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All That Glitters, Experiment 5

Fittingly in some ways, given the distressing news of the last post, this post takes me back to Birmingham (which continues to happen, with a trip there on Wednesday coming that I will delight in telling you about before long if all goes to plan…). In fact, this is the last of the posts promised in my second Chronicle round-up, which means that we are now progressed in the story of my academic life to December 2015… It doesn’t look a lot like blogging progress, but let’s ignore that and instead tell the next part of the story of my project to zap Byzantine gold coins with X-rays, All That Glitters.

Bruker S8 TIGER XRF analyser open for business

The maw of the S8 TIGER XRF analysis machine in the Department of Chemistry, University of Birmingham, already much featured in these posts

It’s getting a little silly now to re-summarise the project every time I do one of these posts, however far apart they may be, so I’ll invite you to look here for the premise and just say where, by December 2015, the project had got up to. In brief, we had started from a belief that we might be able to find out about sources of metal for the Byzantine coinage and how those changed and maybe why by analysing them using a technique known as X-Ray Fluorescence (XRF). We got money to investigate this possibility in April 2015, and either before that or thereafter moved through the following developmental steps:

  1. finding out that the lightweight, energy-dispersive kit that we had hoped to use just wasn’t going to get the information we needed;
  2. finding out that the big, stationary, wavelength-dispersive kit we had to use instead (by kind courtesy of the Department of Chemistry, University of Birmingham) would get us the best results only on its longest cycle, cutting the number of things we could test in the time we could pay for down considerably;
  3. finding out that the results we were getting apparently included quite a lot of invisible surface deposits that seemed most likely to be leftover soil;
  4. discovering that, against all expectations, cleaning the coins in acetone actually made this problem worse, if anything;
  5. deciding, along the way, that we could not, as we had hoped, test different areas of coins for comparison of homogeneity either, because the results were just too darn variable to interpret;
  6. establishing that despite all these limitations, we could still distinguish between mint practices sometimes, but that only in the most difficult of cases was this telling us anything a competent numismatist couldn’t have seen by thmselves;
  7. and, although this was my colleague Dr Rebecca Darley, not myself, presenting these initial findings at the International Numismatic Congress in Taormina and at the Joint British Museum/Institute of Archaeology Seminar at University College London.1
  8. At the former of these presentations we got some pushback from the numismatists whose work we were implicitly questioning, which was understandable, but in the latter we got lots of pushback from one or two archaeometallurgists who felt that we were not people properly trained to do such work and that in fact it was pointless, which I saw as one of those ivory-tower problems; people are out there doing such work badly anyway, so would you rather just let them publish it and be accepted or shall we aim to do at least a bit better?2 Admittedly, we were having trouble doing much better, but that was what we now set about solving…

On 17th December 2015, therefore, three of us brought our test set of coins back to the Department of Chemistry, but this time with a difference. We’d already tried cleaning the coins in acetone, as said, so we had decided that we needed to try harder. But how hard should you try to clean a relatively soft precious-metal object of considerable value? Thankfully, this was a question that the team working on the Staffordshire Hoard had already faced, and since I’d been able to talk with one of them earlier in the year, we had a kind of answer, which was, berberis (or barberry) thorns: tough enough to shift surface dirt, soft enough not to scratch the metal!3 So before the test, Maria Vrij, by now in post succeeding me as Interim Curator of Coins at the Barber following my move to Leeds, had taken the coins and more acetone down to the Barber’s most suitable room for the purpose and, with the windows wide open, had laboriously worked over their surfaces with thorns under a magnifying glass.4 I can only say that this made me very glad to have moved jobs before this could have become my task, and I remain very grateful to Maria for doing it, but of course the real question was, what difference did it make? And the answer was, sadly, ‘a bit’: the levels of presumably-surface material that shouldn’t really be in the coins (calcium, silicon, potassium, aluminium) dropped, but were not gone.

A gold solidus of Emperor Heraclius struck at Constantinople in 613-616, Barber Institute of Fine Arts B2762, in a WD-XRF sample cup

A gold solidus of Emperor Heraclius struck at Constantinople in 613-616, Barber Institute of Fine Arts B2762, in its WD-XRF sample cup for testing

This was, in many ways, not the answer we wanted, as with so many of the findings thus far. We would much rather not have had to use the big, fixed machine to which the coins had to be brought, rather than one of the portable ones we could have taken to other collections; we would rather have been able to use a shorter test cycle and thus test more things in the time we had; we’d rather not have had to clean the coins at all; but if we had to clean the coins, we’d rather it had been possible just with a wash and a rub in acetone, not with hours of picking at them with thorns with your face close over a bath of solvent. If we had (and by we, I really mean Maria, sorry Maria), to do all that, however, we’d at least have liked it to produce good results. What it actually produced, however, was only measurably less bad results, which was not the exciting scientific conclusion for which we might have hoped. But it might be a bit more like actual science, and sadly, it’s a lot more like real life; messy, never quite sorted out, but still interesting…


1. The former of these papers is now published, in fact, as Rebecca Darley, “All that glitters…: the Byzantine gold solidus, c. 300-1092″, in Maria Caccamo Caltabiano (ed.), XV Internationa Numismatic Congress, Taormina 2015: Proceedings (Rome 2017), II, pp. 982-985. A cite for the latter would be Rebecca Darley, “What does the science mean? Interpreting metallurgic analysis of Byzantine gold coinage”, unpublished paper presented at the British Museum/Institute of Archaeology Joint Seminar, University College London, 15th December 2015.

