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Rolling Roman Iron for Segmentata Plates
#1
I found the article previously referred to regarding the posibility that Roman blacksmiths used rolling as a technique for elongating or flattering iron into strips or sheet.

I purchased a copy of the article from one of the online resources. $30... well worth it.

Article Source:
Journal of Archaeological Science 32 (2005) 241–250
In defence of Rome: a metallographic investigation
of Roman ferrous armour from Northern Britain
by Michael Fulford, David Sim, Alistair Doig, Jon Painter

From Table 1 Summary of Metallographic Observations
From the column labeld "Comments" the reference to rolling is:
"straight line interfaces,
so large hammer used
or rolled"

And another reference in the text of "Fig. 4. Photomicrographs of Vindolanda armour (Nos. 6–7). Vindolanda Lorica No. 7"
"1 further along at higher magnification (smaller grains) very clean iron straight interface so colled rolled end face?"

"....the Vindolanda fragment
was found in 1992 on the floor of a room in what was
probably a barrack building of Period IV date, c. AD
105–20 (pers. com. R. Birley)."

The Vindolanda segmentata fragment was of two layers of what has been interpreted to be... forge welded iron... Yup, 2 layers!

(On a personal side note this solves my problem regarding the iron I have, that I'm using to make an iron segmentata.. I do not have enough iron that is voluminous enough to forge out plates to be as wide as they need to be and as thick.. forge welding two thinner plates solves that dilemma!)

The text of the article contains no references to rolling.

In Iron for the Eagles The Iron Industry of Roman Britain by David Sim and Isabel Ridge, 2002, the idea of rolling is suggested as a possibility, page 950-96... "A system of rolling used in the production of olive oil was well known in antiquity, and it is therefore that a similar system may have been used to make sheet iron. However, it has to be noted that at present there is no specific evidence to support the use of rollers by the Romans."

Then here on RAT in the thread: "Wikipedia lorica segmentata article", Mike Bishop teases us with: "The evidence is mounting that billets were not the raw material from which armourers worked and that plate (possibly rolled) was available to them. "

The evidence for rolling is derived from the way the sheet iron looks (examination by enlarged cross section), suggesting rolling as one possible method of forming.

According to Mike Bishop, the next JRMES wil contain an article by David Sim about scale armor.... But, I say, " Hey what about segmentata??"

I have some questions ...

Cold rolling iron at what pressures to produce sheet?
Could the same results be achieved using something like an English Wheel? If so then a large and/or weighty wheel would be unnecessary.
What about using some sort of mechanical hammer.. a form of trip hammer? It doesn't need to be water driven.
Could a treddle hammer work to achiece the observed results?

How extensive is the evidence across regions and time for rolling as a technique for producing sheet iron?

Is hammering the more common technique?
Hibernicus

LEGIO IX HISPANA, USA

You cannot dig ditches in a toga!

[url:194jujcw]http://www.legio-ix-hispana.org[/url]
A nationwide club with chapters across N America
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#2
Quote:I have some questions ...

Cold rolling iron at what pressures to produce sheet?
Could the same results be achieved using something like an English Wheel? If so then a large and/or weighty wheel would be unnecessary.
What about using some sort of mechanical hammer.. a form of trip hammer? It doesn't need to be water driven.
Could a treddle hammer work to achiece the observed results?

How extensive is the evidence across regions and time for rolling as a technique for producing sheet iron?

Is hammering the more common technique?

All seem quite reasonable possibilities to me Sean- I particularly like the idea of an English Wheel type of rolling system for working individual plates to a uniform thickness and smooth faces.

The thing is though, it requires photomicrographic analysis of thin sections to get a good idea from the crystalline structure just what method(s) of making a particular object were likely used. Unfortunately, I'm not sure any other studies like this one have ever been done, so there may not be any other real evidence for methodologies around as of yet. So I'd expect the answer to your question about how 'extensive' the evidence (of any method) is: it's not.

What I took away from the article was that there were quite a few methods and techniques in use- probably contemperaneously- and that rolling could well have been one of them.
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#3
Sim has done some extensive research.... I believe that Beyond the Bloom, 1998, was based on his Doctoral Thesis. In it he seems to hint at rolling as a possibility.

The pressure needed to cold roll bar into sheet is high.

Could the Romans produce enough pressure to cold roll hand hammered sheet to thin it further inorder to harden it AND cause the effects he notes in the "grain" of the iron he's studied?

Conversations with others, in the past... that simpler methods for further shaping thin hand hammered (flattered) sheet say via a tool similar to an English wheel will not likely produce the "grain" Sim uses for his evidence of the possibility of rolling. Hand hammering does. It is possible that annealed sheet iron might show miscrosopic evidence of rolling in a tool like an English wheel.

