The Royal Armouries has always emphasised the importance of non-destructive scientific investigation of its collection and chamberless X-ray fluorescence (XRF) analysis provides a means of finding the chemical composition of artefacts (or parts of artefacts) without removing samples.
The instrument in the museum has provided a unique facility within a United Kingdom museum which has benefited the museum in many ways.
X-rays are generated using an X-ray tube and focussed onto the surface to be analysed. At its simplest, the technique examines the signal given off by an object which has had X-rays directed at it. This signal shows which chemical elements are present, what quantity and in detail.
The technique is capable of great accuracy with clean, flat, homogenous samples that can be compared with standards of similar, known, composition.
This is rarely the case when looking at historic or archaeological artefacts however, particularly where the surfaces of the object are analysed without sample removal or, where surface cleaning is unacceptable. Such surfaces will have undergone changes in composition due to corrosion and the original material may have been far from homogenous. The technique must be used with care and the resulting data must not be over-interpreted.
Without the limitation of a sample chamber, objects of any size can be investigated without the need for sample removal. Chamberless XRF does however have the disadvantage that it cannot detect light elements (below titanium in the periodic table), because the secondary X-rays from these elements are absorbed by the air in the gap between artefact and detector.
Uses of X-ray fluorescence
- At the most immediate level, analysis provides data on the materials of manufacture, ensuring that the museum’s records of the object are accurate.
- The instrument is a key tool for the technological investigation of objects and of the history of technology in general, by helping to build up our understanding of the historic use of materials and processes.
- Where the materials identified are not consistent with those available at the date of manufacture, this may indicate either restoration or fraudulent reproduction: Case study.
- Through investigation of composition, it is often possible to suggest the original appearance of an object that has undergone visual change, due to corrosion, wear or deliberate alteration: Case study.
- The identification of materials and the presence of surface coatings, often where they are no longer visible, allows best conservation practice to be followed: Case study.
- By enabling the detection of certain hazardous materials, such as mercury, cadmium and arsenic, it contributes to the health and safety of museum staff and visitors.
- As a unique facility it has enabled high profile “discoveries”, providing publicity and academic kudos for the museum: Case study.