2. It seems mean to point fingers, but once it’s being cited it is probably fair game and, on the basis of our experiments, I might raise questions about Rasiel Suarez, “A Metals Analysis of Silver Roman Imperial Coins using X-Ray Fluorescence Spectroscopy”, online here, whose precision just seems impossible with the equipment he used despite his checks (which were not carried out against a standard), and one would like at least to be able to ask more questions about the methods and reproducibility of the tests in Monica Baldassarri, Gildo de Holanda Cavalcanti, Marco Ferretti, Astrik Gorghinian, Emanuela Grifoni, Stefano Legnaioli, Giulia Lorenzetti, Stefano Pagnotta, Luciano Marras, Eleonora Violano, Marco Lezzerini and Vincenzo Palleschi, “X-Ray Fluorescence Analysis of XII–XIV Century Italian Gold Coins” in Journal of Archaeology (2014), pp. 1–6, online here. Note that we are not the only researchers wondering about things like this, by now: see also V. Orfanou and Th. Rehren, “A (not so) dangerous method: pXRF vs. EPMA-WDS analyses of copper-based artefacts” in Archaeological and Anthropological Sciences Vol. 7 (Basel 2015), pp. 387–397, DOI: 10.1007/s12520-014-0198-z, and E. S. Blakelock, “Never Judge A Gold Object by its Surface Analysis: A Study of Surface Phenomena in a Selection of Gold Objects from the Staffordshire Hoard” in Archaeometry Vol. 58 (Chichester 2016), pp. 912–929, DOI: 10.1111/arcm.12209.

3. See ibid.!

4. Of course, she is no longer Interim, but now actually properly Curator of Coins, and much better at it than ever I was, despite the acetone fumes!

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Crusading and a Non-Deterministic Climate

The marking ebbs, and the ability to blog reappears… And for once it is clear what I should blog about, because I said I would pass over Conor Kostick‘s long-ago paper to the Digital Humanities Seminar in the Leeds Humanities Research Institute (which, as every sub-university-level academic organisation must every few years, has since changed its name), and then Dr Kostick himself cropped up in comments encouraging me not to, and so it seems rude to refuse. I admit that part of my initial reservation was that I might have to be rude, but now that I review my notes, even though the paper was called, “Digital Linguistics and Climate Change: a Revolution in the Digitisation of Sources since 2000”, which you can imagine annoying me in several ways I’m sure, I find less to be annoyed about than I remembered, but also less that one might call, well, conclusive.

Saul killing King Nahash and destroying the Ammonites, in the so-called Crusader Bible (c. 1250), New York City, NY, Morgan Library, MS M.638, fol. 23v

Saul killing King Nahash and destroying the Ammonites, in the so-called Crusader Bible (c. 1250), New York City, NY, Morgan Library, MS M.638, fol. 23v, image copyright not stated

Dr Kostick’s research at this time had arrived at the central theme of his paper from a circuitous direction. Starting with the study of the Crusades, he’d got into digital humanities as a lexicographical way of working out what medieval authors most probably meant by the words they used, which were of course changing as they used them. His example here, an interesting one, was that Archbishop William of Tyre, Chancellor of the Kingdom of Jerusalem already, may have been the first author to use the Latin word classis, classically meaning ‘fleet’, to mean ‘class’, as in first- and second-class, which are ways he divided up the nobility of Jerusalem in terms of tax liability. That wouldn’t have been clear without being able to find all the places he uses and all the places other people do and thus being sure that his is the usage that seems to begin it. This kind of technology lets us get further than the grand old lexicographers of old such as Charles Du Fresne Du Cange; as Dr Kostick put it, “we are standing on the shoulders of giants, with big binoculars”.

Charles Du Fresne Du Cange, from David d’Angers and Alfred Gudeman, Imagines philologorum (Berlin 1911), p. 19

Du Cange himself, from David d’Angers and Alfred Gudeman, Imagines philologorum (Berlin 1911), p. 19, public domain via Wikimedia Commons

From here, however, he had gone via an investigation of crusade preaching and had wound up at medieval climate data, not an obvious transition you might think, but several paths lead there. One is the kind of work that has been, let’s say examined, here before, attempting to correlate major political and social upheavals with climate events; another is the fact that at least one historian of the First Crusade, Ekkehard of Aurach, actually made the association for us, saying that the massive participation in that Crusade was at least partly down to a bad harvest, famine and ‘plague’ (perhaps ergotism, suggested Dr Kostick) in France that meant people with no other hope were willing to sign up with someone with a poorly-realised plan and take their ill-informed chances.1 The problem with many such analyses looking for other correlations, apart from the basic logical one of the difference between correlation and causation, has been poor focus of data, using, for example, tree growth in Greenland as a proxy for harvests in continental Europe, and this Dr Kostick avoided by taking as wide a range of sample evidence as possible. He started with chronicles, especially, using the same text-mining techniques as already mentioned, counting entries mentioning famine, plague and strange weather; added tree-ring data from a range of different areas (assembled by Francis Ludlow); and used ice-core data from Iceland and Denmark for finer dating. It’s a pretty good sample, as these things go, and this obviated many of the objections to such work I’d gone in with. So having done that, what do we then know? Well, the texts make it clear that both in 1095 and 1146, i. e. just before the First and Second Crusades, there were outbreaks of disease, which the tree-ring data suggests often coincided roughly with years of poor tree-growth, and the ice-core data sometimes allowed one to associate these and other such peaks with volcanic eruptions.

