Iron in China
|I don't know a thing about iron in China. I have never been there and seen anything
myself (e.g. in a museum) so all I can do is to summarize what I have read. Since Bennet
Bronsons's article1) is relatively recent and rather illuminating
(meaning it resonates with my own feelings or prejudices), most of what follows is based on his insights. We have met Bennet
Bronson before; he also wrote the still best review about the history
of wootz steel.
Otherwise it is always a good idea to consult the work of Donald B. Wagner, e.g. his book "Iron and steel in ancient China" (Leiden: Brill, 1993), and what Vincent E. Pigott has to say about that book. 3)
Many articles on ancient Chinese metallurgy appear to be heavily biased towards "China was always ahead by definition", and I have a problem with this kind of view. Here are some random examples from the Internet:
|First, "the Warring States period is a period in ancient China following the Spring and Autumn period (771 BC - 476 BC) and concluding with the victory of the state of Qin in 221 BC, creating a unified China under the Qin Dynasty." says Wikipedia. Second, wrought iron casting techniques and so on are certainly impressive, in particular because they are oxymorons, i.e. contradictions in terms.
|Maybe they did use coal as early as the 4th century AD, maybe they didn't (its disputed). Whenever they did it, they also made sure that they had all the phosphorous and sulfur problems coming with this "superior" technology. Easy casting of doubtful stuff - yes. Good steel - rather not!.
|A "cast - wrought" sword? Made from cast-iron, iron or steel? 200 BC is early? Compare to much older Luristan swords or somewhat older Celtic swords. The "folded hundred times steel" method presumably is a good thing? No - it simply tells us that the iron / steel used for sword forging was extremely inhomogeneous.
|And so on ad infinitum or nauseatum.
I'm not saying that China isn't a very old culture that was superior to others in some aspects of civilization and technology some of the time. Be that as it may, as far as metal technologies in general, and iron technology in particular was concerned, they weren't all-out superior, they just were very different.
The art of making metals including iron actually arrived (or was discovered) rather late in China. That is also true for copper and bronze, but in particular for iron. After iron smelting was started, however, it developed very quickly and in a peculiar way. The Chinese, it appears, made almost exclusively cast iron in what one would call a blast furnace nowadays, essentially skipping the making of wrought iron in "bloomeries".
Steel was made by "fining", i.e. taking the carbon out of the cast iron by burning it off in air. That is the principle of steel-making today. The early Chinese techniques included a kind of puddling" process, which is similar to processes used in the West much later (let's say after 1500 AD). Does that mean that the Chinese were 1000 years or so ahead of the West? It's a matter if definition. If you prefer a bad steel made by an advanced method to good steel made in an old-fashioned way, the Chinese were ahead.
|Of course, iron objects from before 200 BC have also been found - just not very many. In a country the size of China, this simply must be expected. Some meteoric iron might have been used or the occasional bloomery might have produced some iron. I won't go into this because pretty much everything is disputed. The fact is that iron and steel technology only made a difference to people in general after, roughly, 400 BC. Even then, up to about the beginning of the Christian age, bronze objects (tools, weapons, adornments, ...) far outnumbered iron objects as grave goods. Iron objects were mostly found in garbage dumps. That doesn't necessarily mean that iron was cheap everyday stuff but that its use was mostly practical and not ceremonial / decorative. The kind of emotional attachment you entertain for your trusty and beautiful sword will usually not carry over to your rusty and broken shovel blade.
|By 200 BC a large iron industry was in place, run by wealthy clans or the state.
It was well-organized and thoroughly controlled. The primary product was cast iron, feeding a large and sophisticated secondary
industry. Integrated "plants" ran, for example, "8 blast furnaces, 1 fining hearth for puddling, 1 annealing
furnace for solid-state de-carburizing, 11 mold baking furnaces or kilns, 5 general purpose heating furnaces and 1 forge".
I'm not sure if that beats what the Romans did in their "factories" around this time, but it is certainly impressive.
But only 1 forge? That indicates that the vast majority of the cast iron produced was indeed cast into molds for making tools (like digging implements), pots and anything else that can be made from brittle cast iron. Don't make the mistake of conisdering brittle = weak, useless, not strong. Your toilet is made from brittle material but easily takes your weight and other abuse for long times.
Steel making by "fining" or "puddling" the cast iron, followed by forging the steel, was not only a laborious process but could not have produced high-grade steel easily.
|The Chinese cast-iron industry certainly pre-dates "ours" by 1 500
years or so. The reason, however, is not that the Romans or others in the West couldn't make cast iron! They could, in fact,
but they didn't want to! They simply had no use for the brittle stuff.
The Chinese, to their everlasting credit, used their cast iron for making peaceful objects, including flower vases and (huge) sculptures. Western cast iron, when it was finally produced, went immediately into cannon making. So the Chinese certainly take the price for being the good guys. Our ancestors were the bad guys by comparison. That might be morally questionable but has its advantages. They easily conquered and subdued the good guys with their superior iron / steel weapons. Look up what the British did in the so-called "opium wars". Of course, nowadays they are really sorry for that, and acknowledge that the Chinese had the moral superiority then. (Haha, good joke, huh?). Some of our German (good) guys around this time wrote the music that the Chinese (and everybody else on this planet) like to listen to ever since, by the way.
