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Kent Archaeological Review extract

Science in Archaeology --
The Use of X-rays in Archaeology (continued).
by Dr Tony Cox.

In contrast to the short wavelength X-rays the penetration of the long wave length rays is small, and they are absorbed after only travelling a few inches in air. This precludes their general use in radiography, and their particular application is for non-destructive chemical analysis, known as x-ray fluorescent analysis.

When these x-rays strike a material new x-rays are generated, with wave lengths characteristic of the parent elements. Since the x-ray wave length peculiar to each element is known and tabulated, it is only a matter of comparing the unknown pattern from the find with standard known patterns, to be able to tell what elements are present.

To carry out the analysis the find is set up in the x-ray generator so that the x-rays produced when the primary x-ray beam strikes the object are recorded on photographic film. A typical film shows, the dark lines in positions unique to the various elements. The analysis obtained is only for the surface and any encrusted foreign matter must be removed to ensure a reliable result. Normally the analysis is qualitative (tells you what is there, rather than how much), but quantitative analyses are possible but involve preparation of standards which may only be justified if a series of similar analyses is contemplated. Fluorescent analysis has been particularly useful for studying the composition of glazes on pottery, while in the general study of the Piltdown remains the technique revealed that the surface of the bones was stained with a chrome containing compound.

X-rays can be used for identifying compounds, although this necessitates the preparation of a powder of the "find" material and is destructive. Nevertheless, the information gained from metal working residues, pottery glazes, and ceramics can indicate the trade and communications extant during the period of manufacture.

Recent developments in the x-ray field have seen the introduction of the electron probe microanalyser. In this instrument a finely focussed beam of electrons is directed onto the solid sample, and the x-rays leaving the surface are then collected and a pictorial representation of the composition obtained. Unfortunately, as far as archaeologists are concerned the instrument's application is limited to comparatively small finds of the order of one centimetre cubed, but no doubt larger samples will be accommodated as development proceeds.

All these scientific instruments provide further insight into the peoples associated with the finds, and one must hope that this latent information in the materials will be uncovered, and woven into the fabric of Kentish History.

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