I mention an English wheel because it is relatively simple to make and use. Its primary use is to put a curve into metal,(compound curves too!) by pressing the sheet between two wheels under pressure, one wheel being larger than the other. If the two wheels are essentially the same size you can elongate sheet.

It's frustrating.. I can get iron, have a load of it in the workshop, made some pilum from it! Making that seg and forge welding will now make it possible for me to finish it.

I'm not sure Sim can do more than say that rolling was a possibility... or that rolling was the likely method for fashioning the particuular sheet iron he studied. We'll see. Hurry up JRMES!!!

Mike, how about a preview???
Hibernicus

LEGIO IX HISPANA, USA

You cannot dig ditches in a toga!

[url:194jujcw]http://www.legio-ix-hispana.org[/url]
A nationwide club with chapters across N America
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#4
Someone wrote me direct and asked if I'd chainged my opinion.. nope.... I'm still of the opinion that hammering was the likely method for making sheet iron and not rolling which means that we'll continue hammering out CR steel plates to achieve the desired result.
Hibernicus

LEGIO IX HISPANA, USA

You cannot dig ditches in a toga!

[url:194jujcw]http://www.legio-ix-hispana.org[/url]
A nationwide club with chapters across N America
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#5
It's important to be careful and remember that the idea of 'THE method' is wrong- the one thing we should all recognize by now is that there were many methods in use at any given time for making or doing just about anything. Just as is the case with respect to uniformity, consistency of production is a modern idea- completely inappropriate to apply to ancient times. Clearly the article I mentioned shows that each piece examined shows evidence of different material/ methods of manufacture- forge welding, hot working, cold working, decarburisation, iron, steel, possible rolling, etc. Sadly with such a tiny sample having been examined, not much in the way of artifactual evidence to back up any method particularly well, we're left with mainly supposition. And that's a very dodgy thing indeed.

Sure, hammer forging to make plate seems a reasonable possibility- it's clearly the easiest method, however it's not exactly the most efficient, and it's a little difficult to imagine so many smiths getting the even thickness plate that it seems Roman armor had. Rolling would achieve this but there's only circumstantial evidence to support its use- no artifacts or direct mention by a literary source are known.

Looking at copper alloy pieces, however, one sees a remarkable smoothness and evenness to the metal that begs the idea of something a little more than just a hammer. It's not easy to achieve even thickness of very thin metal by hammering, and virtually all the copper alloy artifacts in my collection seems quite uniform and clean. No hammermarks, no rippling and an even thickness is what I see in almost every piece. In addition, the shallow incised lines along the edges of some forms of segmentata fittings are so nicely-placed and even that anything other than a roller-type machine to make them seems hard to believe. It was these observations that first made me wonder about rolling to produce sheet metal- or rather, to finish sheet metal- no one is suggesting that rolling was a single method of producing sheet metal from ingots Sean- doubtless it was forged quite a bit until it would have been thin enough to roll (if in fact it was). However that hammering need have been only 'quick and dirty'.

A rolling mill is a fairly simple, hand-operated device that is widely available today for producing a desired thickness of sheet metal and wire, and it would have been well within the technological abilities of the Romans. Pressure isn't applied per se- it's built into the machine by virtue of the proximity of the rollers. Modern rolling mills are adjustable so one can gradually thin out metal by decreasing the roller separation on subsequent passes, however there's no reason several dedicated thickness mills couldn't have been used to achieve this. A Roman one could have been quite a small machine too- remember the widest plate of a segmentata was actually quite narrow, no more than 9.5cm for a Corbridge cuirass. A strong frame, a good long crank arm for leverage- it'd be an easy machine to operate for any completely unskilled person.

Doubtless hammering a method used to produce iron plate for armor- but was it the only one? I find that hard to believe. I even have my doubts that it was the main one given how much more efficient and effective rolling is. The Romans were clever and had some impressive technology for the time- it's a mistake to just assume they wouldn't have developed and used a device as simple as a rolling mill given the sheer volume of sheet metal they used. Of course it's also a mistake to assume just because they had some great technology that they must have also had rolling mills- assumptions with no direct evidence of anything are hazardous to say the least :wink: We therefore can't say any method is right out or far more 'correct' than another without a whole lot more evidence. So for now, I think it's fair to say that hammered steel is just as acceptable for reproductions as rolled is Big Grin

As a related aside- does anyone know what methods for producing sheet steel were in use during medieval times or the renaissance? Neither, it seems to me, were radically more technologically advanced than Roman times so might shed some light on things.
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#6
Compresing through rolling is surely not like inventing a steam engine. My grandmothers doing the washing in a mangle when I was five years old could tell you that.

