There are three main types of iron that should be considered: wrought, cast and steel.
Wrought Iron has a melting point of 1535 degrees C so it comes out of the furnace solid and is worked solid. It is hammered into shape and forms a tough finished product. It is good for tools and swords. It has less than 0.3 per cent carbon content.
Cast Iron comes out of the furnace molten and is poured into moulds to make its shape. It is brittle so it does not produce good tools or edged weapons. Often it is used for decorative objects. It has more than 2 per cent carbon. These two forms are dependent on the type of ore available, high-carbon ores will not make good wrought iron. Chinese ores, for example, are useful only for cast iron, which is why there is so much decorative Chinese ironwork.
Steel is a combination of iron and the right amount of carbon – between 0.3 and 2 percent – which makes it particularly tough and flexible. It is capable of holding an edge and is therefore very useful for tools and weapons. It is, however, very difficult to manufacture and involves “cooking” the iron and carbon together for many hours at more than 1100 degrees C.
The “Three Age” history of the introduction of iron in Europe is unique and not reflected anywhere else in the world. In southern Africa, for example, there never was a Bronze Age and the first metal to be used was iron. In North America native copper was hammered into shapes but was never smelted. In Europe the Iron Age followed the Bronze Age but there was no distinct line between the two. Iron was merely an additional metal. It is difficult to form into complex shapes, unlike bronze, and it corrodes easily so it was not a suitable material for all uses. By the 2nd millennium BCE a few iron items were in circulation, such as pins and awls but around 1100 BCE the metal took off in a big way. It appeared throughout the near east, Europe and Britain almost simultaneously.
There are two sources of iron – meteoric iron is extremely rare and can be identified by its high nickel content, iron ores are naturally occurring in the earth’s crust. Ores appear as oxides and sulphides; both are commonly available. Iron ore is rarely pure so there are almost always other constituents in any iron item. Unfortunately it is impossible to assign chemical “signatures” to European ores because they vary so much, so the inclusions are not useful for sourcing raw materials used in archaeological artefacts.
Thanks to Prof Elizabeth Slater (RIP), head of department at the University of Liverpool school of archaeology for clear lectures on artefacts and materials. J M Cronyn’s Elements of Archaeological Conservation has also been consulted.