Tag Archives: Robert Bracey

Chronicle III: January to March 2016

I’m sorry there was no blog last weekend. Frustratingly, the thing I spent that time on now isn’t going to work out, so I’m determined to make sure there is a post this weekend, and the post that is due is the next round-up of my academic life, which has now reached 2016. It has been five months since I posted the last of these three-month slices, and the only real consolation there is that it took me less time to get through those three months of blog content than it did the previous one, but we will hopefully still see further gains made as marking ebbs and the summer shapes up. Can but hope, eh? But meanwhile, here’s how it looked at the beginning of 2016 for your humble blogger.

Teaching

It’s not just tradition but also a reflection of the real state of life that the first item on the bill is always teaching. Actually, in the first half of 2016 I had a lower teaching load than I have had since or likely ever will at Leeds, given what they need me to cover; I was running one module, albeit a big one, and contributing bits to a couple of others. That said, the beginning of the semester was still a fairly steep learning curve, as the module I was running was an inherited first-year course called Empire and Aftermath: The Mediterranean World from the Second to the Eighth Centuries, and even my undergraduate study experience only previously went back to AD 284; I’d never done the second or third centuries before in any context, let alone one where I needed to show expertise. Thankfully I had the help of two postgraduates who’d taught the module before and that made everything easier, although I did also have to second-mark and observe those postgraduates so they were not solely a labour relief. It was all a fair bit of work, and it coincided with the early part of the excellent but intensive Palaeography: Reading Medieval Manuscripts that we put our MA students through, which has continuous assessment. Furthermore, Leeds has examinations on the first semester’s modules as soon as the students get back in January, so I was reading up for the new stuff and choosing manuscript images for palæography at the same time as marking these exam scripts, and by the time I was done with those the first palæography assignments were in, and they were only just back to the students by the time the first-years’ formative essays came in, alongside the second palæography assignments… and in general it seemed a long time before the marking stopped.

Wolfenbüttel MS Codex Guelfybertiani 13, fo. 6v

One that was set; can you read this? Come to Leeds and we’ll teach you! But if you want to know more independently, it is Wolfenbüttel MS Codex Guelfybertiani 13, folio 6 verso, and you can find out more via the link through the image

In between these I fitted a couple of workshops for an Institute for Medieval Studies module, Medieval Narratives on the Modern World, on European national origin myths and on the so-called Reconquista, but those were fun and much less work. And there were also personal tutorials to be fitted in, to which only half the students turn up but of course you must book the time anyway, and feedback meetings, and also joint care of a visiting Chinese Ph. D. student. I felt fairly busy. Still, looking back, I was not carrying very much and the next year would have been much harder if I hadn’t had this run-up.

Extra Labours

That must also be how I had time for the other things I was doing. In particular, having found out that there was this coin collection in the bottom of the Library, I had resolved to make it part of my teaching, and so one of the few changes I did make to Empire and Aftermath was to turn one of the seminars into a coin-handling session to try and get people excited about the reality of the period in their hands. I’m not sure how well that worked, though commendably both my postgrad assistants leapt at the chance to be able to say they’d taught with coins and did some crash-course Roman numismatics with me, which made me feel useful. More prosaically, in the state of the collection there wasn’t really a way to find out what there was to teach with except to inventory it, so I put aside my Friday afternoons for most of this period to inventory the medieval, Byzantine and late Roman coins and got through a fair few. Some day soon I will get round to sorting out the photographs I took of the cool ones…

Copper-alloy 40-nummi of Emperor Constans II overstruck at Constantinople in 641-642 on a coin of Emperor Heraclius, DOC II Constans II 59c, Leeds, Brotherton Library, uncatalogued

Here is one that perhaps only I could think is cool, a horribly-made copper-alloy 40-nummi of Emperor Constans II overstruck at Constantinople in 641-642 on a coin of Emperor Heraclius, DOC II Constans II 59c, Leeds, Brotherton Library, uncatalogued

There was also other stuff involving coins. Back at the Barber Institute the process of replacing me had unfortunately crossed with their normal exhibition schedule, so my humble effort, Inheriting Rome, was extended for a few months to give the new curator a chance. I got to see my thus-prolonged exhibition again because there were still two more sessions of the now-legendary All That Glitters project to do, about which I will tell you shortly, and of course back at Leeds this was also the time in which I started the wheels turning on the project that would become Unlocking the Winchester Cabinet. My head of department was actually concerned that I was going to spend all my time doing late antique numismatics and not the research on whose basis I’d been hired, which I didn’t see as a serious worry because, at this point, there was still time and I used it on stuff that was interesting and useful for others as well as for me.

Other people’s work

I was also at this point still managing to travel for seminars a bit, and I have a lot of notes from this period that I’m not really going to say much more about. The itinerary looked like this, though:

