Spectroscopic characterizations of Ferrogallic Inks and related pigments with interest in Cultural Heritage

Abstract

Iron gall ink (IGI) was the most widely used writing material until the early 20th century. They are probably the most broadly used writing and occasionally drawing tools throughout our history. Its extensive use at the world level, has allowed the conservation and transmission of different recipes for its manufacture. Despite the immense diversity of recipes available from very different cultures and periods, all of them present a series of constant components in their composition. Recurrently, there can be find vegetable polyphenolic substances and mineral sulfates agglutinated by resins from trees in recipes. The investigation of inks is crucial in many aspects. In particular, it is of a great importance in the study of historical manuscripts with many applications in cultural heritage. However, to analyze such complex systems, it is important both to develop an appropriate analytical method as well as to identify and characterize their individual components. That is why the purpose of our research project is to perform a structural analysis of IGIs, especially of the complex formation of gallic acid and other polyphenols with a similar structure, such as pyrogallol, syringic acid, tannic acid, with iron and copper ions. In this doctoral thesis, we mainly present results obtained by using different optical spectroscopy techniques (UV-vis absorption, IR, Raman and SERS) to study the reaction mechanisms of polyphenolic compounds and their iron and copper complexes. The structure of the actual colorant in IGIs is still a matter of controversy, therefore, this work could represent an important and interesting contribution to the description and understanding of the IGIs chemical structure and composition. In the final part of this thesis, Raman spectroscopy was applied and optimized for the in-situ and non-destructive analysis of historical manuscripts. An analysis of the aging process undergone by the manuscripts was done on the basis of the vibrational marker bands deduced from the study of the previous molecular models and the SERS results