I’ve been thinking about doing some writing about slag analysis for a while, and as I’m currently in the lab working on samples this seemed like the best time.
As I have discovered, the subject of slag analysis is like an iceberg – it seems insignificant on the surface, but once you get below the waterline it tends to bulge and grow at a worrying rate. Additionally, slag analysis has the habit of seeming rather mysterious. In the two years I’ve been working on slags, I’ve come to the conclusion that this is down to an almost complete lack of published texts on how to actually do slag analysis. By that I mean: what does the surface texture mean? Why do I want to look at the microstructure? Why are my fayalite crystals cored? What the hell is that weird thing? And what does it all mean anyway?
There are some texts available, but these tend to be named in misleading ways or be down right rare and hard to find. Very few of them focus on actually helping the reader learn to replicate the process with their own material; most are reports on analysis that just happen to be so well done they are inspiring. My particular favourite is actually a PhD thesis from the 1980s by a woman called Fells, working at Birmingham University. Luckily this is available to download, as it represents one of the first thorough technical studies of the microstructures of archaeological slags. In particular, the second volume is full of optical and electron micrographs and accompanying explanations, which really is what you need when you’re staring down the microscope for the first time.
I should mention here that I am not the world’s premier expert on archaeological slags; not their morphology nor their microstructure nor their chemical composition. But I do have a working knowledge, which I endeavour to improve, and I do have access to a great library and great colleagues.
As an aid to my own work, and hopefully to other people interested in the subject, I’m going to write a series of posts looking at different aspects of slag analysis. If I’m very lucky I might even get some feedback from other people studying the subject, which would be very welcome. I’ll try to make it interesting and reasonably accessible, and I can pretty much guarantee that there will be a lot of pictures. Hopefully it’ll be an interesting glimpse into the background to my work, and helpful for anyone trying to decode a specialist report!
Ruth Fillery-Travis 
I have noted twelve bloomery sites in woodlands near to me in Derbyshire, characterised by tapping slags. I would like to try and locate the furnaces and ore roasting sites. What is the best (and cheapest) geophysical prospecting technique to use? I’ve finished my MPhil on woodland archaeology and want to continue with my researches into metal processing locally.
Paul
I’m afraid I haven’t worked with geophysical methods before, so I’m not particularly knowledgable. I’ve seen evidence that geomagnetic methods work well for locating furances and burnt features but I couldn’t say which type is best/most cost efficient. To my knowledge they’re all expensive and your best bet is to borrow/hire equipment off a friendly archaeological unit or university. Really sorry I can’t be more help!