Non-Destructive High-Resolution X-ray Diffraction for Cultural Heritage

Many different analytical techniques are commonly applied in the scientific analysis of heritage objects in order to elucidate their material properties. Each technique has advantages and disadvantages in terms of the type of information returned, complexity and expense, sample preparation requirements and applicability to different types of material objects. While X-ray fluorescence (XRF) is very useful in providing elemental information, and techniques such as Fourier-transform infrared spectroscopy and Raman spectroscopy can yield phase information, only X-ray diffraction (XRD) allows the definitive and unambiguous identification of crystallographic phases. Despite this, the use of XRD in archaeometry has been relatively sporadic and of utility only in niche areas, largely because of sample preparation requirements. This project aims to bring exciting advances in non-destructive XRD techniques to the archaeometric analysis of cultural heritage and archaeological artefacts. The innovative XRD methods developed by the applicants enable high resolution XRD analysis of objects with no sample preparation requirement at all. While twenty years ago sampling of artefacts was considered standard practice, the growth of non-destructive techniques such as handheld XRF have made curators at museums and other collections very much less willing to allow invasive procedures. Maintaining the physical integrity of heritage artefacts is now considered to be of paramount importance.

There are certain classes of heritage objects for which destructive sampling is currently the only realistic approach to determining provenance. Stone artefacts are a primary example. Many stone objects in Western Museums are from the art market and doubts have been expressed about the authenticity of many. The most effective method of provenancing stone artefacts is the detailed characterisation of the mineralogical composition in order to identify the geological source, but destructive sampling is nearly always currently required for this purpose. A second major application area is the identification of pigments in fine art paintings and on painted objects such as mummy portraits and Indian miniatures. Although Raman spectroscopy can successfully identify a significant proportion of pigments, there remain an important number for which the method is ineffective. Pigments have unique diffraction pattern fingerprints and XRD studies can provide the critical information for essentially all pigments. The study of stone artefacts and of paintings and painted artefacts will form a major focus of the proposed project.

Currently, this innovative XRD technique requires synchrotron facilities for implementation. The applicants will demonstrate the method using cutting-edge high-resolution X-ray detectors (superconducting transition-edge sensor arrays) at the National Institute of Standards and Technology in the US in proof-of-principle experiments. This work will support the eventual transition of the technique away from synchrotrons and into the laboratory and museum. An additional aim is to investigate the archaeometric capability of a prototype handheld XRD instrument, based on the same underlying technique but having much lower resolution. Previous work with this prototype device strongly suggests that the analysis of metallic heritage objects is an especially promising area.

The avoidance of the need to extract samples from high-value and rare objects is a highly-significant advantage and is applicable in other research areas. These include palaeontology and the study of meteorites and planetary materials brought to Earth by sample-return missions.

The uniqueness of this research lies in the ability to perform highly accurate crystallographic analysis without the need for any preparation of the sample, even for markedly non-planar and textured objects. This capability is greatly enabling, opening up new opportunities for detailed investigations of the crystallographic material properties of a wide range of objects.

Museums and their curators will benefit from access to the new knowledge generated during the project and, in the longer term, through the establishment of highly capable XRD analytical facilities situated within larger museums with more extensive collections. The new knowledge will lead to improved explanatory and contextual information displays about collections. Access to up-to-date research will support museums as evolving entities within communities, contributing to individual and societal well-being and supporting economic tourism and so benefiting the wider public.

There is potential for further significant economic impact through verification of the authenticity of artworks, directly benefiting auction houses and insurance companies. For example, the identification of pigments can place strong constraints on the date and location of manufacture and this information is extremely valuable for high-worth artworks. Buyers of art, including museums, will benefit through assurance of the veracity of their purchases. The UK is home to several internationally-leading auction houses (Christies, Sothebys, Bonhams) and the proposed research will support these leading roles, ultimately to the benefit of the UK economy.

The PDRA employed on the project will receive first-class cross-disciplinary scientific training at the Universities of Leicester and Cranfield. S/he will develop key employability skills, including communication, presentation and organisational skills and team working. Summer students will also be employed on the project and will have the opportunity to gain an invaluable insight into cutting-edge research, guiding their decisions about future careers.