(I went looking for a climate data graph to put in here but the amount of short-sighted nature-blaming one quickly finds just made me angry so you’ll have to manage without an illustration between these paragraphs.2)

So case proven? Well, sometimes. It’s certainly possible, especially in the light of Ekkehard, to imagine how such a causal chain could fit together: a ‘year of no sun‘, poor crop yields, famine, destitution, desperate mobility, a convenient casus belli or particularly effective preacher, and suddenly what was meant to be a few thousand carefully-picked troops heading East, probably on the expectation of campaigning on an imperial salary for a few months, has become a horribly underplanned mass movement that winds up changing the world.3 The problem is that the chain doesn’t always work the same way. That works very well for the First Crusade, but in the Second Crusade, the popular participation was nothing like as large, though it was certainly large enough for Odo of Deuil to lament, I’ll admit; still, it was provoked by the fall of Crusader Edessa in 1144, and preparations were well underway by 1146 so I’d have thought that popular uptake is all that the bad year could have affected. Meanwhile, there was another significant peak between these two Crusades (not at 1101, at 1130 or so) which correlates with no such action, and there was no such peak before the Third or Fourth Crusades. Hey, maybe that’s why the Fourth Crusade couldn’t raise enough men, right? But the Third still presents problems.

A 15th-century image of the conquest of Constantinople by the Fourth Crusade, from  David Aubert, Livre traittant en brief des empereurs, II, fo. 205r

An unexpected result of a bad harvest? Probably not, eh? A 15th-century image of the conquest of Constantinople by the Fourth Crusade, from David Aubert, Livre traittant en brief des empereurs, II, fo. 205r, says Wikimedia Commons where this image is public-domain

Obviously, this paper was never meant to present a thesis as simple and obviously falsifiable as ‘volcanic eruptions caused the Crusades’, but without that, what do we learn from it? Our chroniclers already told us that plague and famine powered recruitment for some of the Crusades, and we didn’t need text-mining to see that. We might, now, understand better where that plague and famine had come from in these cases, but as with my earlier critique of Michael McCormick’s similar deductions about volcanoes, the problem lies in the volcanic eruptions that did not cause crusades, the famines and plagues that were not caused or strengthened by climate events, the crusades that did not correlate with bad weather or famines, and so on.4 No general rules could be extracted from this sort of causation, and neither was Dr Kostick out to present some, but without some such finding, it seemed like a very laborious way to conclude that a couple of our sources were maybe more right than we sometimes reckon. There seemed no question that Dr Kostick and his team had been more careful with data and correlations and even with causation than previous studies, but naturally enough perhaps, that had also limited what they could conclude.

That was my feeling as Dr Kostick wound up, anyway, but questions revealed other doubts and issues among the audience, many of which I thought he actually had good answers to. One of my colleagues argued that climate event references in chronicles are often wrong, to which Dr Kostick wisely observed that this was a good reason to correlate them with scientific data. Other questions focused more justly on causation: Graham Loud has in the past argued, apparently, that a famine which preceded the Third Crusade actually limited response from Germany, and here again Dr Kostick argued that while local responses to stimuli would obviously have varied, the bigger correlations still need explanation when they occur. True enough, but that seems to have been very rare… Well, I certainly don’t have better answers, and if Dr Kostick had been unwise enough to try and push his data further than it would go I imagine I’d have had bigger issues with that, but my feeling remains on this revisiting that his admirable caution robbed the paper of its potential power. The success of McCormick et al. suggest that, sadly, the route to publication of such work is not to care about such things but to push the deductive boat out well beyond sensible recovery, and maybe that’s why this one didn’t (yet?) achieve wider dissemination; it just wasn’t crazy enough!


1. F.-J. Schmale and I. Schmale-Ott (edd.), Frutolfi et Ekkehardi Chronica necnon Anonymi Chronica Imperatorum: Frutolfs und Ekkehards Chroniken und die Anonyme Kaiserchronik, Ausgewählte Quellen zur deutschen Geschichte des Mittelalters 15 (Darmstadt 1972), pp. 19-38 (commentary) & 123-309 (text), cap. 13/40, pp. 124-127, the relevant section transl. J. H. Robinson in Readings in European History Vol. I (Boston 1904), pp. 316-318, online ed. P. Halsall as “Medieval Sourcebook: Ekkehard of Aurach: On the Opening of the First Crusade”, online here.

2. I should clarify that the thing I think is stupidest in these arguments is neither that there is dispute over climate change at all, which I find explicable if dangerous, nor that there is argument over its causation, which is predictable really, but the conclusion that some people who believe climate change now is not anthropogenic reach that therefore we need do nothing about it because it’s natural. I imagine these people largely do not live in the areas most affected.

3. This interpretation of events largely rests on my old piece linked off this very blog, but is similar to that put forward in Peter Frankopan, The First Crusade: the call from the East (London 2012).

4. My target here is of course Michael McCormick, Paul Edward Dutton and P. A. Mayewski, “Volcanoes and the Climate Forcing of Carolingian Europe, A.D. 750–950”, Speculum, Vol. 84 (Cambrudge MA 2007), pp. 869–895, online here.

All That Glitters, Phase 4

The times continue strange in UK higher education, as you may have seen. Many of us are on strike for what is now the third week, more of us than ever now, and the employers’ representatives appear to be refusing to negotiate in person and then changing their mind by Twitter overnight. I don’t know what may happen in the next 48 hours and of course in case classes happen, they all have got to be got ready on the few days when we’re not on strike, in case something is resolved that means we go back to work. But, what this does mean is that my conscience is pretty clear about blogging. Having taken my first steps down a new road in the previous post, it thus behoves me to look around myself and say, ‘What was I doing in July to September 2015 that I haven’t already told you about?’, and the answer to that is not limited to but certainly includes, ‘zapping gold coins with X-rays some more’. So this is about our fourth set of tests.

