The Inter-instrumental Comparability of Semi-quantitative ED-XRF Analyses of Iron Gall Inks

This paper was presented at the YRA Workshop 2025 in Budapest.

A systematic chemical investigation of ancient and medieval inks from known socio-geographic contexts could enable a non-invasive, indirect dating of manuscripts. This prospect led to the development of a standardised protocol for the in-situ analysis of inks in historical manuscripts, incorporating energy dispersive X-ray fluorescence (ED-XRF) spectroscopy. Due to the heterogeneous, thin-layered ink-on-support matrix, ED-XRF analyses of inks are limited to semi-quantitative results. Given the wide variety of configurations in ED-XRF spectrometers, concerns persist regarding the comparability of data generated by different devices. This study addresses these concerns by analysing mock-ups with known ink compositions and a historical manuscript sample using five ED-XRF spectrometers. The results reveal significant discrepancies in relative elemental intensities across spectrometers, linked to factors as the anode material, X-ray optics, incident angle, and acquisition mode. These findings underscore the need for detailed metadata, robust calibration routines, and the use of standard reference materials in the ED-XRF analysis of writing materials. The study calls for greater dialogue among heritage scientists to refine analytical protocols for ink analysis, in order to support reproducible and interoperable data across laboratories and ultimately pave the way for a reliable ink database.

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