New insights into iron-gall inks through the use of historically accurate reconstructions

Abstract

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.

Black Egyptian inks in Late Antiquity: new insights on their manufacture and use

“…Alternatively, it is plausible that at the very beginning of the existence of iron-gall inks, the scarce knowledge regarding their chemical structure resulted in darkish inks rather than black ones, thus carbon may have been used to blacken the mixture. A recent study seems to corroborate this idea, demonstrating that, in contrary to what Robert Fuchs asserts in his definition of 'imperfect inks' (Fuchs 2003), not only gallic acid but also other polyphenols commonly contained in tannins can form darkish complexes with Fe 2+ , but the complex iron gallate remains the blackest (Díaz Hidalgo et al 2018). This raises another question: could it be that the ink on Montserrat, Roca Puig, Inv.…”

“…As discussed, recent experiments proved that the complexity of the inks containing vegetal matter and metallic salts can hardly be described using the term iron-gall ink in a 'traditional' way, i.e. considering only the complex iron-gallic acid as responsible for the ink's properties (Díaz Hidalgo et al 2018). In addition, the recipes collected in the works of Colini 6 and Zerdoun show the variety of organic ingredients employed in the manufacturing of the inks (Zerdoun Bat-Yehuda 1983).…”

“…To date, most of the scientific studies focusing on black writing media deal with iron-gall inks and their corrosion patterns (Rouchon-Quillet et al, 2004;Kolar and Strlic 2006;Rouchon and Bernard 2015), while only a minor part of the ongoing research aims at the characterisation of the materials used in the making of historical inks. Among the latter studies, many deal with the characterisation of inks on manuscripts from the Middle Ages onwards (Hahn et al 2004;Rabin et al 2014;Aceto and Calà 2017;Díaz Hidalgo et al 2018). Similarly, it is well documented that in Antiquity mostly carbon ink was used as a writing material (Lucas 1922;Nicholson and Shaw 2000, pp.…”

Mössbauer Study of Iron Gall Inks on Historical Documents

“…In the past decades, there has been a growing interest in addressing these questions by physical methods that allow non-destructive investigations, sometimes with a high spatial resolution. Proton induced X-ray spectroscopy (PIXE) [4][5][6] and X-ray fluorescence spectroscopy (XRF) [1, [7][8][9][10][11] allow a quantitative analysis of the various elements in written documents on a scale of 0.5 to 3 mm. Attenuated total reflectance (ATR), Fourier transformed infrared (FTIR) [7][8][9] and micro-Raman spectroscopy [1, 7-9, 12, 13] give information on the chemical nature of the organic compounds involved in ink formation and their degradation products.…”

Manuscripts in the Making: Art and Science

“…Some authors employed methodological approaches, often to study historically accurate reconstructions and compositionally-controlled replica samples. Nodari and Ricciardi investigated the influence of different pigments on the ability of FTIR to identify binders in paints laid over parchment [4]; Díaz Hidalgo et al implemented a multi-technique approach, which included Raman and infrared spectroscopy as well as HPLC, to study iron-gall inks [5]; Nabais et al used a combination of microspectrofluorimetry and chemometrics for the identification of medieval lake pigments [6]; and Ali discussed his practice-based research into colourants made from aphid insects and ivy gum, based on medieval recipes [7].…”