Tag Archives: metallurgy

Conferring over coins in Birmingham

Sorry about the lateness of this post; I write between two family gatherings that have taken up quite a lot of writing time. But here is a post even so! We’ve come so far with the whole world situation that people are contemplating having real in-person conferences again, but this post is still a story of the distant past for now, and specifically of 18th November 2017, when I was down in Birmingham and indeed my old place of employ, the Barber Institute of Fine Arts, to listen to a conference about the collection I briefly managed, entitled ‘The Barber Coin Collection Colloquium Day: Past, Present and Future Research’. I didn’t speak at this myself, being somewhat embroiled with other work just then, but I learnt a few things by going. These were the speakers:

  • Margaret Mullett, “The Legacy of Anthony Bryer”
  • Rebecca Darley, “Sri Lankan Coins in the Barber Collection”
  • Maria Vrij, “How Do You Solve a Problem Like Mezezios?”
  • Wei-Sheng Lin, “Armenian Cilician Coinage”
  • K. MacDonald, “African Gold Sources for Byzantine Carthaginian Coins”
  • Anika Asp, “Numismatic Sources for the Empire of Trebizond”
  • Alex Feldman, “Coinage and Commonwealth, 9th-11th Centuries: local dynasties and mints in the ‘Ummā and Oikoumene”
  • Joseph Parsonage, “Coins and Co-Emperors – Crowned Regents in Byzantium”
  • Michael Burling, “Sasanian Numismatic Imagery and its Influence”

Now, of these, Wei, Alex, Joseph and Mike were at that stage various levels of postgraduate at Birmingham and were not primarily working on coins for their theses, and had really been introduced to them either by me or Maria as Curators, so they were presenting partly for practice and partly out of goodwill, and for that reason I shan’t discuss their papers in any detail. Professor Mullett’s presentation, in turn, was largely a biographical sketch of a man who had been involved in the negotiations that led to many of the collection items being in the Barber at all, and you can read about him in more detail yourselves if you like. So that leaves Rebecca, Maria and Dr MacDonald, all of whom had things to say which are still probably interesting if you’re interested in such things!

Gold imitation of a solidus of Emperor Theodosius II possibly made in India or Sri Lanka, Birmingham, Barber Institute of Fine Arts LR0482

Gold imitation of a solidus of Emperor Theodosius II possibly made in India or Sri Lanka after 402 CE, Birmingham, Barber Institute of Fine Arts LR0482

Rebecca’s paper was an analysis of the sale history of five late-Roman-or-Byzantine coins which, according to a note lurking in the Barber’s archives, had been found in Sri Lanka. This seemed, on the face of it, dubious. Now, not many people have a better idea of what imperial numismatic material is found in Sri Lanka, and as we’ve seen Rebecca also knows a thing or two about numismatic collectors. A false hope was realised by the possible connection of two of the coins to one Leslie de Saram, a man famous in Lankan archaeology but who nonetheless acquired pretty much all his coins on the London market; but the coin above, as well as one of Maurice, she thought could possibly be Sri Lankan finds given everything recorded about them in the Barber (not much) and the wider finds patterns, though even there the Maurice coin would fill a gap rather than having parallels.1 It makes me suddenly think that if our failed attempts to get through the surface dirt on these coins with an X-ray had in fact been directed at analysing the dirt, maybe we’d have been able to settle this question! But as it is, it is still a matter of possibility whether the Barber does in fact hold coins that went all that way out of the Empire and then had another Empire bring them back again and out the other side…2

Gold solidus of Emperor Constants II struck at Carthage 641-654 CE, Birmingham, Barber Institute of Fine Arts B4100

Gold solidus of Emperor Constans II struck at Carthage 641-654 CE, Birmingham, Barber Institute of Fine Arts B4100, tested in the All the Glitters project and not found wanting