  • Katherine Cross, Dominic Dalglish and Robert Bracey, “Images, Relics and Altars: comparing material religion on the first millennium”, Earlier Middle Ages Seminar, Institute of Historical Research, University of London, 20th January 2016, to which I went mainly because Robert is an All That Glitters collaborator, but at this stage he was also busy with a project called Empires of Faith, which was doing the kind of cross-cultural comparison implied by their title here, with Katy Cross bringing early English Christian monuments like the Gosforth Cross to the table, Dominic Dalglish coming from the ancient Mediterranean world and Robert from Kushan India, but here talking as much about what made for valid comparison in this set-up as the actual objects. This was interesting but the results of the project can now be investigated on the web, so I’ll leave this one aside and move on to…
  • Hugh Kennedy, “ISIS and the Early Caliphate”, Centre for the Study of the Middle Ages Annual Public Lecture, University of Birmingham, 27th January 2016, to which I travelled down and which I thoroughly enjoyed, but which needs treatment together with…
  • Julia McClure, “A New Politics of the Middle Ages: a global Middle Ages for a global modernity”, Medieval History Seminar, University of Leeds, 3rd February 2016, also substantially about the way people were reading the Middle Ages into the situation in the Middle East at that time, but approaching it from a very different direction. So I’ll do a post about those two together.
  • I also made it down to London for Alex Rodríguez Suárez, “The Komnenian Emperors: a Latinophone dynasty”, Earlier Middle Ages Seminar, Institute of Historical Research, University of London, 11th February 2016, about the extent of the changes brought about in Byzantine court ceremonial under, especially, Manuel I Komnenos that would be attributed to Latin influence, which Dr Rodríguez wanted, I think rightly, to read as appropriation of ways to assert dominance over the new Latin lords in the Middle East, not an aping of their flashy chivalric habits as they have often carelessly been read. That seemed convincing to me but I don’t have much more to say about it, so on to a clutch of things back at Leeds, as follows:
  • Pat Cullum, “‘Looking the Part’: presentation and representation of clerical masculinity in late medieval England”, Medieval History Seminar, University of Leeds, 24th February 2016;
  • Esther Eidinow, “Seeing into the Future? Oracles and the Ancient Greeks”, Classics Seminar, University of Leeds, 25th February 2016, about ancient Greek stories in which oracles were tested before being consulted for real, pushing at the edges of our categories of rational and irrational, interesting and my first step in a plan to make friends with my counterparts in Classics and Ancient History;
  • Natalie Anderson, “Tournament Trappings: Textiles and Armour Working Together in the Late Medieval Joust”, Medieval Group Seminar, University of Leeds, 7th March 2016, the culminating presentation by one of our Ph.D. students then about to finish and very much a mature piece of work about the ways in which combatants in late medieval tournaments displayed and distinguished themselves, which was as much or more a matter of fabric as the armour that more often now remains to us.
  • Then, back to London again to see a big name, Philippe Buc, “Eschatology, War and Peace: of Christ’s Armies, Antichrist and the End of Times between ca. 1095 and ca. 1170″, Earlier Middle Ages Seminar, Institute of Historical Research, University of London, 10th March 2016, arguing for a change in the way that medieval people thought about the oncoming end of the world that occurred with Crusading, in which it becoming OK to kill for God was itself a sign of the end times, but one that could last for quite a long while, setting up the fight that would now go on until everyone was Christian and the End finally came. I remember this being fun and extremely erudite, but looking back over my notes I’m not sure what I have to add to that summary, so it’s back to Leeds for two more to close the season, the relevant items being:
  • Travelling the World: from Apuleius to the Icelandic Sagas, from the picaresque novel to travel literature, a more substantial seminar in Classics whose separate components were:
    • Regine May, “Travelling to the Land of Witches: Apuleius’s Golden Ass“, about Thessaly’s Classical reputation as a hotbed of magic and sorcery and how travel might thus lead you out of the known world in several dimensions, and
    • Ros Brown-Grant, “Encounters between the East and West in Fifteenth-Century Manuscript Cultures”, on pictures of Westerners meeting Easterners either in West of East as imagined by Western manuscript artists, usually for tales of betrayal where Greeks were concerned or conversion where Muslims were, sort of inevitably.
  • and finally, Ross Balzaretti, “Early Medieval Charters as Evidence for Land Management Practices”, Medieval History Seminar, University of Leeds, 16th March 2016, to which I would have gone even had it been further afield since Ross has been a supporter of mine for a long time and I am very interested in his work, but precisely because it’s quite similar to my own, I’m not going to do a detailed write-up here because it would look a lot like, “Ross’s charters say things like mine do!” It was good, but you can already read the same sort of thing here.

My Own Research?

So that brings us to the end of the timespan, and I have only promised three extra posts out of it this time, though actually there are also one news and two tourism posts that should also be fitted in there. But what is as ever missing is my own research. What was I working on in this period, looking back? Well, for one thing I was finishing revisions on the conference paper that nearly wasn’t, “A Problem of Concavity”; the final version of that was fired off into what became a suspicious silence in the middle of February 2016. After that I seem to have turned to the reading to support the revision of my venerable paper on early medieval crop yields, of which I’d done the bulk while still at Birmingham, and I had a new draft of that done in March, although, it would seem, not one I thought submissible; that was still a way off, and I now don’t recall why. But beyond that it’s hard to see what I was doing, and the conclusion has to be, I think, that despite the apparently light load I was struggling. I would build up academic muscle from here, and reluctantly trim back a lot of the activity above to make other things possible, but at this stage I was still enjoying being an established academic as I’d imagined it and seen it done by others, as well as reading a lot for teaching, and perhaps not getting that balance entirely right, in retrospect. I think, also, I still hadn’t actually worked out how to schedule research in a job that finally actually included that as a duty, but had structured time only for other activities. Actually accepting that it was a legitimate use of my employers’ time to read a book, after years governed by the next deadline, was still proving weirdly hard for me… Of course, I still was governed by the next deadline, functionally, but I was only letting others set them, wherein a mistake with future complications. Anyway, this story will be continued! But for now there’s enough queued up to write about, and this has already been a long post, so I’ll wrap it here and thank you for reading.

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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).