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Hey guys!

Since I was getting some ore from my countryside, I figured I could use the opportunity to do some archaeology as well. My studies allowed me to identify a couple of ancient forges/bloomeries (going as far back as the 15th-16th centuries, some sites are even suspected to come from the Roman era). I was able to get there and find some slag pieces embedded in the ground, right where the studies where hinting :o

Now I'd like to be able to confirm the origin of this slag. Most of it should come from blast furnaces (which became standard in the area around the end of the 15th century). The issue is that I'm not sure how I could differentiate between "real", legitimate, historical slag and the stuff they brought all over the place during the 1870s when they built a bunch of railways along my historical sites.

Do you know any way I could date my slag pieces? I was thinking about breaking some apart to try and find coal pieces inside, but I'm not sure that would work :unsure: 

Thank you guys!

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Well, that is certainly bloomery slag!  Archaeometallurgists go nuts for the stuff, doing all sorts of trace element analysis, polarized microscopy of thin sections, and so on, but what you need is thermoluminescence  dating (TL testing).  This is a dating method which will tell you the last time something was extremely hot.  Unfortunately unless there is a university nearby with a lab manager you can bribe it is not a cheap test.  Somewhere between 250-500 Euros per individual sample is usual.  If there is charcoal in the slag that has been sealed away from the atmosphere you can have radiocarbon dating done, that is cheaper.  Around 50 Euros for regular C14, 150-300 Euros for AMS (accelerator mass spectrometer) dating.  Regular C14 gets you within +/- 50 years for medieval stuff, AMS gets you +/- five years.

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Hi Alan,

Thank you for your insight.

First of all, you're talking about bloomery slag, but my understanding was that it is more likely to be blast furnace slag (which was already standard in my area in the early 1500s). Would there be any to differentiate between the 2 processes? I'm guessing bloomery slags would be much richer in iron than blast furnace slags, but that's about it.

Thank you for your proposed means of dating, that confirms there doesn't appear to be any "cheap", DIY way of doing this :)

I've got to ask, where do you find "basic" C14 dating for 50 €? Every lab  I've searched seems to propose AMS only (your other prices seem on point, though).

Thanks again.

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In general (very general!) bloomery slag from the Catalan process tends to be found in large tabular slabs between 2-10cm thick and is usually dark greenish-black and somewhat foamy-looking. There is often charcoal and unreduced ore embedded.

Blast furnace slags in comparison tend to be more glassy and solid, often showing flow lines, ripples and waves, indicating the tapping of a fully liquid slag into prepared channels. There is usually little to no charcoal or ore entrained with it.  Depending on the chemistry, blast furnace slags range from black to sky blue in color.

I do understand the difficulty in your area, since the transition from bloomery to stuckofen to blast furnace results in a wide array of all spectra of slags.  To make it more annoying, most archaeometallurgists only like very early slags from slag-pit shaft furnaces and bowl furnaces and refuse to look at anything obviously later.  That said, Roman shaft furnace slag resembles blast furnace slag more than bloomery slag. It's just usually in smaller chunks and is always black from the retained iron content.

If you are a member of academia.edu (it's free!) Look up anything by Peter Crew.  He likes the medieval and later stuff too.  And he is very helpful if you seem to know what you're talking about, also unusual in that crowd.

Finally, you are correct, almost nobody does straight uncalibrated C14 dates anymore.  Beta Analytic in the USA will, but they will try hard to steer you to their AMS services.  I know there is a lab in France that can pull a date from iron (!) rather than charcoal.  They recently dated some iron from a cathedral to prove it was original.  Unfortunately it will be Monday before I can get that information, and I am positive they do not work cheap.

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12 hours ago, Alan Longmire said:

I know there is a lab in France that can pull a date from iron (!) rather than charcoal.  They recently dated some iron from a cathedral to prove it was original.  Unfortunately it will be Monday before I can get that information, and I am positive they do not work cheap.

Oh wow, you unknowingly touched one of my other BIG topics of interest here...I've lived since my childhood next to some of the most beautiful French gothic cathedrals. I'm very interested in them, and actually the study of one of them (Beauvais) is what brought me to ore smelting :)

Maybe that's the one you're talking about, but there has been some discussion for years whether wrought iron found inside some cathedrals was from the very type I'm working on right now. If you do have any information about a lab that's working on this topic, I am indeed incredibly interested.

Thank you for mentioning Peter Crew, did not know about the guy but I'll check.

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Its also worth remembering that in many places blast furnaces were run from charcoal for a long time and the use of coal is generally a much later event and often limited to areas with good low sulphur coal seems.

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