Since we’re now talking about metals analysis, it probably makes sense to discuss Dr MacDonald’s paper next. This was coming out of a project that was trying, effectively, to work out when and if trade across the Sahara Desert can be archaeologically documented before the Islamic era. Part of this work had involved trying to work out if sub-Saharan gold had reached the north of Africa before that time, and one way to determine this was to test coinage issued in Byzantine Carthage, of which of course the Barber has a bit (and we tested some). The thing here is that Byzantine coins from Carthage took on an increasingly thick, globular aspect over the sixth century, as you can sort of see above, and it has been suggested that this is because the blanks were coming in as lumps from the Essouk goldfields, way way south, because such lumps have been found as production debris there.3 Somehow I didn’t write down what methods Dr MacDonald was using to test his coins, but the methods must have been better than ours as he was finding distinct differences between the normal, flat solidi previously minted by Carthage and the globular ones which did not themselves prove, but were consistent with, the idea of them being on Essouk blanks, and what the difference largely was was that the globular coins were made out of unrefined gold. I would have to say that this didn’t fit with what we’d found when we’d tested one, but then as we know our methods were not very good. This is why I (still) want to know more about his…

Gold solidus probably struck by Emperor Mezezios in Syracuse 668 CE, Birmingham, Barber Institute of Fine Arts B4272

Gold solidus probably struck by Emperor Mezezios in Syracuse 668 CE, Birmingham, Barber Institute of Fine Arts B4272

Lastly, here if not on the day, Maria’s paper covered a very rare coin of which the Barber has one, apparently struck by a very short-lived usurper—I suppose if he’d been long-lived we’d just call him an emperor—by the name of Mezezios, who rose up in Sicily in 668 after the murder of Emperor Constans II. His coinage was first identified in 1979, but has been disputed ever since, and while Maria did not claim to have solved the problem herself, she did, by explaining the arguments for and against, make it seem much more likely that such a thing would have existed, and therefore that since there are several known from different contexts, they’re probably that thing. The argument really hinges on the fact that, iconographically, the coins appear to imitate those of Emperor Justinian I, from a century before, rather than anyone more recent, and while this has a been a mark against the theory for some people Maria thought, quite reasonably I reckon, that if you’re usurping the throne from a dynasty you don’t borrow their iconography, but go back to before their problem ever arose. Certainly this happens with those who finally did, temporarily, replace that dynasty by overthrowing Justinian II and reversed his numismatic innovations, so I don’t have a problem with it thirty years before either!4

All things considered, this was a good thing to have been part of. It did what I think Maria had hoped, by demonstrating that having a good collection in a university can actually be a generator of research and that that research, even on tiny things like coins, can open up bigger findings. It is necessary to remind people of this, every now and then, and while I’m not sure the people who most needed to know it were there, at least by writing it up, even this late on, I can help to remind a few more people of this significant truth!

1. That Maurice coin is Birmingham, Barber Institute of Fine Arts, B1767, visible here.

2. Rebecca now has a version of this story in print, and indeed online, as Rebecca Darley, “‘Implicit Cosmopolitanism’ and the Commercial Role of Ancient Lanka’ in Zoltán Biedermann and Alan Strathern (edd.), Sri Lanka at the Crossroads of History (London 2017), online here, pp. 44–65 at pp. 51-56.

3. Dr MacDonald cited what had then just emerged as David W. Phillipson, “Trans-Saharan Gold Trade and Byzantine Coinage” in Antiquaries Journal Vol. 97 (London 2017), pp. 145–169, online here.

4. My bit of that is due soon to emerge as part of Jonathan Jarrett, “Coinage in the Western World at the End of the Roman Empire and After: Tradition, Imitation and Innovation” in Journal of Ancient Civilizations Vol. 36 (forthcoming). You will hear here when that happens!