Jonathan Jarrett and a gold solidus with XRF machinery in the Department of Chemistry, University of Birmingham

Posed, obviously; I may look intrepid, but you have no idea how tightly I was holding that coin. It rolling under the machine would have spoiled several people’s day quite badly…

If you remember, where we were with this is that having got money to evaluate techniques by which we might be able to use X-ray fluorescence spectroscopy to measure the metal content of Byantine coins, with an especial eye on trace elements that might betray metal sources, we had fairly quickly established that the kind of portable machinery which we could bring to the coins in their museum wouldn’t tell us what we needed to know. So the working set-up for these experiments was now that, after having checked our insurance quite carefully, as soon as I could get into the Barber’s coin room of a morning I would remove from it about 100 g of high-purity gold in the form of 20-odd Byzantine and other coins, then University security would turn up (in theory) and transport me to the School of Chemistry (in theory). We would then do as much zapping as could be done, with at least two people present where the coins were at all times, before Security turned up again (in theory) in time to get me and the coins back into the Barber before it closed. And this time we did this for four days running. I won’t tell you how many ways this process could go wrong, but I haven’t flagged them all. But Chemistry were lovely and very generous both with expertise and with biscuits, and though we never had quite the same team there two days together it was all quite a good group exercise anyway. So, what were we doing this time and how did it go? The answer is a long one, so I’ll put it behind a cut, but do read on! Continue reading

All That Glitters, Experiment 3

A problem with finally picking up this blog a bit is that some of the old stories in it have been sitting idle for really quite some time. Does anyone remember, for example, that while I was working at the Barber Institute we got a small amount of money to zap gold coins with x-rays? If you do, you may remember that I’d already reported on the first two experiments we did in that project when everything here ground to a halt in 2016. Well, now I resume, with a brief account of the third experiment we did, and before long who knows, we may be through the rest!

Bruker S8 TIGER XRF analyser open for business

The S8TIGER WD-XRF spectrometer in the Department of Chemistry, University of Birmingham, with five sample cups waiting and one under analysis

A brief recap may be in order first of all, though. The very short version of the project’s purpose was: we had all seen an increasing amount of work using X-ray fluorescence spectrometry to analyse the fineness of precious-metal coins and sometimes even assign origins to its metal based on the trace elements therein. We had our doubts about this, but the manufacturers of some of the best machinery involved wanted to quell our doubts about this and offered us quite a lot of help with it, so we came up with a plan and, somewhat to our surprise, got both permission from the Henry Barber Trust to muck around with their coins and funding from the Royal Numismatic Society to do it, and so set about it. We began this in December 2014, with two experiments. The first was designed to test the viability of hand-held, portable, energy-dispersive machinery that could be brought to the coins; the second did comparator analyses using a fixed-location wavelength-dispersive spectrometer to which we had to bring the coins. This showed us that to detect anything at all of trace elements we would need the big machine, but also that it was picking up a whole load of stuff that seemed very likely to be extraneous material on the surface of the coins, probably from the soil in which they had long ago been found, rather than the stuff of which they were actually made. And that is about where we come in!

Gold solidus of Emperor Constantine VI and Empress Eirini struck at Constantinople 785-797, Barber Institute of Fine Arts B4599

The coin whose results (and details) are given in the first table below, set up for the test in which it did so

So, the third experiment was very simple. Using the same set of coins as we had previously run, I got hold of some conservation-quality acetone and a toothbrush, took them and the coins down to a workroom in the depths of the Barber and gave them all a careful but thorough scrubbing and let them dry, all except one that we left uncleaned as a check. Then I packed them up again and we bore them off to the Department of Chemistry on 22nd July 2015. There we ran them again, on the shorter of the big machine’s two cycles, and this gave us some results both before and after cleaning.

Unfortunately, if anything, the post-cleaning results showed more extraneous grot. That ‘if anything’ will tell you, though, that consistency was hard to observe. The variation wasn’t vast amounts, you understand, between half and one-and-a-half per cent, but cumulatively certainly enough to push our figures for the actual gold content up or down by two or three per cent, which would for some people be enough on which to found a theory about debasement… Here are the top ten elemental results from just one side of one coin by way of example:

Coin 170 (obverse)1 Percentage observed first time Percentage observed second time
Gold 86.51% 84.49%
Silicon 3.44% 4.63%
Silver 1.61% 1.43%
Aluminium 1.27% 1.19%
Potassium 0.80% 0.63%
Sodium 0.74%
Copper 0.44% 0.34%
Calcium 0.32% 1.96%
Sulphur 0.28% 0.48%
Iron 0.27% 0.50%
Total percentage of coin observed 96.38% 96.70%

Down by two per cent gold, and that mostly gone to silicon and calcium, even though some other small elements had dropped in the readings as well. Also, what this arrangement doesn’t show, the second time small but possible readings showed up for chlorine, magnesium and, way down the scale, platinum, all absent the first time through. Surely cleaning with acetone couldn’t have added calcium to the coin? But each coin we ran had its own little tale of additional mess to tell, even (and this should have told us something) the uncleaned check. Here are its top-ten figures for the obverse:

Coin 21 (obverse)2 Percentage observed first time Percentage observed second time
Gold 82.57% 87.43%
Silicon 1.82% 1.61%
Aluminium 1.01% 0.81%
Silver 0.74% 1.10%
Sodium 0.65%
Potassium 0.47%
Chlorine 0.45%
Calcium 0.44% 1.78%
Iron 0.31% 0.31%
Copper 0.24% 0.26%
Total percentage of coin observed 89.12% 93.80%

Some things are beguilingly similar, yes—iron and copper levels stay about the same—but others are not. The first test picked up sodium, potassium and chlorine but none of those turned up second time even though we’d actually got better readings with more of the sample observed (possibly because we gave it a flatter bit to look at). Were we just looking at a different bit? If so, that bit apparently had less silicon in it, but a whole whack more calcium in it. What can you do with these sorts of data?

