NextGenHS – Next generation analytical tools for heritage science

In heritage science, analytical tools play a key enabling role. Understanding the extreme compositional and structural complexity of historic objects, specifically those made of biomaterials, is similarly difficult to that of live organisms, whereas sampling is also often ethically questionable. Another similarity is that in order to interpret the results, an intense interdisciplinary effort is needed.

NextGenHS focuses on the development of new analytical methods and techniques for historic biomaterials, for the purpose of their better interpretation, management and conservation. This requires interdisciplinary collaboration of analytical and material scientists, as scientific interpretation of results cannot be achieved without a deep understanding of structure and decay processes. For this reason, the proposal is submitted in the field of analytical chemistry (primary field), supported by UL FKKT, UM and KI, and biotechnical sciences (secondary field), supported by UL BF, ZAG and ZVKDS. The impact is in the humanities, represented by UL FF and NUK (Partner description cf. p. 13). NextGenHS supports the delivery of the SDG 11 “Sustainable cities and communities”, specifically Target 11.4 “Strengthen efforts to protect and safeguard the world’s cultural and natural heritage”. The 2018 Angewandte Chemie (57, 7260-7261) Special Issue reviewed the state-of-the-art in the field. In his Editorial, M. Strlič calls for a “significant research and technical effort […] to develop the monitoring tools and data analysis expertise that is required [to understand, interpret, and manage heritage]”.

As an analytical challenge, heritage biomaterials represent complexity on diverse scales:

• Compositional complexity. The vast majority of heritage biomaterials are either of natural origin (e.g. wood, bone) or represent processed natural materials (e.g. parchment, paper). As such, they reflect the natural composition of the tissues from which they have been made.
• Structural complexity. Many heritage objects are composite structures, either quasi-2D, such as layered decorated surfaces (e.g. paintings), or materials with a diverse 3D distribution of chemical and mechanical properties, e.g. wood or bone.
• Long periods of degradation in unknown conditions may have locally altered the composition and structure significantly and introduced further heterogeneity, with the analytical understanding of the environments representing a further challenge.

This extreme complexity can be a source of information enabling the understanding of heritage objects (e.g. compositional differences in teeth growth rings that can indicate changes in diet), but it can also be the cause of degradation (e.g. due to mechanical/moisture-induced stresses within a material leading to internal cracking). Characterisation of the microenvironments surrounding objects with a sufficient temporal resolution could inform both conservation and identification of materials (e.g. through detection of volatile organic compounds). The ability to analytically visualise material heterogeneity thus directly informs interpretation as well as conservation of heritage objects in museum, gallery, library and archival collections. NextGenHS addresses some of the most frequent and unresolved analytical challenges in heritage science.

Cutting-edge development of analytical methodologies and techniques in the field of heritage science is enabled by the European Research Infrastructure for Heritage Science (E-RIHS). All of the project partners are members of the Slovenian node, E-RIHS.si, and thus ideally placed to offer access to the novel facilities immediately after project completion, ensuring global impact.

Slovenian heritage scientists have shown excellent global leadership through their role in the development of E-RIHS: in 2015, the E-RIHS consortium submitted a proposal to ESFRI – the European Strategy Forum for Research Infrastructures, to support the inclusion of the E-RIHS infrastructure in its roadmap, which was achieved in 2016. Immediately following that, the EU funded the Preparatory Phase project (E-RIHS PP, 2017-2020), with Slovenian partnership, in which the legal, financial, organisational and scientific frameworks for the developing infrastructure have been developed, with the aim to submit ERIC Step 1 documentation, which took place in 2021. The EU Commission positively evaluated it, and the consortium prepared Step 2 documentation with the aim to transition into implementation in 2023. This is supported by a further EU grant, the Implementation Phase (E-RIHS IP, 2022-2024), also with Slovenian partnership.

Therefore, to enable E-RIHS.SI partners to push the envelope and develop cutting edge analytical facilities that will guarantee its leading role for the next decade, funding through this proposal is essential. We will develop four new analytical facilities (LABs), the justification for which has been approved through the E-RIHS Preparatory Phase project and its gap analysis document: Services for New Communities of Users, in 2020.

The project goals and planned research are described in four challenges:

Challenge 1: E-RIHS.SI Surface Analysis LAB

Although a great variety of analytical methods are used for surface analysis, with excellent spatial resolution at nanometer scale, few enable chemical characterisation to the level of organic or inorganic compositional analysis and/or elemental oxidation state analysis. Synchrotron methods, particularly X-ray absorption spectroscopy (XAS), have been successfully used to quantify and visualise oxidation states in heritage biomaterials, from iron-gall inks on paper and parchment to waterlogged wood corroded by iron, soft-rot decay and acidity, however, for lighter elements and in easily accessible research laboratory environments, X-ray photoelectron spectroscopy (XPS) is more suitable and provides complementary information to XAS. In addition, Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) can provide chemical compositional information, some of which can partly be deduced using spectroscopic methods (synchrotron-based or not). This challenge will be supported by an array of well-established analytical methods, for which there is evidence of research excellence in Slovenia, such as Laser Ablation ICP/MS, Raman and FTIR spectroscopy and imaging. 