All That Glitters, Experiment 6 and final

So, as just described, almost my first academic action of 2016 – for that is how far in the past we are for this post – was to head back to Birmingham, freshly remobilised, to pursue what was supposed to be the last run of experiments in the All That Glitters project of which I have now told you so much. Since the last one of those posts was only a short while ago, I’ll not reprise the project plan beyond saying it was to try and find out what was in Byzantine gold coins besides gold using X-ray fluorescence spectrometry and we were finding it difficult to get beyond what was on Byzantine gold coins. Now, read on!

Gold solidus of Emperor Constantine VI and Empress Eirini, Barber Institute of Fine Arts B4599

Gold solidus of Emperor Constantine VI and Empress Eirini, Barber Institute of Fine Arts B4599, in XRF analysis sample cup

Since we now more or less had a working method established, if it could be called that (since it didn’t really work), we had decided that our original research goal, of spotting changes in the trace elements in the centrally-minted gold coinage of the Byzantine Empire, was beyond the technology, and we needed to work out what else we could do with the remaining machine time. At first we’d thought we wouldn’t have enough, now we had more than we knew what to do with… But the most obvious thing seemed to be to broaden our sample as much as possible. So, we selected more of the Barber Institute’s coins, taken from imperial reigns we hadn’t covered, extra denominations from ones we had and sets from other mints than Constantinople that we could compare to coins of the same emperors there, and we took them all over to University of Birmingham’s School of Chemistry over a period of four days, where we were as usual excellently looked after as far as they could manage, and we subjected them to analysis. In all of this we were hampered by the fact that results were basically hard to reproduce; in fact, this became so frustrating that when it became clear that we still had a dribble of machine time budget left at the end of these experiments, we set up one more to address that problem specifically, and that will be the last of these posts when I get so far. But for this one I can basically give you only a very simplified set of findings, some of which might address real questions if only we could trust our results, and then gently suggest that even what we did get might justify some careful conclusions, though they might not really have justified the labour. So: some late antique numismatic questions, as answered by the S8TIGER in January 2016!

Bruker S8 TIGER XRF analyser open for business

Our tool of analysis, the S8TIGER WD-XRF machine, ready for action

Our first question in this set of tests was about fractional denominations. Though the primary imperial gold coin was the famous solidus, the “dollar of the Middle Ages”, there were also small numbers of halves (semisses) and thirds (tremisses) struck, with slightly different designs.1 Were these actually struck from the same metal as the solidi? Our results, shaky as they were, suggested that the answer was broadly ‘yes’, at least at Constantinople and, as far as we could test, Carthage. The only place where we picked up any reasonably substantial difference was Syracuse, in Sicily, but we’ll come back to that…

Gold solidus of Emperor Maurice struck at Ravenna 582-602, Barber Institute of Fine Arts B2390

Gold solidus of Emperor Maurice struck at Ravenna 582-602, Barber Institute of Fine Arts B2390

Gold tremissis of Emperor Maurice struck at Ravenna 582-602, Barber Institute of Fine Arts B2391

Gold tremissis of Emperor Maurice struck at Ravenna 582-602, Barber Institute of Fine Arts B2391; note the different design

The other thing we were hoping to establish in this set of tests was variations between mints. I admit that I was cynical about this; as I think I’ve said before, it had sort of become clear that almost all the elements were shared, and that this made sense in a world where imperial coin was being sucked into Constantinople in tax from right across the Mediterranean each year, melted down and then returned to the world as new coins; the recycling should have mixed everything together over time.2 So the only place we had a hope of seeing such variation was in places where that centralisation was breaking down, and in fact, from very early on it had become clear that late coins of Syracuse were gold-poorer than their Constantinpolitan contemporaries, to the extent where the one of us who hadn’t loaded a coin, so didn’t know what it was, could still tell if it was a Syracusan one from its results.