Gold solidus of Emperor Anastasius I struck at Constantinople 491-518, Barber Institute of Fine Arts B0006, in an WD-XRF sample cup

The uncleaned check likewise set up for the results above, though I have to say it’s not like it looks dirty

So this was somewhat daunting, especially as we had four solid days of testing booked in for the following week and now somewhat less certainty that it would produce anything. At the time, my best guess was that the acetone had removed only handling patina, thus exposing the actual surface of the coin and everything that had adhered to or reacted into it while it was in the ground. Actually, looking back, I think we were already seeing here the conclusion that the final experiment would necessarily lead us to. But that would be getting ahead of the story, and even though this story is so very far behind, I have hopes of telling it as I wanted to anyway. So, till next post but, er, two, if I have my plans right (and no-one else dies—did you see Mark E. Smith has left us for the bar of the great and final WMC since the last post?), I shall leave the question hanging…


1. We used randomly-allocated running numbers throughout these experiments, so that we couldn’t try and guess what the results should be according to where the coins fitted in Byzantine history (or the previous curves laid down by work like Cécile Morrisson, Jean-Nöel Barrandon and Jean Poirier, “La monnaie d’or byzantine à Constantinople : purification et modes d’altérations (491-1354)” in Morrisson, Claude Brenot, Barrandon, Poirier and Robert Halleux (edd.), L’or monnayé I : purification et altérations de Rome à Byzance, Cahiers Ernest Babelon 2 (Paris: C. N. R. S. 1985), pp. 113–187. This one was actually Birmingham, Barber Institute of Fine Arts B4599, a solidus of Emperor Constantine VI and Empress Eirini struck at Constantinople between 785 and 797, online here. I’m actually almost loath to identify the coins here, though, lest it be thought I’m actually publishing figures for their metal content. As is probably clear, though, that’s something I’m sure we weren’t reliably getting.

2. And this one was Barber Institute of Fine Arts B0006, a solidus of Emperor Anastasius I struck at Constantinople between 491 and 518, online here, with the same reservations as in the previous note.

All That Glitters, Experiment 2

Somehow my posts about me and my work—and that may not be what you’re here for but, you know, I like it—have got behind my seminar reports in such a way that they’re into February 2015 and I’m still in December 2014. Let me resolve some of that disparity by giving you a short report on the second day of experiments in the collaborative project I’m in for analysing Byzantine gold coinage by X-ray fluorescence, which was 14th December. (If you need background I announced this project ages ago here and dealt with some of our starting questions and the first day’s experiment here.)

Cover of J. O. Jeppson, The Second Experiment

Our results have so far not been this dramatic, but then, I’m guessing that our first experiment wasn’t quite as adventurous as this must have been

To recap, we had established that if our experiments were to tell us anything much about elements other than gold, silver, copper and maybe one or two other pre-determined elements, we were going to need not the energy-dispersive machinery we’d been using on the first day but the bigger, more expensive and, most importantly, immobile wavelength-dispersive machinery in the Department of Chemistry in the University of Birmingham, a machine called the S8 TIGER. I am only just able to describe the difference between these two analytic methods: in so far as I can, it’s to do with what is being used to pick up the energy given off by the things you’re bombarding with x-rays. The WD machinery includes crystal collimators that are sensitive to certain wavelenths of that energy, which therefore get picked up better, where the ED machines, which measure only in terms of intensity of signal, simply wouldn’t see such things among the massive gold return, as we had surmised. The WD machine also scans its samples in a vacuum, which eliminates interference from the air.

Bruker S8 TIGER XRF analyser open for business

The mouth of the TIGER yawning wide, with five sample cups waiting and one under analysis

On the other hand there are also problems with the WD machinery that don’t exist with the ED kit. For us the first of those was simply access; it’s nothing to do with the actual machinery except in so far as it’s immovable, but because we had to take the coins to the kit rather than vice versa, that meant arranging transport and insurance even on campus, and the transport repeatedly went wrong, which cut into our experimental time a lot. But, also, the ED kit works with narrow beams focussed on points; the WD machine scans its samples in masks such as the one below, of which the two sizes relevant to us were 5 mm and 8 mm, and those were therefore the only area sizes that we could analyse. Importantly, this also precluded examining coins at their edges or over piercings, because the sample has to fill the exposed area completely. This also highlights a problem with both ED and WD methods: non-homogeneity. If for some reason your coin had an odd tiny lump of platinum on its surface, say, the ED machinery would either miss it (in which case you’d never know) or find it and report a massive platinum signal (which would be misleading for the coin’s overall composition). The WD machinery, however, would factor it into the average, so that you wouldn’t necessarily realise that it was a coherent inclusion rather than a component of the main alloy. So there was plenty to worry about even if the machine worked perfectly.