While the Chinese cast-iron industry was far ahead of the rest of the world around 200 BC, there is also another side to this: The technology hardly changed during the next 2 000 years or so. Here are pictures from smelting cast iron and "puddling" steel from 1958:
|Now look at how that was done around 1600 and quite likely also 1800 years earlier.
|Note the "bellows", operating on the principle of a bicycle pump, and delivering air in both strokes, in and out. That was rather advanced in comparison to a single-stroke accordion bellows.
|Of course, making steel can't be done exactly like shown here. Liquid cast iron
kept in a square pool as shown above would solidify far too quickly, not allowing the removal of a large part of the carbon
by reacting with the oxygen from the air. Well, as one of the top experts on Chinese Iron History, Donald B. Wagner remarks:
"The description and illustration are so precise that there is no real doubt that Song Yingxing, or the author of his source, had seen something very like this process. But it is very difficult to explain. Anyone who has worked with molten cast iron, as I have, will immediately object that the cast iron from the blast furnace, flowing into such a large open hearth, without thermal insulation, fuel, or any sort of air blast, will solidify before any significant amount of carbon has been removed.
Most translators and commentators seem unaware of this objection. They explain the passage and illustration in terms of modern open-hearth steelmaking processes, and state that the curious "wuchaoni" (some sort of earth used in the process) would contain iron oxide, FeO, to help remove carbon by the reaction FeO + C = Fe + CO, but this would not solve the problem.
The only commentator, as far as I know, who has been aware of the problem was one of the first, the German metallurgist Adolph Ledebur, more than a century ago, and he also proposed a solution. A Japanese friend had shown him a copy of Tian gong kai wu and translated the metallurgical sections for him. In his article about it he suggests that the wuchaoni spread on the iron contained saltpetre (potassium nitrate, KNO3). It is a powerful oxidizing agent (this is its function in gunpowder), and might very well be able to accelerate the oxidization of the carbon in the iron sufficiently to keep the temperature up until the carbon is exhausted and the cast iron has been converted to wrought iron."
|Be that as it may, one thing is quite clear. You may get de-carburized iron this way - but certainly not very good steel .
|There is a bigger mystery, however, than exactly how the puddling process worked:
How could the old Chinese furnaces produce cast iron? It's not so much a question of the temperature but of the chemistry
inside a furnace. Eutectic cast iron at 4.3 wt% carbon melts at a mere 1130 oC (2066 oF), easily achieved
in any kind of charcoal-run furnace with some air blown in. The problem is to get the carbon inside the pure
iron that is initially produced by a solid-state process at this temperature.
It's a matter of creating a "self-amplifying" process. You must allow enough time at temperature as high as possible in the reduction zone in your smelter, so that iron + carbon monoxide succeed to move enough carbon into the still solid iron in order to decrease the melting point to a temperature where the steel thus produced becomes liquid. The liquid stuff then can dissolve carbon easily and stay liquid even at the lower-down parts of the furnace, where it might be colder.
|Nothing helps: your furnace must get very hot, far hotter than a normal bloomery producing
wrought iron. It was clear how to do that - to the Chinese and to their counterparts
in the West: Increase the charcoal to ore ratio and supply more air. The Chinese smelters had double-action "bellows"
(actually more a kind of air-pump akin to what you know from your bicycle) that provided a continuous airstream at the forward
and the backstroke of the pistons, so they might have had an advantage in the air supply
department. The price to pay for that is money. Your costs go up - more manual labor and more charcoal compared to making
solid iron in a bloomery.
It essentially boils down to the simple question: do you want to make cast iron? The Chines said: yes, the West said: no.
|Bennet Bronson: "The transition to iron in ancient China" in "The Archeometallurgy of the Asian Old World", editor V.C. Pigott, Uni. Museum Monograph 89; University of Pennsylvania, 1999
|D. B. Wagner, "Iron production in three Ming texts" Third International Symposium on Ancient Chinese Texts and Records on Science and Technology, Tübingen, 31 March - 3 April, 2003.
|Vincent E. Pigott: "The Study of Ancient Metallurgical Technology; A Review", Asian Perspectives, Vol. 35, No.1 (1996) p-89
History of Carbon
Diffusion in Iron
10.1.3 Smelting, Melting, Casting and Alloying Copper - The First
10.5. Iron and Steel in "Modern" Europe. 10.5.1 From Bloomeries via Stückofen and Catalan Forge to the Blast Furnace
Critical Museum Guide: Metropolitan Museum, NYC
Critical Museum Guide: Landesmuseum Württemberg; Württemberg State Museum, Stuttgart, Germany
10.2 Making Iron 10.2.1 Early Iron
10.1.1 Discovering Metals and Smelting
Steel Revolution. 1. The Kelly - Bessemer Process
Smelting Science - 1. Furnaces
Early Pyrotechnolgy - Pottery
10.2.3 Smelting Wrought Iron, Steel and Cast Iron
11.3.2 More to Pattern Welding
11.6.4 Metallurgy of the Japanese Sword
Smelting Science - 5. Smelting Details 2
10.1.3 Smelting, Melting, Casting and Alloying Copper - The Second
Antique Texts Concerning Crucible Steel
10.5.2 Making Steel up to 1870
Iron in Africa
11.6 Japanese Swords 1.6.1 The Myth and the History of the Japanese Sword
10.4. Crucible Steel 10.4.1 The Making of Crucible Steel in Antiquity
Tricks of Smiths
Riveting, Soldering, Liquid Welding Plus Gluing and Screwing
Cast Iron; 9.5.1 General Remarks
Smelting Science - 5. Smelting Details 2
Hardware Around the Making of Metals and Their Proper Names
Science of Deformation
Fracture Mechanics II
Smelting Science - 4. Smelting Details 1
© H. Föll (Iron, Steel and Swords script)