The UK and mainland Europe are home to some of the world’s most diverse cultural heritage sites and historical artefacts. However, threats from the combined impact of atmospheric pollution, negligence and inappropriate restoration measures, which often results in irreversible damage, pose a major challenge for heritage scientists. In a proactive response, the ARHC/EPSRC Science and Heritage Program was launched to ensure that knowledge and innovation in UK cultural heritage research is strengthened by developing new capacity within the research community to support interdisciplinary scientific research to tackle complex archaeological challenges that face the 21st century .
The application of non-destructive synchrotron techniques to probe changes in the surface and structural properties of materials under reactive environments will prove pivotal to improving our ability to conserve historical artefacts . Such capabilities are central to aiding our understanding of the interactions between the surfaces of historical artefacts and their surrounding atmosphere, and in turn identifying processes which lead to weathering or decay phenomena observed in many conservation projects. The brightness of modern synchrotron facilities allow improved analytical sensitivity for time-resolved measurements during exposure of historical artefacts to reactive environments, while also permitting simultaneous multi-technique characterisations (e.g. Raman, XRF and XAS). Since the closure of the SRS, only the LUCIA beamline at Soleil is capable of measuring XAS on light elements (e.g. Na, Mg Al K-edges) . However, LUCIA is a dedicated μ-focus beamline and cannot analyse first row elements or permit time resolved environmental studies, thus VERSOX will fill an important gap in the armoury of spectroscopic techniques for heritage science.
Heritage conservation requires an understanding of the kinetics of decay processes, and how to mitigate and manage deterioration of artefacts by adopting the most appropriate preservation policies. Materials conservation not only addresses our past, but also our future with ageing behaviour of modern day materials (e.g. photographs, composites and polymers) selected for archiving also presenting a challenge. Climate change has a significant influence on both indoor and outdoor environmental conditions; understanding the interaction of variable microclimates with materials is thus key to deciding preservation policies and practices. Such climates can range from aggressive environments as in the case of atmospheric pollutants with surfaces of masonry, sculptures or ancient glass on buildings and monuments, to more subtle effects of humidity on artwork, textiles, parchment and photographs. There are only two soft x-ray beamlines in operation currently capable of performing the ambient/high-pressure measurements offered by VERSOX, both are heavily over-subscribed by the international community and lacking the proposed complementary high-throughput XAS facility on the second end-station. The capabilities of the VERSOX beamline will be invaluable for probing the transformations involved in all these projects, and it is anticipated that the range of applications will continue to expand as the new heritage community matures.
Hydration and relative humidity has a significant effect on the molecular and mesoscopic structure of parchment, with the surface-ink interface often undergoing degradation as a result of environmental damage [4,5]. Analysis of such ink-surface interactions on parchment using micro-focused X-ray spectroscopies to probe the upper few microns of the surface where writing is found will allow local changes at the surface of parchment to be probed shedding light on the mechanism of this important degradation process . Given this information, new protocols for archive record maintenance, storage and novel cleaning techniques can be established.
A pressing current challenge in conservation, archaeology, anthropology and art history is the fully-integrated study and management of artefacts made from animal tissues such as ivory. These materials are inherently complex and the authenticity and origin of the source of the material is often problematic and requires a non-destructive approach to more accurately catalogue the materials according to their elemental composition. It is essential that our ability to determine the origins, authenticity and date of ivory objects and working residues is substantially enhanced. μ-XRF and XAS analysis will a powerful method to map the elemental compositions and local structures of ivory-based materials.
Metallic and wooden artefacts
Many metallic artefacts are found to decay post-excavation, which is related to the presence of Chlorine. The processes by which corrosion phases form, and later evolve, strongly influence the conservation and restoration of these metal artefacts. The microscale variations of iron and chlorine speciation along the depth of the corrosion crust could be determined using μ-XAS. Furthermore environmental XPS would allow a greater understanding of the surface chemistry and dynamics of the initial stages of the decay process. Distribution of metals in composite materials can be probed by μ-XRF, μ-XAS. e.g. swords comprised of Fe, As, Ni composites, or Fe and Cu in Egyptian bronzes where changes in oxidation state can be observed by deterioration.
Synchrotron studies at also revealed the origins of decay in timber frame of the salvaged Tudor warship The Mary Rose. Sulphuric acid formation, identified deep within the timbers, was observed to react with the timber surface leading to its decay. Unfortunately existing preservation methods are unable to prevent the acid formation, however, having identified the problem, new preservation methods can be sought to prevent the formation of sulphuric acid and retard the decay within the timbers and so save the historic remains of this ship.
Masonry and sculptures
An understanding of how to combat pollution induced weathering of masonry from historic buildings and sculptures,such as York Minster  requires access to XAS facilities capable of measuring light elements (e.g. C, S, Mg, Al, Ca) and is ideally suited for the soft x-ray specification of the proposed VERSOX beamline. Imaging of light elements will prove valuable for mapping local regions of decay and elemental distribution within masonry samples and identifying the local structure of amorphous salts. XPS will permit the interaction of atmospheric gases with historic masonry to be examined to aid our understanding of the influence of hydration (relative humidity) upon salt formation. In addition the effect of organic acids with surfaces of building materials can also be investigated to assess the effect of modern day pollutants on historic buildings.
The effect of weathering on medieval stained glasses can result in changes in glass colour, as well as the formation of surface weathered phases. The combination of μXRF and μXAS information contributes to our understanding of the way chemical phases react as a function of the long-term weathering, but also to the conservation of these stained glasses [8,9].
An improved understanding of the effects of micro- and macro-environmental conditions on the degradation of colour photographic media is essential for the preservation and management of colour photograph collections for future generations [10,11]. Artificial ageing methods are being employed to follow the aging of colour photographs under different environments. Analysis of the resulting changes requires by an array of spectroscopic techniques to map out the changes as the photographic dyes degrade. By constructing a model of the environmental effects on the stability of colour photographs using such non-invasive measurements will allow the life expectancy of colour photographs from The National Archives to be estimated.
Polymers and plastics
Heat-set tissues were once applied to paper as a remedial conservation treatment. The nature of the substrate and adhesive, combined with the application of heat, can be detrimental to the long-term stability of laminated documents. The issues surrounding the identification and deterioration of synthetic polymers are of growing concern within the heritage sector. They pose significant stabilisation problems because of the processing methods, additives and treatments used. The routes of degradation are often complex, requiring an intimate knowledge of the interfacial chemistry between the paper and laminate in order to develop conservation and preservation protocols.