All that glitters…

What happens if you shoot X-Rays at coins? A question you have no doubt asked yourself often. Part of the answer was presented in the Spring of 2014 during a meeting of the Oriental Numismatic Society, held at the Ashmolean Museum.

Diagram of XRF analysis, courtesy of Bruker Industries Ltd. Click on the image for a more involved description of how XRF works!

Diagram of XRF analysis, courtesy of Bruker Industries Ltd. Click on the image for a more involved description of how XRF works!

One of the things that happens if you shoot X-Rays at a coin is that the energy from the X-Ray causes electrons in the atoms which make it up to be displaced from their orbital shells. As a result the electrons have to reshuffle to close up gaps left in the shells, and as they do this they emit energy of their own. It is a process with some interesting potential applications for numismatics. In particular, this reshuffling does not damage metals in any way, and it is possible to read the signature levels of energy being emitted by the reshuffling electrons to figure out what atom they are coming from. Theoretically it is therefore possible to read these energy emissions and establish which elements are in an object, and in what proportions they are represented, a technique of non-destructive analysis known as X-Ray Fluorescence (XRF).

At least a family resemblance...

At least a family resemblance…

S1 Titan handheld from Bruker Industries.

S1 Titan handheld from Bruker Industries.

Of couse, nothing is ever that simple. The fact that a handheld XRF machine looks an awful lot like a phaser from Star Trek does not alter the fact that pointing something at a coin and finding out exactly what it is made of is a few steps ahead of current technology. And even if it weren’t, the question of what a historian could usefully do with that information would also remain open. XRF is a technique with which a lot of good work has been done on antiquities, including coins. It is also one from which a lot of wild claims have been made, such as that it can tell us about the economic policy of ancient states or about how rich governments in the past were. Still, the series of papers about XRF at that meeting provoked the feeling that this was something which might usefully be applied to my own research area: early Byzantine gold coinage, and contemporary neighburing coinage systems.

The ONS meeting had involved a paper by a representative of Bruker Industries UK, manufacturers of a range of scientific equipment. They also sometimes make their equipment available for scholarly research as a means of testing its capabilities on different problems to those posed by industrial applications. Might they be interested in a collaboration? Another friend from numismatic/medievalist circles, Jonathan Jarrett, had recently become interim keeper of the Barber Institute of Fine Arts collection of Byzantine coins (one of the best in the world, and up to now not the subject of any scientific testing), and we had chatted about things one might research in such a collection. Also at the ONS meeting was Robert Bracey of the British Museum and another numismatist friend. Robert has undertaken XRF analysis of Kushan coins from northern India, and has an interest in the application of scientific methods to numismatics. Within a few weeks the three of us had a literature review, a project proposal and the generous collaboration of Mike Dobby and Colin Slater from Bruker UK, and Adrian Wright and Jackie Deans in the School of Chemistry at the University of Birmingham.

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Gold coin, Sind, 4th century, 7.27g (Barber Institute of Fine Arts S0074). This coin, struck in northern India, imitates Sasanian Persian coin designs of the same period. The bust depicts the Persian emperor, or King of Kings, and the design on the reverse shows a fire altar with attendants. Research questions related to this coin include whether it was made from gold with a recognisably different composition or purity from contemporary Byzantine coins, and whether any difference in composition is visible around or within the bored section in the middle of the obverse.

Initial pilot phases were carried out on 2nd and 15th December 2014. This is not the place to air initial results, especially since the main aim of our first phases was to work out some of the methodological challenges with XRF technology. The machines will churn out data, but knowing what exactly that data is and how it might or might not be applicable to historical questions is where collaboration between scientists and humanities scholars has the potential to produce meaningful answers. Some of these issues were presented at the Bilderfahrzeuge conference, ‚On the migration of images, forms and ideas‘ (13th-14th March 2015). Courtesy of (and with thanks to) the Classical Numismatic Group Roman and Byzantine Fund, administrered through the Royal Numismatic Society, we now also have money to conduct a further and more extensive round of tests in July this year, the results of which will be presented at the International Numismatic Congress (September 2015).


Dieser Eintrag wurde veröffentlicht in Bulletin von Rebecca Darley. Permanenter Link des Eintrags.

Über Rebecca Darley

I am a Research Associate with the project '"Bilderfahrzeuge" - Aby Warburg's Legacy and the Future of Iconology', based at the Warburg Institute (London). My research focuses on long-distance networks of contact in the pre-modern world, and in particular the movement of coins of the Byzantine Empire beyond imperial frontiers.

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