Given that there were specifications for spathae, according to one lanciarius in his found letters, why wouldn't there be for armour? Forget frontier remoteness; if word had gotten around about this fantastic armour then I dare say the local legion commanders would facilitate finding out how through their many connections, and gladly share it with the local fabricae, if only to shut up the grumbling legionaries and auxilia who wanted to import the stuff from abroad.

Or rather, I can really imagine that.
TARBICvS/Jim Bowers
A A A DESEDO DESEDO!
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#7
It would be nice to be able to say that Romans definitely had rolling mills - uniform thickness of plate suggests it is a possibility - but no positive archaeological evidence either way. Same would be the case for any big chunky press or machine hammering system. We do have evidence of major industrial complexes (Manchester, Wilderspool & Templeborough included) but not a lot of archaeological evidence (Templeborough was trashed in a big hurry for Sheffield's steel industry & the excavs by T May were rescue, just ahead of the builders - literally).
Another aspect here is that Sim is still trying to replicate the quality of Roman iron using charcoal as fuel, and has not yet factored in the effects of using coal as fuel, despite the major coal & iron exploitation of this country by Romans. This also has implications for the type of iron you ought to use for your experimentation if you are attempting to be 100% authentic (which will never be achievable anyway for a whole mountain of other reasons).

Just tapping the top of the iceberg here

Hilary
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#8
Where did I read that something like a fifth of the volume of olive oil generates as much or more heat than charcoal? Probably not relevant anyway.
TARBICvS/Jim Bowers
A A A DESEDO DESEDO!
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#9
Would that be controllable though? I mean as far as using the olive oil as a heat source...would it last as long? I wonder what it would add molecularly (molecularily?) to the structure of the iron, since the charcoal adds carbon thus making steel.
____________________________________________________________
Magnus/Matt
Du Courage Viens La Verité

Legion: TBD
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#10
Yes olive oil would burn, same as charcoal burns, but coal gives a more controllable burn, with a steady temperature. Charocal may be used combined, to initiate the burn, but there are many types of coal available, some of which are quite well suited to metal working and even smelting. These also occur naturally in the same locations as the ironstone and are found on many archaeological sites, although often not recorded (or recorded as charcoal in error).
The steady heat produced by coal could produce metal consistent with the samples reviewed by Sim.

Hilary Travis
(slight theft of intellectual property here, but with permission - subject of many years research of my husband's Phd)
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#11
That may simply be a comment on the energy content and density Jim- the same kind of thing as the fact that alcohol (ethanol) contains more energy, biologically-speaking, than does sugar (glucose). The statement is 'per unit VOLUME'- coal is porous, olive oil is liquid, so there's a lot more oil in a given volume (coal coke is even more porous, thus less dense). I use olive oil in my little lamps but the flame it produces isn't particularly hot- no more so than that of a wax candle. And being a liquid, certainly there's no easy way to pass air through it to the flame to raise the temperature as one does with a bed of coal or charcoal- so it's not exactly suitable for a forge :wink:

Just FYI, I found that various seed oils (sunflower, soybean, sesame, corn, cotton, rapseed and peanut- curiously no listing for olive oil) all have a very similar heating value averaging 39.6MJ/kg (range from 39.2-39.8 ), whereas coal has a rating of 24MJ/kg and coke 29.6 MJ/kg. So the oils do indeed win out by 1.65x.
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#12
I understand that it takes an enormous amount of pressure to cold roll steel, but wouldn't it have been possible for them to roll it hot. Surely that would require far less pressure.
>|P. Dominus Antonius|<
Leg XX VV
Tony Dah m

Oderint dum metuant - Cicero
Si vis pacem, para bellum - Vegetius
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#13
Sure- we're not talking about huge sheets like are made today- just small ones. Absolutely it would have been possible to heat one up and roll it. The article, however suggests the lorica plate that could have been rolled was done so cold. But if it were hammered a bunch first and then rolled to smooth it out and even the thickness, a rolling mill sounds perfectly plausible to me. A huge amount of pressure isn't necessarily required when talking about changing thicknesses by small amounts...
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#14
What about a hand roller of some kind...like the rolling pin you use to flaten dough.
____________________________________________________________
Magnus/Matt
Du Courage Viens La Verité

Legion: TBD
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#15
Quote:What about a hand roller of some kind

ow.
M. Demetrius Abicio
(David Wills)

Saepe veritas est dura.
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