Posts by Professor Woozle

Find pushes back birth of Europe's steel hardware to about 3,000 years ago

Re: People move around shocker !

I disagree about local production being the most likely explanation and this is why. What we see with the emergence of iron on the Atlantic seaboard in the LBA is artefacts that are not only made of iron, but also include steel that's been quenched and tempered. There are several technological leaps here from bronze working, all of which were by that time well established in the eastern Mediterranean and Anatolia. Bronze was still in widespread use, so copper and tin deposits like those in Britain/Ireland and Spain were being worked and traded into the Mediterranean. If you have traders from either place going to the other, or a chain of trade going on, then would you not likely see the new "wonder metal" being traded westwards as the copper and tin was traded east?

There will have been a point where iron and steel making did start on the Atlantic seaboard, but... first of all, you have the difference in bloomery iron making that what comes out of the furnance is not a castable liquid, but a grotty-looking sponge of iron and slag, that you then need to keep heating and beating until most of the slag has gone and you have a bar of iron you can make something out of. Secondly, you have to know that some bits of this iron are harder than others, and if you take those, drop them into water while they're red hot, then gently re-heat them until certain colours show, you get something that's a lot harder than regular iron but doesn't shatter (which it will if you hit it straight after dropping it into water). Finally, you need to be able to forge-weld that harder stuff onto regular iron, and there's a very narrow temperature range just below white hot at which that can be done otherwise your precious hard stuff turns into a sparkler and burns away, or the weld doesn't take and the cutting edge falls off your tool/weapon when you try to use it.

Given all of that, for the very earliest iron artefacts on the western fringes of Europe which show that they were steeled and quenched and tempered, I think there are rather fewer assumptions involed in them having been traded in.

Re: The practicalities and science of steelmaking ( was - People move around shocker ! )

I can see why we're at odds over this now, which is a good start! What you were taught isn't wrong, but it's really only applicable to post-19th century steel production. There have been two major technological shifts (in European steelmaking) since antiquity, firstly the move away from the bloomery furnace to the blast furnance in the 16th and 17th centuries, and secondly the move towards alloyed steels from the mid-19th century onwards as improved scientific analysis gave rise to steels that were optimised for particular jobs.

However, steel is in its strict definition, the alloy of iron and carbon and if other elements are there by design, then it's an alloy steel. Although some steels in the past did have trace elements in them (Wootz, for example has a small amount of Vanadium in it, which does some interesting things with the crystal structure), it wasn't intentional, it was a by-product of the ore used.

The hotter temperature of blast furnances does change what goes into the iron and what goes into the slag; some silicon can get into blast furnace iron while the use of limestone is to improve the yield by providing calcium to preferentially combine with the silicon and go into the slag. In bloomery smelting, the temperature isn't high enough for that and instead, any silicon combines with some of the iron to form a liquid iron silicate slag. That's part of the reason for the adoption of the blast furnace over the bloomery, in that you recovered more of the iron from your ore; you could also resmelt bloomery slag and recover the iron from that.

As for Sulphur, yes it's something you don't want in iron as it causes embrittlement at high temperatures, and it falls into bits when you try and forge it! That's why charcoal was generally used for smelting and smithing until the industrial revolution as any Sulphur present in the wood it was made from tends to disappear as Sulphur Dioxide during the charcoal burning process. There are some places where coal was used in antiquity, but those are places that happened to have easily-dug sources of coal with minimal Sulphur content. It wasn't until the coking process was perfected (basically doing the same thing as you do to wood in charcoal making, burning it just enough to get rid of unwanted impurities and leaving mostly carbon) that fossil-fuel based iron and steelmaking took off, as it freed the ironmasters from the constraint of available sources of wood to make charcoal from. Although it's often repeated that ironmakers were responsible for destroying a lot of woodland, the reverse is true - while charcoal was needed, they were buying or renting woodlands to secure their fuel supply, the shift to coke made the woods less valuable and prompted landowners to clear them and turn the land over to agriculture where that was viable.

The practicalities and science of steelmaking ( was - Re: People move around shocker ! )

Sorry, but that's not the case - in a bloomery furnace, what determines the carbon content of the raw iron produced (the bloom) is the level of excess of carbon monoxide over and above that required to react with the iron oxide to form carbon dioxide and iron. If you increase the rate of air flow and the amount of fuel going in, you will raise the temperature and amount of carbon monoxide in the reaction zone to the point where enough carbon has gone into the iron to lower its melting point to the furnance temperature, resulting in cast iron - not steel, note, but cast iron which is higher in carbon and brittle. The critical temperature at which carbon can begin to diffuse into iron is a little over 700 degrees C, where the crystal structure of iron changes (the Austenitic point) - the rate of diffusion will increase as the temperature gets higher, until eventually you hit the point where the increased carbon content has lowered the melting point of the iron to the ambient temperature of the furnance, and you get cast iron instead of hypereutectoid steel.

There are three routes to getting a steel with a carbon content suitable for making tools and weapons (generally 0.5 to 1%). Firstly, there's direct production in the bloomery furnance by using a higher fuel to ore ratio, which produces steel in the solid state without it being molten - a good example of this is the traditional Japanese smelting process, where the blooms would include both softer iron and harder steel and the smelters/smiths could recognise which was which. Secondly, there's cementation, where bars of iron are packed into a sealed container with charcoal and heated for an extended period - the Wootz process is an example of this, though they got the furnance hot enough that the resultant steel melted within its sealed container. Thirdly, there's decarburisation, where molten cast iron has a blast of air put through or over it to burn out the carbon until it reaches the desired content - the Bessemer converter is the classic example of this, but there's evidence that suggests tool steels may have been made in antiquity by decarburising cast iron.

Steelmaking technology was it seems widely known in antiquity, going by the amount that's been found. Given it was an expensive (and recyclable) material, it's quite likely under-represented in the archaeological record as it was always more expensive than regular wrought iron (which in turn wasn't a cheap commodity in the past), and so would have been more likely to get re-used. From what's known from historical writings, there probably was a strong element of craft secret and "do this thing that grandad told us to" about it, but around the world, every iron-using culture seems to have had some way of making "the tough stuff" and working it into a usable tool or weapon.

As for blast furnaces, they're pretty much the same as a bloomery furnace being at the core a shaft built out of refractory material with a source of air blast at the base and an open top where you put the ore and fuel in. The only real difference is that the blast furnace has a stronger blast of air going in (hence its name), burning more fuel to given the conditions that will result in molten iron.

I'll give you one guess what I did my dissertation on at university all those years ago...

Re: People move around shocker !

Sorry, but that's not the case - you do not need a blast furnace to produce steel, all it needs is a higher charcoal to ore ratio in a simple smelting hearth so there's more carbon monoxide available in the reducing zone to go into the iron, and the iron ore to not contain certain impurities, principally phosphorus.

The finding of this paper is also not as ground-breaking as they're making out, IIRC (from my university days three decades ago) the earliest dated iron artefacts in the British Isles (of similar date to these Iberian ones) had steel cutting edges that had been welded on to a softer iron back, and they had also been quenched and tempered to give the edge the optimum combination of hardness and toughness as a working tool. What it's showing is that when the technology of iron and steel working reached the western edges of Europe, it was a mature technology. What's harder to tell is whether objects being made elsewhere were traded in, craftsmen from areas where the technology was already established were moving in, or local craftsmen were acquiring the knowledge. Given we're actually talking about a range of some centuries, a combination of all of the above is entirely possible, and all of them are difficult (though not impossible) to definitively evidence in the archaeological record.