It's all About..... X-Rays

National Science and Engineering week gave us an opportunity to look at some of the more unusual topics in archaeology, and one that has always been a mystery to me is X-radiography. We’ve all heard of X-rays – most people have had some part of them X-rayed for medical reasons – but it turns out that they are also a really helpful analytical technique for archaeologists!

Zosia at the X-ray table

X-radiography is a form of electromagnetic radiation that allows us to create images showing features and details invisible to the naked eye. It is important to X-ray metal objects to create visual record of how an artefact was made, as well as its shape and condition. X-rays can also help with identification if an artefact is hidden by layers of corrosion or concretion, and are an excellent means of scientific examination without affecting or destroying archaeological finds in any way.

For these reasons, artefacts are often X-rayed as part of the conservation process. The examples used for the handling table are all from the excavation of the Thermae Spa in Bath city centre, and were chosen because the archive contained copies of their X-rays.

X-ray of a Roman coin from the SPA98 excavations

In general almost all metal objects should be X-rayed, although it is less effective on very large examples or lead alloys. It is a useful technique because it can reveal small implements trapped within corrosion, and can often expose identifying marks on coins that have lost their surface detail. Fragile or complex finds tend to be lifted in a block of soil, and X-rayed to view and pinpoint the contents for more careful excavation in a laboratory. For example, X-raying a soil block containing a coin hoard could provide information about how it was deposited, as the image would reveal groupings or layers.

Decorative surface details such as inlay or enamel can also be seen through X-ray, and non-ferrous coatings become visible due to the difference in density between the metals.

The English Heritage guidelines on the X-radiography of archaeological metalwork (http://www.helm.org.uk/upload/pdf/X_Radiography.pdf?1331775979  ) has a number of beautiful examples that show exactly how valuable X-raying metal artefacts can be, including images of inlay details and coin identification. I really recommend browsing through it, even if it is just to marvel at the lovely pictures!

Zosia - Collections Intern