This project falls within the scope of initiatives aimed at understanding and preserving Cultural Heritage, so that it can be better passed on and preserved for future generations. When focusing on an art object, it is not only essential to study its structure, creation, history, and significance, but it is also necessary to understand its past and current material state as well as projected changes or alterations in the future. This is a continuous and complex process which requires deep interdisciplinary collaboration. In the case of historical paintings, which are heterogeneous objects, made of stacked thin layers containing both organic and inorganic ingredients that have dried together, aged and interacted within uncontrolled environments over long periods of time, one of the multiple approaches to increasing our knowledge of them is to study how macroscopic observations correlate with chemical make-up at the microscopic level. The aim of SCIMITAR was to take part in these efforts using mass spectrometry imaging, and especially Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), to investigate the microstructure of the dried paint. These chemical imaging techniques have grown in relevance in the field of heritage science over the last decades, as they are especially suited for heterogeneous systems. ToF-SIMS can for instance simultaneously localize and identify both organic and mineral components (such as pigments, binders, degradation products), and its sub-micrometer spatial resolution is very valuable to investigate painting micro-samples that consist of sub-millimeter stacked layers of dried paint that contain both organic and inorganic ingredients. While studies over the last two decades have attested to the potential of ToF-SIMS in providing information relevant for investigating painting samples, several challenges must be addressed to fully integrate ToF-SIMS imaging into the heritage research toolbox.
ToF-SIMS imaging yields multidimensional, complex datasets where much of the information is not fully understood and therefore often with a large proportion remaining unexploited, or not accessible due to technical limitations. As an example, the high energy ion source causes large biomolecules such as proteins to fragment, making it impossible to identify them intact. As a variety of protein-rich ingredients coexist and age in paintings, being able to identify them while accessing their spatial distribution at the micrometer scale would be extremely valuable. The project aims at developing methods to reduce the ambiguity of the materials identified in the heterogeneous microstructures of old paintings samples using a ToF-SIMS instrument, by addressing specific analytical limitations. Correlation between materials and their signal can be investigated using novel Tandem MS imaging capabilities and a well-documented material library from conservation institutions. Additionally, the project aims at developing alternative ways to allow targeted imaging of proteins in painting materials using ToF-SIMS, for instance thanks to its combination with immunohistochemistry relying on metal-labeled antibodies. The third aspect addressed within the aim of this project is to improve the shareability and accessibility of the technique by facilitating the data processing, by sharing databases, and by communicating the capabilities and limitation of the techniques to enable researchers from all disciplines to independently evaluate if the performance achievable using ToF-SIMS imaging can answer specific research questions relevant to a given sample.
At the end of the project, dissemination of the collected data, established protocols, and developed methodologies will advance the mass spectrometry imaging field toward achieving routine ToF-SIMS imaging of cultural heritage materials.
