Testing, Testing! X-Rays Help With Find Identification
[The Searcher, August 2009, Page 28]
by Brett Hammond of TimeLine Originals
It has been a long day. You have dragged your detector and finds box around a corner of a promising field for hours, and returned to your vehicle for the long drive home. The items you have collected look promising – some coins, some metallic blobs, a fragment of a brooch, perhaps some interestingly shaped pieces of metal. Once home, rested and refreshed with tea, you spread your cache of goodies out on the kitchen table to begin the process of cleaning them, and working out what exactly you have found.
Down from the shelf come the well-worn reference books, the back-issues of “The Searcher” and old copies of “Detector Finds”. A quick sort into ‘coins’, ‘buttons’, ‘musket balls’ and ‘unknown’ allows you to pick out the commoner types of finds, the ones you have seen before and you were perhaps expecting to collect on the site. But what about the others? Where do you start with that flat frilly-edged piece of metal? Is it a Roman belt-fitting, part of a medieval brooch, a Saxon wrist-clasp or the clip off a Victorian tea-caddy? Hours of poring over the artefact guides offer some possibilities – but you don’t want ‘possibilities’, you want to know what it is with a better degree of certainty.
Until quite recently, your only guide was ‘shape and size’ along with your intuition based on personal experience. ‘If it looks and feels like a Roman propeller fitting, that’s good enough for me.’ But really this isn’t good enough. You can’t be sure that you made the correct identification in the first place, and you can’t then be sure about ‘authenticity’.
For one thing the object might be a copy – the audacious counterfeiting operation of the Victorian Shadwell forgers William Smith and Charles Eaton (Billy and Charley) is well known and their artefacts have become collectible in their own right. Modern copies of ancient objects can be found at any re-enactment event or fine-art fair.
With the growth of tourism and foreign holidays in the later 20th century, a lot of modern reproductions of ancient brooches and jewellery are in circulation, brought back by holidaymakers and then lost. These ‘tourist pieces’ are bought precisely because they look old and interesting, and they can be very difficult to identify for this reason. More likely, the item will be incomplete, perhaps damaged and looking a bit sorry for itself. It will need a little tender loving care and a lot of work in a library to take the story further forward.
The piece might even be an ancient ‘fake’ – counterfeit coins are not a new idea! The Romans also took to replicating ancient artefacts in a big way – Greek and Egyptian statues and dress accessories, for example. One new and invaluable weapon in the detector’s and collector’s armoury involves the scientific analysis of metal. This is the technique that has been used to spot deliberate fakes – gold rings offered for sale as Roman, Saxon or mediaeval but made from modern 9 carat gold are one obvious example. There are several techniques which can be used to analyse metal content, but most of them have the twin disadvantages of being (i) destructive to the object and (ii) eye-wateringly expensive. Fortunately, modern technical advances in miniaturization and new applications of the atomic chemistry of metals have brought the process of X-Ray Fluorescence (XRF) testing to the detector market.
The first point about XRF antiquity testing is that it does no damage to the object being tested. The item does not need to be prepared in any way, does not have to be put into a vacuum or have its surface patina disturbed. The XRF machine fires a highly focussed X-ray onto the object’s surface. This causes the metal to fluoresce (glow) and the precise characteristics of the fluorescence make it possible for the elements present to be detected. The X-ray disturbance is at the sub-atomic level across a small portion (a few millimetres) of the surface and is totally invisible. The process is also very fast – results can be displayed on the machine’s screen within a few minutes.
These factors – no need for preparation and fast read-out of results – mean that the cost of this process has come down enormously in recent years and this in turn has allowed new companies such as Oxford X-ray Fluorescence to make the service available to the public at an affordable price.
What are the limitations of XRF testing? As we just described it, it will be obvious that the process only tests the surface of the object (with penetration of a just a few atoms!) so items with a perfect gilded surface can only be tested for the quality of the gold. But most metal-detected antiquities have been in the plough-soil for a good while before they are found so the gilding, tinning or other surface treatment has usually rubbed off some areas. Also, gilding tends to be applied only to the obverse of an object, with the reverse left plain as it will never be seen. In most cases it will be possible for an analysis of several parts to be made. And of course gilding can tell its own story – the quality of some Anglo-Saxon mercury gilding is amazing compared to the later mediaeval results.
Can XRF testing authenticate objects? The honest answer is that by itself it cannot. The test results have to be interpreted. The technicians at Oxford X-ray Fluorescence have to take the results of the analysis and compare them with results from known genuine objects to evaluate them. Even then all that can be said is that an object’s composition is ‘consistent with’ objects from a certain date-range. Most importantly the process can instantly identify all but the cleverest fakes and the most faithful copies.
But for the finder, knowing that the object is 95% consistent with a Late Roman or a Middle-Saxon date is enough – art styles, artefact typologies and other techniques will tell the rest of the tale. The research and identification process contributes to the satisfaction of finding and owning an ancient object. The XRF test for antiquities is helpful, fast and a cost-effective means of taking a large part of the guesswork out of this. Oxford X-ray Fluorescence Ltd can be found at http://oxford-labs.com and contacted by email firstname.lastname@example.org.
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