Shedding light on dyes interactions: recipe and environment - dependent effects in ink formulations

This thesis investigates the degradation mechanisms of 19th- and early 20th-century writing inks, focusing on natural and synthetic organic dyes. While prior studies have relied mostly on non-destructive techniques and emphasized paper degradation, this work addresses the lack of analytical protocols for identifying the molecular profiles and ageing products of inks. By combining simulated ageing with advanced liquid chromatography, colorimetry, and Raman spectroscopy, this research models the complex interactions between dyes, formulation parameters (e.g., inorganic cations, interim dyes, organic acids), and environmental factors (e.g., relative humidity, volatile organic aldehydes, light). Reference inks based on historical recipes and artistic collections were in-depth investigated using tailored micro-destructive HPLC-DAD-ESI-Q-ToF methods, optimised during the thesis for achieving high sensitivity, high selectivity, and low sample consumption. The findings reveal key degradation pathways and molecular markers for various dyes, including tannins, logwood, and early synthetic dyes. These findings contribute to the development of more effective conservation strategies for historically significant manuscripts and artworks.