Graph of gold content over time for Byzantine mints of Constantinople and Syracuse

A very rough Excel-generated graph of coins’ gold content over time for the mints of Constantinople and Syracuse, by your humble author

Some of that impurity was visible by eye, indeed, but we could pick it up from before that. Indeed, there are one or two problem cases where mint attribution is uncertain for such coins, and for one of those at least, we were pretty sure we could now partly answer the question.3

Powerpoint slide showing three tremisses of Emperors Leo III and Constantine V from different mints

This is a slide I’ve grabbed from a presentation I will come to tell you more about in Princeton, and it’s the one on the right that’s the undecided case; but its metal content is much more Italian than Constantinopolitan, and we might get further yet

Why Syracuse was allowed to run its coins differently is a separate question, since as far as we know it was still paying tax to the centre and its coins must have been detectably poorer there too, but maybe what we’re seeing here is actually proof that it didn’t pay tax; its small change, too, seems to have been treated in such a way as to restrict its circulation, and Rebecca Darley (I can take no credit for this thought) wondered therefore if Sicily was persistent suffering a currency drain to the East that these measures were meant to stop by deprecating the exchangeability of Sicilian money.4 It might have helped!

Scatter plot of silver content versus copper content of Italian-attributed Middle Byzantine coins

Scatter plot of silver content versus copper content of Italian-attributed Middle Byzantine coins, which is probably Maria Vrij’s work, though I don’t remember; it was certainly her idea to do it

But as it turned out, we could get one step further with such distinctions. One of the other enigmas about coinage in Byzantine Italy is that we’re not totally sure which issues belong at which mints. Syracuse’s particular characteristics become distinctive after a while, but there are a rook of issues which are tentatively attributed to Ravenna, Rome or just ‘Italy’ that no-one’s really sure about.5 We haven’t solved this problem, but we may have spotted something that will help with it. I say ‘we’, but just as I owed the previous point to Rebecca Darley, this one was thought of by Maria Vrij; I sometimes think my sole intellectual contribution to this project was mainly defeatism. Maria noticed that whereas the Syracuse coins were debased with both silver and copper, and thus maintained a ruddy gold colour even once quite poor-quality, the elemental profile we were getting from supposed Ravenna issues included nothing like as much copper. Instead, the Ravenna issues seem to have turned ‘pale’, being adulerated only with silver. In that respect, they were following the trend of the post-Roman West at large, but it also makes sense in its own terms: Ravenna issued silver coin, which Syracuse didn’t, so when they had to cut corners with the solidi it makes sense that it was the refined silver from the local coinage that went into the pot, while Syracuse was presumably using less processed metal with accompanying copper content.6 So that’s something that belongs to Maria to write up properly, but hopefully it won’t be as many years before that happens as it has already been since we found it out… I make no promises there, as we all have other priorities, but nonetheless, we did find stuff in these tests that people might want to be able to refer to, and I hope this write-up at least gives some basis to believe that!

1. If you want the basics on these coinages, you can do no better even now than consult Philip Grierson, Byzantine Coins (London 1982), where pp. 50-56 will cover you for these purposes. The catchphrase, though, comes from Robert Sabatino Lopez, “The Dollar of the Middle Ages” in Journal of Economic History Vol. 11 (Cambridge 1951), pp. 209–234, online at http://www.jstor.org/stable/2113933.

2. My picture of this process comes pretty much direct from M. F. Hendy, “Aspects of Coin Production and Fiscal Administration in the Late Roman and Early Byzantine Period” in Numismatic Chronicle 7th Series Vol. 12 (London 1972), pp. 117–139, which is clearer than his later treatment in Michael Hendy, Studies in the Byzantine Monetary Economy, c.300-1450 (Cambridge 1985), pp. 257-303.

3. The standard reference for such matters, Philip Grierson, Catalogue of the Byzantine Coins in the Dumbarton Oaks Collection and in the Whittemore Collection, volume three: Leo III to Nicephorus III, 717—1081 (Washington DC 1973), Part I, where the coins in question are listed under Leo III 18a.1 (the Barber’s specimen online here), 48 (the Barber’s specimen online here) and, maybe, 12, 13 or 42 depending on what the Barber’s specimen (online here) actually is; the metallurgy makes type 42 seem likely though!

