A combined approach to the vibrational characterization of medieval paints on parchment: Handheld Raman spectroscopy and micro-SORS

A careful analytical study of the paint materials used in medieval illuminated manuscripts and their respective formulations is critical to their preservation. Due to their high value and fragile nature, access to these objects is often limited. Therefore, the development of ad-hoc methodologies allowing researchers to collect data in the least invasive way possible is an essential task in conservation science. This article shows the potential of a combined approach that complements handheld Raman spectroscopy with micro-SORS for the characterization of medieval paints. This methodology was tested on a reference collection of mock-up samples prepared as pure, mixture, and layered paints on parchment, based on historical information regarding paint formulations from Iberian scriptoria. Conventional Raman analysis, carried out by means of two handheld spectrometers, was found particularly effective for materials identification in pure paints and multi-component formulations of increasing complexity. Complementing this data, micro-SORS proved decisive in differentiating between mixture and layered paints in most mock-ups examined, yielding detailed information about the stratigraphy of reference samples produced through the overlaying of different paints. This combined methodology may be helpful to researchers who would like to approach the vibrational characterization of paints applied onto fragile artifacts and supports in a totally non-invasive manner.