I’ve been doing some reading in an attempt to wrap up my piece on iron smelting chemistry and processes, and I was thinking about why iron is such an interesting subject to study.

I think it probably comes down to the juxtaposition between incredible utility and practicality of the metal, and the sheer difficulty and technical sophistication needed to produce the metal and really develop the best of its properties.It’s simultaneously extremely functional and actually quite expensive and in some cases status bearing.

Iron itself is a strong, hard, flexible and above all workable metal that can be given an extremely sharp edge. As a material it had no comparison during the pre-medieval period. In general it hits western Europe by 1000 BC at its earliest, often becoming practically common place for objects such as swords by around 400 BC and then extremely common for use in a dizzying array of uses by the Roman period (around 100 BC into AD 100).

Without iron, there would be no large buildings, either. Cathedrals and castles are all held together using iron clamps, so were many of the ancient buildings like the Parthenon and the Pantheon. Even smaller buildings and wooden fortifications would hardly have been possible without iron nails. As soon as we could, we used iron to make almost any conceivable thing, because it was harder and sharper and just plain better.

But one of the most intriguing things is that all the complex processes necessary to produce iron, select or control for additives like carbon or phosphorous, and then work the iron at various extremes of heat and cold to change and alter the internal crystal structures and hence achieve the desired properties, all of these were done by practitioners with no actual knowledge of these unseen things.

They didn’t know how much carbon or phosphorous was in the iron – they knew what ores and processes they were using and how these effected the working properties of the iron. They couldn’t see the crystal structures of the metal bar and note how they were changing them during smithing, they could only judge by colour and deformation, practice and experience.

Ancient practitioners had to rely on empirical evidence, rather than any theoretical structures. They couldn’t explain why things changed they way they did, but they had to understand them through physical experience. Some of the processes they undertook had very narrow limits within which they had to keep, or the process would fail. So narrow that I wonder how they could have judged them at all sometimes. How amazing is that?

Another interesting fact about iron, is that the ores are available almost anywhere. No one could control iron production, once knowledge of how to do it was readily available. The knowledge of copper smelting appears to have been reasonably widespread, and the basic processes are the same.

Although most iron was first introduced as an import, once people got the knowledge of how to smelt it, it spreads all over the place. It’s really a rather democratic activity in western Europe, something that doesn’t seem to have been controlled in most countries.

I can find slag from production or smithing on almost any Roman site in Britain. How cool is that? People were making or working this incredibly useful metal all over the place, in their homes, in villas, in cities and towns and legionary camps. I suspect that all kinds of people from all over the world and in all kinds of contexts had the knowledge to either produce or work iron, and I think that makes it a really exciting thing to study, particularly in the Roman period.

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