4. On the relevant Sicilian small change see for basics Grierson, Byzantine Coins, pp. 166-168, but for a different view of what was going on with its currency see Cécile Morrisson, “Nouvelles recherches sur l’histoire monétaire byzantine : évolution comparée de la monnaie d’or à Constantinople et dans les provinces d’Afrique et de Sicile” in Jahrbuch der österreichischen Byzantinistik Vol. 33 (Wien 1983), pp. 267-286, repr. in Morrisson, Monnaie et finances à Byzance : Analyses et techniques, Collected Studies 461 (Aldershot 1994), chapter X.

5. Grierson, Byzantine Coins, pp. 168-171.

6. Ravenna’s silver is discussed ibid., p. 140, but for the bigger picture see Mark Blackburn, “Money and Coinage” in Paul Fouracre (ed.), The New Cambridge Medieval History volume I c. 500‒c. 700 (Cambridge 2005), pp. 660–674.

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!

An awful lot of numismatists in Sicily, II

So, after that bit of numismatic self-congratulation, let me take you back for the last time to September 2015 and the town of Taormina in Sicily, where I was then one of many gathered for the 15th International Numismatic Congress. You’ve seen some of the local antiquities, heard about the first two-and-a-half days of papers and visited a local castle, now it’s time to return to the thick of the academic fray. But first, a party!

Party in the coutryard of the Palazzo dei Duchi di Santo Stefano, Taormina, Sicily

Party in the coutryard of the Palazzo dei Duchi di Santo Stefano

Indeed, the first thing on our calendar after descending from Castelmola and eating was not an academic session but a party put on by the Medieval European Coinage project, to celebrate its resurgence into activity since the previous INC in the form of the publication of the series’ volume on the Iberian Peninsula and the near-completion of that on Northern Italy (which, much though I often doubted it, has in fact now also emerged, something I should probably announce separately too).1 By now you may well not remember that I am a part of that project still, but I am, so I was there to share in the glory. There were speeches, there was a strictly limited quantity of free wine, but mainly there was a superb setting.

Medieval European Coinage authors by the Cambridge University Press stand at a party in the Palazzo dei Duchi di Santo Stefano, Taormina, Sicily

MEC authors Bill Day Jr and Martin Allen looking very relaxed by the Cambridge University Press stand inside the Palazzo

It was a good way to wrap up the day. The next day was the last day of papers, however, and with certain obligations among them, and so for once I was up and ready right at the beginning. Here’s how it all unrolled. Continue reading

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.

‘Cooked gold’ in tenth-century Barcelona coinage: a likely correction

One of the advantages of doing scholarship on the Internet, insofar as one can, is supposed to be that you can update and correct your work. Those who like this idea seem to believe that one would never put any of one’s projects down and move on, but be happy to update them forever, rendering them forever unreliable as citations, and in general you may guess that I don’t agree that this should be the future.1 All the same, sometimes one does find something that makes one’s work look likely to be wrong and then there seems little point in not using this outlet to make that public. The unlucky victim this time is my article, “Currency change in pre-millennial Catalonia: coinage, counts and economics” in Numismatic Chronicle Vol. 169 (London 2010 for 2009), pp. 217-243, and specifically the bit of it where I discuss a particular usage of the documents from around Barcelona in the late tenth century, prices given in auro cocto, ‘cooked gold’.2 Here’s what I said in the article:

“The use of bullion was becoming more common, and the increasing incidence of qualifications like ‘bono placibile’, and in the case of the foreign mancuses, ‘chocto’, literally ‘cooked’, ‘burnt’, suggest that its standard was frequently a matter of concern.

