Phenolic Composition of Historical Iron-Gall Inks: A Comparative Study of Galician and Catalan Galls by HPLC-MS

Abstract This study analysed the phenolic composition of iron-gall inks made from galls collected from Galicia and Catalonia, using High Performance Liquid Chromatography coupled with Mass Spectrometry (HPLC-MS) to identify and compare the relative concentrations of gallic and ellagic acids. Three historical recipes were reproduced, and the inks were subjected to two years of natural ageing. Significant differences in the phenolic profiles were observed, influenced by the geographic origin of the galls, the extraction method, and the solvent used. Inks made with Catalan galls showed higher relative concentrations of soluble phenolic acids. Gallic acid is primarily released through the hydrolysis of gallotannins, while ellagic acid can form through oxidative processes involving gallic acid. A higher relative amount of ellagic acid in certain formulations therefore suggests a more advanced oxidation process. These findings highlight the influence of regional ingredients and preparation methods on the chemical profile of iron-gall inks.