Iron-gall inks have been described as complexes of iron ions with gallic or tannic acids, available in gall extracts. To assess this working hypothesis, we have prepared medieval inks using ingredients and methods appropriate to the fifteenth to seventeenth centuries. The five historical inks studied were selected based upon research into Iberian written sources of medieval techniques. Results are supported by comparison with iron complexes with a well-characterized phenol counterpart: gallic, ellagic, and tannic acids as well as digalloyl and pentagalloyl glucose; as either precipitates or prepared as inks by adding gum arabic. Raman and infrared spectroscopies show that medieval writing inks could not have been represented solely by iron complexes with gallic acid. Overall, writing inks display the infrared signature of gallotannins, indicating that complexes of Fe 3+-polygalloyl esters of glucose are also formed. Our results also show that the commercial tannic acid solution is far more complex than the gall extracts, and cannot be used to represent a gall extract (as described in historic written sources). High-performance liquid chromatographyelectrospray ionisation, HPLC-ESI-MS, reveals that the concentration of gallic acid varies in the gall extracts, depending on the extraction method and ink recipe. Importantly, in certain recipes, gallic acid is found as a minor compound, when compared with the galloyl esters of glucose.

One contribution of 14 to a theme issue 'Raman spectroscopy in art and archaeology'.

Abstract Illuminated manuscripts are the most abundant and well-preserved surviving medieval cultural artefacts. Created to contain sacred texts, their visual structure allows the reader to identify divisions and delight in their beautiful ornamentation and iconography. Western European manuscripts were written on parchment, which was the main writing support in the Middle Ages prior to the rise of paper production in the fourteenth–fifteenth centuries. Highly functional, durable animal skins were also used in medieval bookbinding (covers) and have been crucial in the preservation of the illuminations. These illuminations make wonderful use of form and colour. This chapter focuses on recent advances in the molecular characterization of these colours, used in medieval manuscripts produced by Western Europeans, and the challenges inherent in analysing materials that are intrinsically heterogeneous. We then discuss how molecular characterization may reveal conservation conditions and extend our analysis to parchment and iron gall inks. Finally, we address the challenges and possibilities for this flourishing field of research. In short, we show in this chapter how analytical methods are used: – To understand how medieval illumination colours were made and what palette defines them; – To predict original colours and to understand why certain colours have remained in excellent condition, preserving both adherence and luminosity, while others have changed over the centuries; – To assess deterioration (paints, parchment, writing inks) with the goal of determining what potential restoration measures could be taken, after careful consideration.