“The term ‘chocto’ is worth a brief digression. This apparent testing or melting may have been because of a variety in standards of the gold dinars that were reaching Barcelona from various mints in al-Andalus and, probably, beyond. The origin of individual dinars is only specified in later documents, when the bulk of coin in use must have been such that such testing would have been impractical. At this early stage foreign coins may have been converted on arrival into bullion of a known standard. It is hard to read the term ‘chocto’ as referring to anything other than melting; destructive assay methods would hardly have been used on so large a scale and would, in any case, have left no minted coin with which to pay the required price.62 It may therefore be that the coins were being reminted into local versions of the mancus.63 When the supply of Islamic mancuses began to dry up in 1020, a moneyer by the name of Bonhom began to mint local ones that circulated for many years.65 The paucity of finds of imported coin of an earlier period might be explained by such a practice.”

”    63 See A. Oddy, ‘Assaying in Antiquity” in Gold Bulletin 16 (1983), pp. 52-9. I am grateful to Marcus Phillips for bringing this useful paper to my attention.
”    64 On local manufacture of mancuses elewhere see L. Ilisch, “Die imitativen Solidi mancusi. ‘Arabische’ Goldmünzen der Karolingerzeit’ in R. Cunz (ed.), Fundamenta Historiae: Geschichte im Spiegel der Numismatik und ihrer Nachbarwissenschaften. Festschrift für Niklot Kluüßdorf zum 60. Geburtstag am 10. Februar 2004 (Hanover, 2004), pp. 91–106.
”    65 On the mancuses of Bonhom and Eneas, see [Anna M.] Balaguer, Història [de la moneda dels comtats catalans (Barcelona, 1999)], 53-5 and [Miquel Crusafont, Anna M. Balaguer and Philip Grierson, Medieval European Coinage, with a Catalogue of the Coins in the Fitzwilliam Museum, Cambridge, 6: the Iberian Peninsula (Cambridge, 2013), pp. 78-81]….”

This was a sticky bit when I wrote it and looking back now the problems are even more evident. Poor-standard coins should have been more concerning once there were more of them, so why would the people of Barcelona have adopted an expensive reminting process before that point but then abandoned it? I provided an answer to this but I don’t like it, and the fact that the Bonhom mancuses survive but my notional earlier ones don’t could be just coincidence—and this whole article was after all about coins we probably don’t have—but it doesn’t make the theory any more likely. Still, in the light of what I knew it seemed like a workable answer. But then, on New Year’s Eve 2014 (because I know how to have a good time) I was reading up on the scientific study of Byzantine gold coinage for the All That Glitters project, and I found Robert Halleux getting all Greek and quoting a papyrus that contains ancient instructions for the testing of gold, in French translation which I translate as follows:

“If you want to purify gold, melt it anew or heat it, and if it is pure it keeps the same colour after being put in the fire, pure like a piece of money. If it appears more white, it contains silver; if it appears ruddier and harder, it contains copper and tin; if it is black, but pliable, it contains lead.”3

Not content with that, Halleux then quotes a [Edit: thanks to Gary for the corrected source here]letterthe Natural History of Pliny the Younger as well: “aurique experimentum ignis et, ut simili colore rubeat ignescatque et ipsum”, which is an oddly-cut quote that makes me think M. Halleux’s Latin was perhaps not so smart as his Greek in 1985. His citation certainly wasn’t, as I can find no sign of this text in Pliny, but Part of it, however, appears to mean, “gold tested in flames, both so that it shines and burns with the same colour and…”.4 Whatever M. Halleux was actually quoting, This just seems much more likely to be what is going on in my documents, testing by fire in a non-destructive way rather than actually remelting. In that case, however, it seems much less likely that the coins would have been restruck, so the Bonhom mancuses probably were the first local ones made in Barcelona.