Challenge 2: E-RIHS.SI Quantitative Chemical Imaging LAB

Hyperspectral imaging in the interval 400-2500 nm is an established technique of analysis and visualisation of heritage and art surfaces. In the VNIR range (400-1000 nm), whether in reflection or fluorescence mode, it is used to map (with spatial resolution typically 10-30 mm) the distribution of pigments, dyes, inks, and other surface layers that are optically distinct from the background, such as surface alterations and restorations. The resulting hypercube data requires data analysis techniques that often involve supervised and non-supervised multivariate data analysis in order to identify pixels with similar spectra, which indicates similar composition. Such clustering methods are typically enabled by either proprietary HSI software, or ENVI, an industry standard generally applicable to HSI data.

On the other hand, the spectral range 1500-2500 nm has features consisting of overtone and combination vibrations that will be used for quantitative chemical imaging in this project, e.g. using multivariate calibration. In a first, this approach was introduced to heritage science by our group in 2011, however, due to complex calibration requiring extensive sets of independently characterised reference samples, it has not been widely applied yet. To introduce it to a wide audience, we will determine the analytical performance of diverse methods developed for historic wood, parchment and paper.

Challenge 3: E-RIHS.si 4D imaging LAB

X-ray computed tomography (CT) is the technique of choice for visualization of internal structure of diverse organic materials, including wood and bone/teeth. It enables full-volume nondestructive testing of entire objects with diverse spatial resolutions:  μCT typically as low as 0.5  μm. The 3D image reflects differences in X-ray absorption per voxel, which reveals the internal structure of an object non-destructively. This is of interest in object interpretation, e.g. by revealing methods of manufacture, and conservation, e.g. revealing the presence of internal faults. μCT DVC is a state-of-the-art approach in many fields of material science, e.g. biomaterials, however, it is virtually unapplied in heritage science. We will demonstrate its applicability to diverse problems related to the behaviour of wood, bone, parchment under loads, e.g. during mechano-sorptive load. To evaluate analytical performance, we will use traditional methods of static and dynamic mechanical testing and material characterization. 

Challenge 4: E-RIHS.si Sensor LAB

Indoor heritage environments have a complex composition as they are influenced by outdoor-generated pollutants penetrating through the building envelope, by visitors, and by emissions from indoor furnishings as well as from collection materials. Heritage microenvironments are thus both a hazard and a source of information about the materials. In another world first, this project group demonstrated that quantitative analysis of VOCs emitted from historic paper can be used to infer not just the composition of such paper but also its stability. Increased emissions of VOC can be the first sign of fungal infestation. However, monitoring of complex pollutant mixtures is a difficult analytical problem that has not been adequately resolved in heritage environments. Despite the availability of GC-MS, the requirement to sample introduces significant delays into heritage management. Sensor arrays offer the possibility for rapid detection and quantification of complex mixtures; however, their calibration requires diverse machine learning approaches and the availability of calibrated environmental data obtained using GC-MS. We will develop sensor arrays for simultaneous quantitative monitoring of complex gas-phase mixtures of indoor heritage environments. Such sensor arrays will complement the already available sensors for traffic generated pollutants, frequently deployed in heritage institutions.

Partnership:

The project J7-50226 is funded by ARIS (Slovenian Research and Innovation Agency) and involves:

• University of Ljubljana, Faculty of Chemistry and Chemical Technology, Heritage Science Laboratory Ljubljana (Irena Kralj Cigić, Matija Strlič)
• University of Ljubljana, Biotechnical Faculty, The Department of Wood Science and Technology (Miha Humar)
• University of Ljubljana, Faculty of Arts, The Department of Archaeology (Matija Črešnar)
• National Institute of Chemistry (KI), Department of Analytical Chemistry Chemical (Samo Hočevar)
• The National and University Library (NUK) (Jasna Malešič)
• University of Maribor, Faculty of Chemistry and Chemical Technology, The Laboratory for Analytical Chemistry and Industrial Analysis (Matjaž Finšgar)
• Slovenian Building and Civil Engineering Institute (ZAG) (Lidija Korat)
• Institute for the Protection of Cultural Heritage of Slovenia (ZVKDS) (Polonca Ropret)