where the
resources required for more profitable activities were
lacking – where the comparative advantage
was in iron production. This was generally in the poorest
regions of China.
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