Emperor Heraclius just visible on one of his solidi of Constantinople loaded behind an 8 mm mask for analysis in the Bruker S8 TIGER

Emperor Heraclius just visible on one of his solidi of Constantinople loaded behind an 8 mm mask for analysis

Anyway, we had our goals clear for this test. The first was to get our hands on the machinery and find out what the operational considerations in any further planning were, the results of which you sort of see in the musings above. Here I have to acknowledge the tremendous help and general goodwill of Dr Jackie Deans, official keeper of the TIGER, and Dr Adrian Wright, who had first let us involve the Department of Chemistry in the project and had helpful things to say whenever he dropped in. Our second priority was to run the same ten coins around which we’d built our first experiment on the S8 TIGER and see how the results differed from those on the ED kit. And as it turned out, our third one was to determine how we wanted to use the S8 TIGER, because as Jackie explained to us, it could analyse at three levels, a 2-minute cycle that would probably get us no more data than the ED machinery had, an 8-minute one which should do the job, and an 18-minute one which was the very most data it could gather. Adding 10 minutes to each analysis was obviously going to limit the number of coins we could actually analyse in any given timeframe, so we really rather needed to know whether or not it was worthwhile.

Gold solidus of Empress Eirini at Constantinople set up for analysis in a Bruker S8 TIGER XRF analyser

The rather different visage in gold of the Empress Eirini, likewise cruelly cut down to 8 mm of glaring royalty

And so what did we find? Well, this machine certainly had more to tell us. We were now getting returns in terms of many elements, at concentrations of down to parts per thousand or even less. This ineluctably meant a decrease in gold concentration reported, because there was now simply more data to fit into the percentages, but the overall picture of lots of gold, not much silver and less copper was still very apparent in the reported figures. What we hadn’t expected, and had now to deal with, was that copper wasn’t usually the third most detected element, and sometimes silver not the second: instead, we were seeing lots of calcium, silicon and sometimes aluminium beating them out. It seemed a priori unlikely that these were original metallic components of the coins in these quantities. That in turn implied that these elements had got into, or much more likely onto, the coins since striking, be that from use, preservation or anything else that might have happened to them. But, whatever they were, they also seemed to be more consistently detected on the long cycle than the medium-length one, meaning that we were going to need to use the long analysis to have any chance of consistent findings. So now we had two difficult questions to answer in setting up Experiment 3: firstly, what could we get done with less than half the scans that we might have hoped to do in any given day of experiments, but secondly, when we did, could we determine whether these results were merely contamination or do anything about that if they were? And these were things which we attempted to address in the New Year, so I’ll stop here for now.

All That Glitters, Experiment 1

Almost the last academic thing I did last year before breaking for Christmas was the first two sessions of a project that is now nearly finished, All That Glitters, announced here so long ago. It was so long ago that it might be worth reintroducing. Basically, by great happenstance one of my predecessors in taking care of the coin collection at the Barber Institute had run into two people at a conference who were presenting about the ability of the X-ray fluorescence (XRF) equipment their company, Bruker Industries Ltd., produced to do metal analyses. That predecessor, Rebecca Darley, also knew Robert Bracey at the British Museum, who had done work with XRF on the coinage of the Kushan Empire, and now I was in charge of the Barber’s coins. None of us are archæometallurgists and our knowledge of archæology and numismatics didn’t necessarily combine with the metals analysis expertise upon which we could call so as to somehow make a composite archæometallurgist out of us all, but Robert could borrow the British Museum’s handheld XRF scanner, Bruker had a new machine they wanted to test against real problems, the Barber is on the same campus as several much larger and more expensive machines also supplied by Bruker some of whose host departments proved happy to let us use them and to tell us about them; a project seemed obviously to exist in potentio and our task was to work out how to make it tell us something useful.

Bruker Industries Tracer IV handheld XRF analysis system

I’m not sure if this is the exact machine we were using but its resemblance to a phaser seems impressively reminiscent

It’s too early to say whether we achieved that, pending actual publication of our results and conclusions which we are even now working on writing up, but right from the beginning it was clear to us that before we could have any historical conclusions we would have to have methodological ones. This is because there are so many potential problems with XRF analysis, problems which not all publications using it consider, and when they do, consider most often for silver alloys rather than the high-purity gold we would be testing, that the first priority had to be not to find things out, but rather to find out what we could find out.1 Accordingly, our pilot experiments were designed to evaluate the machinery more than the coinage, and we started on the 3rd December 2014 when Robert brought the British Museum’s handheld scanner up from the British Museum, along with its calibration standard, and Mike Dobby and Colin Slater from Bruker brought in their new M1ORA energy-dispersive scanner and we put some coins through their x-rays.

A gold solidus of Emperor Anastasius I struck at Constantinople (in the Eta <i>officina</i>) between 492 and 507, Barber Institute of Fine Arts B0005

The first coin to go under, a gold solidus of Emperor Anastasius I struck at Constantinople (in the Eta officina) between 492 and 507, Barber Institute of Fine Arts B0005

We had chosen a test set of ten coins running from Anastasius I (491-518) to Constantine VI (785-797), with two coins for each ruler from the same mint and if possible, the same workshop of the mint (if that’s what officinae were), hoping that whatever results we might obtain would thus be internally secure against outlier coins from a bad day at the mint or similar.2 All of those got zapped on both sides with both handheld and the microwave-like M1ORA. Both of these use a spot beam, but with the M1ORA it’s possible to target it precisely, so we aimed for flat surfaces wherever possible.

