Characterisation and stability of inks on paper

It is impossible to imagine present world cultural heritage without the discovery of inks. Their use for writing, drawing and painting goes back for many centuries. The oldest and probably best known inks are carbon based, but many others, such as iron gall, logwood and sepia bear equal historical importance. In heritage science research, they often prove extremely challenging for characterisation due to their heterogeneity, presence in mixtures, limited sampling, aging effects etc. Lack of proper analytical methodology and optimised analytical tools for identification of inks often leads to over-simplifications of analytical results and technological misinterpretations. For example, in the case of iron based logwood inks, measurements are often interpreted as iron gall inks, while sepia or carbon based inks can be equally incorrectly concluded only on the basis of absence of iron. Incorrect interpretations do not only influence the art historical and technical knowledge; they can provoke harmful effects on heritage preservation, and conservation treatments, especially in the case of chemical stabilization, which is very often used in the case of iron gall inks. Furthermore, there is considerable lack of knowledge about the environmental influences on stability of inks on paper. Currently, museums worldwide employ many versatile illumination systems. Introduction of new ones (e.g white light emitting diodes) require in-depth studies of their photochemical degradation. The overall objective of the proposed project is to design analytical methodology to properly characterise and classify inks (focusing on iron gall, logwood, sepia and carbon based inks) present on selected works on paper from Slovenian National Collections (National and University Library, Ljubljana and National Gallery, Ljubljana). Due to the priceless value of the investigated objects, advancements in analytical methods for minimally invasive, non-invasive (without sampling) and on-site measurements will be proposed and optimisation of Surface Enhanced Raman Spectroscopy (SERS) procedure developed. SERS will be complemented with other techniques offering elemental/molecular composition (such as X-ray fluorescence, infrared spectroscopy, electron paramagnetic resonance), addressing several aspects such as traces detection, coordination of transition metal centres, and interaction with the paper, and state of degradation. The spectral knowledge databases of the mock-ups will serve as a basis for the sound ink characterisation and classification of the National Collections. Experimental research will be combined with theoretical research (modelling) which will serve as a basis for recommendation (guidelines) for the preventive conservation of such works of art. To achieve overarching goal (WP3), several specific objectives will have to be met: OBJECTIVE 1: To optimise SERS procedure using HPC-based SERS substrate for minimally invasive or non-invasive SERS characterisation of inks with the possibility of the on-site characterisation (WP2). OBJECTIVE 2: To develop analytical methodology for sound ink characterisation (WP2). OBJECTIVE 3: To determine the effect of irradiation wavelength and intensity on the degradation and stability of inks and to populate a predictive model with the developed response functions using experimental measurements, creating an all-encompassing degradation model (WP4). OBJECTIVE 4: To prepare the guidelines for curators for the light source selection (WP4). The proposed project will bring several advancements beyond the state of the art and impact areas of science in the development in analytical chemistry and heritage science, new knowledge databases, interdisciplinary research in Humanities, progress within European Research Infrastructure for Heritage Science (E-RIHS).