Taking x-rays of Roman cremation urns.
An x-ray of a Roman urn. The urn is conical, with the 'bottom' forming the point (bottom right of picture) and the 'top' being flat (although with some damage, at top left of the picture). Within the x-ray you can see a variety of fragmented bones (dense, angular white objects).
After teaching research skills to some second year diagnostic radiography students I went down to the x-ray room to meet with Dana Goodburn-Brown, an archaeological conservator. I spent the morning outlining and explaining the value of evidence-based practice, where clinicians base clinical actions upon the best available evidence (with a dash of expertise and service user input). With regards to palaeo/paleoradiography I am particularly hot on developing best practice for the radiographic imaging of archaeological remains. Unlike most of my archaeological imaging thus far, today's objects were burial urns - comprising of earth, pottery and bone. Whereas previously I've been able to image bones in isolation, using dedicated exposure factors, this time I had to experiment somewhat.
Dana had brought some Roman age burial urns from Cheriton, near Folkstone (UK). This was the first time I have experimented with imaging a 'soil block' type of material. It wasn't a soil block of course, but that's the best way of describing it as the bags looked like lumps of soil. Bizarrely, the urn itself had perished or disintegrated, leaving the contents of the urn. These were in plastic bags, nicely formed, but slowly falling apart.
A label for one of the urns.
Lisa Duffy, a PhD student in archaeology, adjusts the collimation for one of the urns. I'm just behind her, with a watchful assembly of undergrad archaeology students. Lisa is working alongside me to image an assemblage of Roman bones.
Before the urns are taken apart and analysed for contents, Dana wished for them to be imaged with x-rays. We were expecting bones, and potentially some metal work (coins, or votive offerings). After an excitable chat we set to work. There were a number of archaeology and radiography undergrad students loitering around, along with a token MSc Forensics student. The reason for their being with us was pure curiosity, not for any form of assessment or teaching. It was a valuable teaching session anyway, but not something I planned in advance. In actual fact we were rather hopeful of an ancient Egyptian mummified head which Dana was due to bring. Alas, for whatever reason this did not occur.
Different exposure factors - kV is the force of the x-rays, mAs are the quantity of x-rays. These images have been windowed a little (I've changed the brightness/contast), but you can see that with greater mAs the peripheral areas of the urn have been lost. Comparatively, the peripheral areas are of lower density. The urn is position 'obliquely', with the conical point to the right.
After a while we developed a system whereby we positioned the urns on the detector, took a photo with a scale, and then exposed with radiation. I decided to make use of my marker so that we could have a known point of reference when turning the image around to match the photos. I simply put the Left marker on the left of the object. We experimented with the exposure values, ending up with 102 kV and 10 mAs, giving enough power to penetrate the material and enough x-rays to demonstrate the contents sufficiently. Once we had agreed upon the exposure values (and sticking with a distance of 100cm) we re-imaged the urn using standardised views - two laterals and an inferior/superior image. In this instance, lateral simply means from the side (turning the urn 90 degrees to re-image as another lateral) and the inferior-superior meant placing the urn on its top (the flat end) and imaging it from above.
I am certain I'll create some diagrams at some stage to explain all this.
One of the urns, positioned on a digital radiography detector, supported by a sponge. My radiographic marker states the side (Left) and my initials (JE). The urn is placed on its top, with the conical tip uppermost. Because the x-rays are passing through the bottom to the top of the specimen this was termed as an inferior-superior position.
The inferior-superior x-ray of one of the urns, showing a dense structure towards the top of this image. This is most likely bone, as suggested by Dr Ellie Williams (a lecturer in archaeology).
Dana and her colleagues will subsequently take the urn apart and try to reconstruct some information about the deceased. There may be coins within the material that are of too low density to be seen on these images. In this example the use of radiography has been shown as a valuable non-destructive and non-invasive method of assessing a specimen prior to destructive analysis. The session today was invaluable to ascertain how to image specimens of high density using our digital radiographic equipment (usually reserved for living flesh and bone).
Dana, Dr Ellie, Lisa and I are due to meet next week to conduct some more imaging and discuss how we will standardise our imaging approach yet further.
Images: All x-rays were taken by the author, with accompanying photos from Dana Goodburn-Brown. With kind permission of Dana Goodburn-Brown and Canterbury Christ Church University.