Bruker Industries M1ORA XRF analyser at work in the Coin Study Room of the Barber Institute of Fine Arts, University of Birmingham

The M1ORA at work in the Barber’s Coin Study Room, with team members in eager attendance

The initial results of this made the handheld device look like much the poorer sibling, as its readings were extremely variable. Robert worked out, however, that this was related to how much of its expected sample it had been able to observe—this in turn probably down to surface relief but already we were into unknowns—and when the figures were all normalised to a notional 100% of sample they came out much more like what the M1ORA was seeing. The M1ORA was able to dump its readings straight into a laptop equipped with suitable software, and did this levelling-up in that software, so made things immediately clearer for us by automating that step, solely an issue of configuration but we still needed to be aware of it. I keep stressing variables and difficulties because I don’t want to imply that we were getting actual true results, but that said, once they were both talking to us in the same framework the message of the machines was pretty consistent: all these coins were being analysed as very high-purity gold, 97% or more, which is astonishingly high for any pre-modern metallurgy. However, other than silver and copper, which occurred in about the proportions one would expect (i. e. not very much and even less), the only other element that was consistently detectable was iron. That was in part a factor of what we had asked Mike and Colin to make the machinery look for but if you have to do that at all, there is obviously a restriction inherent in your question-setting…

A gold dinar of Sindh imitating a Persian dinar of Shah Shapur II (309-379), struck at an unknown mint and date, Barber Institute of Fine Arts S0073

So then for something rather different, a gold dinar of Sindh imitating a Persian dinar of Shah Shapur II (309-379), struck at an unknown mint and date, Barber Institute of Fine Arts S0073

The very high fineness was sort of what we might have expected, anyway, as it is roughly what earlier analyses of Byzantine gold coins by a number of methods have suggested.3 It still made me uncomfortable for its lack of variety, however, and so since we had run-time left in the day I started hauling other things out of the cabinets. These included two Persian gold dinars, of Shahs Shapur II (309-379) and Varhran IV (388-399), and the above piece which is pretending to be something like the former, as well as an Arab-Byzantine solidus from Carthage and some more Byzantine pieces. Mainly I just wanted to be sure that the machinery actually would report lower gold finenesses, and so it duly did, with the Persian pieces both lower (but not by the same amount) and the Sindh piece even less fine (which, to be honest, was already apparent in its colour, but that was why I’d chosen it). The Byzantine stuff, and the coins imitating that, remained high in the machinery’s estimation.

A gold solidus of the second reign of Emperor Justinian II, struck at Constantinople between 705 and 711, Barber Institute of Fine Arts B4464

Another part of the starting sample, a gold solidus of the second reign of Emperor Justinian II, struck at Constantinople between 705 and 711, Barber Institute of Fine Arts B4464

This bit was fairly unsystematic sampling, but it did give us some reason to believe that the machinery was observing something consistent with our expectations, and which therefore fitted into existing understandings of the early Byzantine gold coinage. That is circular, though, obviously! This and the likely effect on the readings of differences between the surface of the coins and their cores, because of both manufacturing factors and subsequent environmental exposure, meant that we weren’t willing (and still aren’t) to say that these figures are actually how fine those coins were. We also weren’t seeing a range of trace elements which we had expected on the basis of older work, and which might have suggested things about changes in metal supply and treatment that would potentially be historical evidence.4 So, while these machines might serve other people’s purposes, we ourselves were going to need some bigger kit. And that would be Experiment 2, about which I shall write in a couple of posts’ time. In the meantime, however, here is some shiny metallic blogging for the Christmas season and I wish you all a happy holiday!


1. Part of our problem was that so much of the literature about these problems was old enough to relate, potentially, only to a much more primitive incarnation of the technique. Nonetheless, Michael F. Hendy & J. A. Charles, “The Production Techniques, Silver Content and Circulation History of the Twelfth-Century Byzantine Silver Trachy” in Archaeometry Vol. 12 (Oxford 1970), pp. 13-21, William A. Oddy, “The Analysis of Gold Coins—A Comparison of Results Obtained by Non-Destructive Methods”, ibid. Vol. 14 (1972), pp. 109-117 and J. Tate, “Some Problems in Analysing Museum Material by Nondestructive Surface Sensitive Techniques” in Nuclear Instruments and Methods in Physics Research Part B Vol. 14 (Amsterdam 1986), pp. 20-23, all suggest that differences should be observable between surfaces and cores of coins and between methods that measure only the surface and those that measure total composition, and L. Beck, S. Bosonnet, S. Réveillon, D. Eliot & F. Pilon, “Silver surface enrichment of silver–copper alloys: a limitation for the analysis of ancient silver coins by surface techniques”, ibid. Part B Vol. 226 (2004), pp. 153-162, DOI: 10.1016/j.nimb.2004.06.044 and Vasiliki Kantarelou, Francisco José Ager, Despoina Eugenidou, Francisca Chaves, Alexandros Andreou, Elena Kontou, Niki Katsikosta, Miguel Angel Respaldiza, Patrizia Serafin, Dimosthenis Sokaras, Charalambos Zarkadas, Kyriaki Polikreti & Andreas Germanos Karydas, “X-ray Fluorescence analytical criteria to assess the fineness of ancient silver coins: application on Ptolemaic coinage” in Spectrochimica Acta Part B Vol. 66 (Amsterdam 2011), pp. 681-690, DOI: 10.1016/j.sab.2011.08.001, give some explanations of why that should be so. (I have to thank Dr Eleanor Blakelock for some of these and several other useful references.) All of these except Oddy and Tate were working with silver alloyed with base metal, however, and so another of the problems we have is in knowing how far the same applies to gold and if it does, whether if alloyed with base metals only or also with noble metals such as we expected to see. And the mess only gets worse from there…

2. Barber Institute of Fine Arts B0005 & B0006 (Anastasius I, Constantinople, officinae Eta and Iota), B2761 & B2762 (Heraclius, Constantinople, both officina Eta), B4384 & B4385 (first reign of Justinian II, Constantinople, former marked Theta), B4464 & B4465 (second reign of Justinian II, Constantinople, no control marks), B4598 & B4599 (Constantine VI and Eirini, Constantinople, no control marks).

