X-rays are electromagnetic radiation like visible and ultraviolet light, but with a much shorter wavelength. When X-rays reach a surface, some of the X-rays are reflected or absorbed and a ‘shadow’ is cast which can be imaged with the correct equipment (Mairinger, 2004, pp 54-58).

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Due to the small size of the X-ray machine at the University of Lincoln, the charter was placed inside, folded up, and only the seal was imaged fully. The difference between the seal’s original wax and the newer brown wax added as a repair in the past is obvious in a normal photograph, but the X-ray image shows metal pins inserted to attach the newer wax; the difference in structure of the waxes is also visible, with the newer wax appearing homogenous while the original has numerous dense inclusions.

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Further information on the internal structure of the seal could be revealed with X-ray tomography, where numerous ‘slices’ of the object are imaged with X-rays, producing a 3D rendering of the object’s internal structure depicting features like bubbles and layers in the wax – these features indicate manufacturing processes (bubbles may result from water or air trapped when melting wax, layers from kneading and folding wax)  (Karch et al., 2016, pp. 26-27).