A grave chamber from Austria around 400 BCE contained a shield with lots of thin iron reinforcements. It had engraved iron sheet over the wooden 'barleycorn' boss, four legs with curled 'antennae' ends, and reinforcements along the rim. It would have looked something like this (although this is from a different grave near the same village).
Currently the iron reinforcements are only about 0.15 to 0.20 mm thick (I think that would be around 32 gauge brass). How feasible would it be to forge iron or steel that thin? The Romans loved thin sheet brass like that, but copper does not oxidize quite as fast in the fire (and it does not have all that slag that can cause it to split).
I have never done hot metalwork, except maybe pumping someone's bellows or soldering electronics in school.
Here is the reconstruction of the Dürrnberg grave 373 shield. The article does not have many measurements and the diagram is scaled "1/4 life size" not "this much = 1 cm" but they seem to think that the spina and umbo were something like 60-70 cm long.
They seem to have made these the lazy way with two separate plates covering the left and right of the umbo with a 'gutter' placed on top of the place where the two plates butt together like the ridge of a tile roof.
You would need good hammerwork to make such thin sheet by hand.
There would be two ways to make thin sheet. Worked hot, with large amounts of scale being formed and reducing the overall size of sheet. Cold working with frequent annealing, with scale loss reduced. This will be dictated by quality of iron billet and its slag content and chemical composition and the tendency for the iron to split?
One variable which i don't think you can tell is how much was it ground/polished after forging? Did they forget to 2mm thick and grind down or forge to 0.7mm and grind down to 0.5mm?
Andrew
Andrew Bodley wrote: ↑Sat Nov 25, 2023 7:12 am
There would be two ways to make thin sheet. Worked hot, with large amounts of scale being formed and reducing the overall size of sheet. Cold working with frequent annealing, with scale loss reduced. This will be dictated by quality of iron billet and its slag content and chemical composition and the tendency for the iron to split?
One variable which i don't think you can tell is how much was it ground/polished after forging? Did they forget to 2mm thick and grind down or forge to 0.7mm and grind down to 0.5mm?
Andrew
Once you have a thin sheet (say a bit under 1 mm), cold work seems like a good way to get the thickness down without burning up too much of the iron.
My instinct is that in the Iron Age, workers did not remove a lot of material by grinding, because they didn't have watermills and may not even have had oxmills like in the Roman empire. People sometimes speculate about rolled sheet steel in the Roman empire, but 400 BCE is just about the time when cranks were invented in Spain, and there were about two towns in all of barbarian Europe. So if you wanted to polish something, you probably tied it down and went over it by hand.