3. Those earlier analyses being principally those gathered and conducted in Cécile Morrisson, Jean-Noël Barrandon & Jacques Poirier, “La monnaie d’or byzantine à Constantinople : purification et modes d’altérations (491-1354)” in Morrisson, Claude Brenot, Jean-Pierre Callu, Barrandon, Poirier & Robert Halleux, L’or monnayé I : purification et altérations de Rome à Byzance, Cahiers Ernest Babelon 2 (Paris 1985), pp. 113-187.

4. The kind of conclusions, indeed, that were coming out of ibid. and another study there, Jean-Pierre Callu, Claude Brenot, Jean-Noël Barrandon and Jacques Poirier, ‘”Aureus obryziacus”‘, ibid. pp. 81-111, albeit with a rather more variable sample of evidence!

Announcing All That Glitters

Starting work at the Barber Institute in August meant learning to work in and outside of office hours again, and I’m still rebalancing my routine. It has also meant an even longer to-do list, not least since I am also still doing some teaching for History at Birmingham on my spare day. There are long and difficult jobs connected with the electronic catalogue of the coins and the numismatic library, as well as more immediate ones connected with the next exhibition. But it has also meant a bunch of exciting new research projects! In some ways this should have been expected, and indeed I came into the job with one particular problem I wanted to use the coin collection to address, which I’ll tell you about when I’m slightly further along. But in the meantime, we are about to start something quite big and I wanted to announce it. The project name is “All that Glitters: the Byzantine solidus 307-1092″, and it aims to carry out non-destructive scientific testing of the metal composition of the Byzantine gold coinage over that period, up to 300 coins in all depending on results.

A gold solidus of Emperor Anastasius (491-518) struck in Constantinople, Barber Institute of Fine Arts B0031

A gold solidus of Emperor Anastasius (491-518) struck in Constantinople, Barber Institute of Fine Arts B0031

The reason this has got so ambitious is that word ‘we’, because this is essentially the brainchild of Rebecca Darley, one of the curators of the current coin exhibition at the Barber as you may remember and now part of the Bilderfahrzeuge project based at the Warburg Institute in London. Rebecca is an energising collaborator who does not think small and has thus gathered me, as the man with the coins and the wider medieval background, and Robert Bracey of the British Museum, as a man with an X-ray flourescence spectrometer and experience using it on the money of ancient empires, into a suddenly-active attempt involving Birmingham University’s School of Chemistry and Bruker Industries Ltd., who make XRF machinery among many other things, to deepen the basis of Byzantine monetary history (and with that, it’s probably not too much to say, the monetary history of the early Middle Ages as a whole). Here is our synopsis, with some edits for context:

“The Byzantine Empire, which evolved from the eastern Roman Empire, issued coinage continuously for more than a thousand years. The gold solidus, a coin of 4·5 g and a notional 95-97% purity, was the backbone of this system from the reign of Emperor Constantine I (306-37) to the eleventh century, though it was debased steadily from the tenth century until its replacement in a coinage reform in 1092. Before that time, the reputation of the solidus was near-legendary and it has remained so in scholarship.” In fact, however, we have limited evidence as to the precise purity or composition of the early coinage prior to debasement.
Earlier metallurgical studies of Byzantine gold coinages concentrated mainly on the later period, and used the most sophisticated equipment available in the 1980s and 1990s. Recent developments in X-Ray Flourescence technology, in which Bruker Industries Ltd. have been at the forefront, now make it possible to evaluate non-destructively the composition of metal alloys with far greater sensitivity to a range of trace elements, and the ability to quantify very small changes in the proportions of different metals in an alloy and in detecting and identifying even minute quantities of trace elements. “These newly developed techniques have not, however, been applied to Byzantine gold coinage and the time is therefore ripe for a project which could not only offer new data on the Byzantine monetary economy but also explore the possibilities of XRF testing, and set standards of analysis for other currencies and precious-metal objects.
“The Barber Institute of Fine Arts contains the most important collection of Byzantine coins in Europe and its greatest strength is in the coinage of the sixth to eighth centuries. It is currently unpublished, though cataloguing is in progress, and it has never been subject to any metallurgic analysis. It therefore offers an entirely new source of data for a detailed examination of the gold coinage that underpinned the Byzantine economy. In light of increasing recognition by historians that the numerous crises experienced by the Empire were survived only because of the sophistication and resilience of the imperial monetary and taxation system (Haldon, 1990; Wickham, 2005; Brubaker and Haldon, 2011), this study has immediate relevance not just to the Middle Ages but also to wider questions about the impact of monetary stability on political balance.”

You see that we have plans, and as of last week, we now have permission from the Henry Barber Trust, who own the collections of the Barber Institute, to carry on and do Science! with their coins. At this point we’re still in meetings-and-planning stages but before the end of the year we will in fact be zapping solidi with X-rays and trying to get money from people to do so on a rather larger scale. We should be presenting preliminary results from the first phase of work as early as January. It’s all moving rather fast! Anyway. One of our pledges is to keep the world updated via our various blogs, but I rather thought you might be interested anyway. Now, when those results come in, you’ll have some idea of what they might lead to…


The references above decode as John Haldon, Byzantium in the Seventh Century (Cambridge 1990); Chris Wickham, Framing the Early Middle Ages: Europe and the Mediterranean 400-800 (Oxford 2005); and Leslie Brubaker & John Haldon, Byzantium in the Iconoclast Era c. 680-850: a history (Cambridge 2011). To those I should add the essential starting point for the scientific study of Byzantine coinage till now, Cécile Morrisson, C. Brenot, J. N. Barrandon, J. P. Callu, J. Poirier & R. Halleux, L’or monnayé I : Purification et altérations de Rome à Byzance (Paris 1985).