Gold mancus of Count-Marquis Ramon Berenguer I of Barcelona (1035-76)

The Bonhom mancuses are themselves vanishingly rare, however, and there seem to be no pictures of them on the web, so, here’s a slightly later Barcelona mancus struck under Count-Marquis Ramon Berenguer I of Barcelona (1035-76), from a Cayón sale of 2009

Admittedly we still have no more sign of the actual Andalusi mancuses in the area than we do my hypothetical ones, but at least we know that the Andalusi ones did exist and that the Barcelona documents were reacting to coins we have from elsewhere.5 I don’t think it does anything serious to my overall argument in my article, either, but this alternative reading of the ‘cooked gold’ in those documents is good reason to scotch what was always one of my weaker suggestions. So let it be noted, I disavow my old idea, and I now think that that ‘cooking’ was no more than a light flame-grilling to see what colour the coin turned.

1. Compare David Parry, “Burn the Boats/Books” and Jo Guldi, “Reinventing the Academic Journal”, both in Daniel J. Cohen and Tom Scheinfeldt (edd.), Hacking the Academy: new approaches to scholarship and teaching from the digotal humanities (Ann Arbor 2013), pp. 15-18 and 19-24, both fixed texts of what were originally online presentations archived here, with Alex Sayf Cummings and Jonathan Jarrett, “Only Typing? Informal Writing, Blogging, and the Academy” in Kristen Nawrotzki & Jack Dougherty (edd.), Writing History in the Digital Age (Ann Arbor 2013), pp. 246-258.

2. J. Jarrett, “Currency change in pre-millennial Catalonia: coinage, counts and economics” in Numismatic Chronicle Vol. 169 (London 2010 for 2009), pp. 217-243 at pp. 234-235.

3. R. Halleux, “Méthodes d’essai et d’affinage des alliages aurifères dans l’Antiquité et au moyen âge” in Cécile Morrisson, Claude Brenot, Jean-Pierre Callu, Jean-Noël Barrandon, Jacques Poirier & Halleux, L’or monnayé I : purification et altérations de Rome à Byzance, Cahiers Ernest Babelon 2 (Paris 1985), pp. 39-77 at p. 40:

“Si vous voulez purifier l’or, fondez à nouveau ou chauffez, et s’il est pur il garde la même couleur après la mise au feu, pur comme une pièce de monnaie. S’il paraît plus blanc, il contient d’argent ; s’il paraît plus rude et plus dur, il contient du cuivre et de l’étain ; s’il est noir, mais mou, il contient du plomb.”

The text of reference here is Halleux’s own, R. Halleux (ed.), Papyrus de Leyden, papyrus de Stockholm : fragments de recettes. Texte établi et traduction (Paris 1981), within which the bit here cited is Papyrus Leyden X 43, but it ought also to be locatable in Earle Radcliffe Carey (trans.), “The Leyden papyrus X: an English translation with brief notes” in Journal of Chemical Education Vol. 3 (New York City 1926), pp. 1149-1166.

4. Halleux, “Méthodes d’essai”, p. 40, citing Pliny, Natural History XXXIII 59, which you can see for yourself with a slightly more comprehensible text here.

5. On the absence of actual mancuses in finds from Catalonia, see Miquel Barceló, “L’or d’al-Andalus circulant als comtats Catalans entre 967 i 1100: un or vist o no vist?” in J. M.Gurt & A. M. Balaguer (edd.), Symposium Numismatico de Barcelona I (Barcelona 1979), pp. 313-327; on the chronology of the documentary mentions see Pierre Bonnassie, “Nouveautés linguistiques et mutations économico-sociales dans la Catalogne des IXe-XIe siècles” in Michel Banniard (ed.), Langages et Peuples d’Europe : cristallisation des identités romanes et germanique. Colloque International organisé par le Centre d’Art et Civilisation Médiévale de Conques et l’Université de Toulouse-le-Mirail (Toulouse-Conques, juillet 1997), Méridiennes 5 (Toulouse 2002), pp. 47-66.

This post was written with the aid of The Bevis Frond’s White Numbers (Woronzow 2014), which has made it much more pleasant to pull together.