Elemental imaging approach to comparative analysis of historical inks. Proof of concept based on non-invasive examinations of the Chopin manuscript as a case study

This work presents an indirect method of investigating the elemental diversity of historical inks. The manuscript of Fryderyk Chopin's Impromptu in A flat major, Op. 29 was examined as an example of the proposed approach for testing documents containing different inks. Preliminary in situ X-ray fluorescence (XRF) measurements carried out it the museum storage room provided qualitative reference data for the object. Then, selected areas on the item were examined with indicator papers soaked in 4,7-diphenyl-1,10-phenanthroline (Bphen). The reaction with the ligand enabled the immediate colorimetric detection of Fe(II) in the form of magenta Fe(Bphen)3 complex. The overall condition of the manuscript with regard to the risk of ink corrosion was assessed in this way. More chemical information were obtained by the proposed elemental imaging-based approach to evaluate chemical heterogeneity of the used indicator paper samples using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The recorded data were visualised in the form of elemental distribution maps. The Fe enriched areas indicated Regions of Interest (ROIs) to approximate composition of the inks from the manuscript. All calculations were done solely for the data mathematically singled out from these areas. The varying proportions of AI, Mn, Co and Cu relative to Fe correlated with the ROIs of the composer's handwriting, editor's notes and stave lines, demonstrating the applicability of the proposed approach for comparative studies