I'm a regular lurker on /r/geology, and we get so many ID requests for what eventually turns out to be slag it turned into a sort of runaway inside joke which isn't even funny anymore (usually the askers believe they found meteorites). Geologically, slag is junk.
example 1, example 2, example 3
But I wonder: from a Historians point of view, what can we learn from slag? When can we tell if it is a significant artifact and when can we tell it isn't? Are there descriptive or analytical approaches which allow to categorize slag and derive usefull information from it? If so what? Where to begin looking at slag as an information source? When some redditor shows me an obvious piece of slag, what should I look for?
Also: whatever you'd like to share/discuss about slag!
Not a specialty of mine by any means, but ancient slag deposits, as archaeological sites, tell us some pretty cool things about the ancient Middle East.
As far as I'm aware it's not so much that some individual piece of slag can tell us much, but the date, volume, location, etc. of slag deposits can tell us a lot about local economies, regional trade, human habitation in the area etc. etc. There may be some chemical analysis of the local slag and copper that's of archaeological value but that's way beyond me.
One example that interests me, mostly because I live in the neighborhood, are the ancient copper slag deposits of Oman. Some of these deposits are 5000 years old. Now, Oman was not actually consuming this copper itself, but rather was exporting it up the Persian Gulf to the Bronze Age Mesopotamian civilizations in pretty enormous quantities.
So for instance there are ancient surface-mining slag-deposits at single locations in Oman with ~40,000 tons of slag. So you have pretty enormous outputs even in locations that are incredibly isolated. And again, we're talking about mining operations that started 5,000 years ago.
But for that much output you also need fuel input. Several times the weight in wood charcoal fuel is necessary to burn a given unit of slag. When you look at Oman, which is a desert country but, like Yemen, actually has an interesting hydrology that allows for quite a lot of vegetation, that wood might have been sourced locally. I don't know if there's more recent scholarship on the question but at least one article I've read suggests that the deforestation of Oman's mountains to fuel slag furnaces may have have resulted in both the collapse of that copper industry by the medieval period as well as the man-made desertification of what had previously been a much lusher environment.
A slag heap is also a pretty good indication that there might well be other related structures in the vicinity. I've visited (purportedly Roman) slag heaps in Wadi Dana, Jordan where, if it were not for the huge pile of slag there would be no indication that there had ever been permanent settlement in the area at all as the current residents are primarily semi-nomadic pastoralists.
Source wise:
See for instance Gerd Weisberger's Patterns of Early Islamic Metallurgy in Oman, or this from the Companion to the Archaeology of the Ancient Near East.
It would be worth bouncing this question off some archaeologists and anthropologists. There are some here, but more over in /r/AskAnthropology: you may want to x-post for more ideas
