Iron Gall Ink Research Articles

Decoding the black essence of Melianthus nectar.

This article is a Commentary on Magner et al. (2023), 239: 2026–2040.

A shadow of ink: Test papers soaked in 4:7-diphenyl-1:10-phenanthroline as a carrier of elemental information for spectrochemical investigations of manuscripts by XRF, LA-ICP-MS and SIMS

In this study, X-Ray Fluorescence Spectrometry (XRF), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Secondary Ion Mass Spectrometry (SIMS) have been used to assess the transfer of ions between iron-gall inks and indicator papers soaked in 4:7-diphenyl-1:10-phenanthroline. Such indicators are commonly used in the conservation practice to detect Fe(II) ions and diagnose a presence of ink corrosion phenomena in historical manuscripts. For this purpose four different model inks with variable Fe:Cu proportions were prepared on the basis of gall nuts extract mixed with FeSO4.7H2O, CuSO4.5H2O and Gum Arabic. Obtained results indicate that apart from the main components of inks (S, Fe and Cu) also other elements can migrate to indicator test papers. Collected XRF and LA-ICP-MS data were consistent in their potential for reconstructing major elemental composition of model inks on the basis of indirect analysis with indicator test papers. LA-ICP-MS extended the range of learning into the trace elemental composition, while SIMS allowed observations of structurally significant fragment ions (ML2+, ML+, M+) where L = 4:7-diphenyl-1:10-phenanthroline and M = Fe or Cu ions.

Changes in color and iron ions of commercial iron gall inks after artificial aging

Iron gall inks consist of vitriols (sulphates of certain metals), gall nut extracts; and gum Arabic: after exposure to oxygen, dark-colored compounds of the inks are formed. As the complexity of the composition of iron gall inks renders documents susceptible to environmental influences, this causes the handwriting thereon to fade. These add technical difficulties to the protection of iron gall inks. Therefore, it is particularly important to understand the changes in the inks during the aging process. For this reason, iron gall ink-stained paper specimens were subject to an intense analytical program to investigate their chemical and physical modifications after aging (temperature/humidity, temperature, and ultraviolet light aging), commercial iron gall ink was used for this experiment, making the study more applicable. The changes of iron gall inks were evaluated using color variation, color density, absorbance, and X-ray photoelectron spectroscopy (XPS). All results indicate that the temperature, humidity, and UV are harmful to the inks in both physical and chemical terms. Physical damage is mainly the aging of the ink color lightening, color density decreases, of which the color of the samples treated with damp heat for 30 days undergoes the greatest change. The chemical change is represented by the ratio of the concentration of iron ions in different valence states, the amount of Fe3+ in the untreated inks is much greater than that of Fe2+, and the amount of Fe2+ exceeds that of Fe3+ after exposure to different methods of aging. Experiments show that UV light causes the most severe damage to handwriting. The main manifestation thereof is color-fade and the paper surface ink part of the iron ion content changes, with the increase of aging time, the Fe2+ content gradually increases. This experimental study of the changes produced by iron gall inks during aging can provide better technical support for the protection of the ink handwriting.

A closer look at the Azzolino collection.

The state of preservation of documents from the historically significant Azzolino collection at the Swedish National Archives has been investigated and analyses carried out of the iron gall inks. The collection shows varied levels of iron gall ink corrosion. An initial visual condition survey was followed by characterisation of the writing ink with XRF spectrometry on a selection of documents. The aim was to investigate whether ink composition could be related to author or geography, and in turn to level of ink corrosion, which could then serve as a basis for decisions on treatment options. Results indicate a relative purity of the inks in this collection in terms of high iron content and low levels of other elements, entailing that elemental analysis is not a good tool to predict potential deterioration of ink in single documents from this historical context. XRF-mapping showed a possibility for discerning authors by ink composition, contributing meaningful information to questions of attribution and historical context for these documents. A tendency for the ink of Queen Christina to contain more copper than inks from the other authors, and the indication that some inks contain calcium, may be of note for further study.

Post-secretory synthesis of a natural analog of iron-gall ink in the black nectar of Melianthus spp.

The black nectar produced by Melianthus flowers is thought to serve as a visual attractant to bird pollinators, but the chemical identity and synthesis of the black pigment are unknown. A combination of analytical biochemistry, transcriptomics, proteomics, and enzyme assays was used to identify the pigment that gives Melianthus nectar its black color and how it is synthesized. Visual modeling of pollinators was also used to infer a potential function of the black coloration. High concentrations of ellagic acid and iron give the nectar its dark black color, which can be recapitulated through synthetic solutions containing only ellagic acid and iron(III). The nectar also contains a peroxidase that oxidizes gallic acid to form ellagic acid. In vitro reactions containing the nectar peroxidase, gallic acid, hydrogen peroxide, and iron(III) fully recreate the black color of the nectar. Visual modeling indicates that the black color is highly conspicuous to avian pollinators within the context of the flower. Melianthus nectar contains a natural analog of iron-gall ink, which humans have used since at least medieval times. This pigment is derived from an ellagic acid-Fe complex synthesized in the nectar and is likely involved in the attraction of passerine pollinators endemic to southern Africa.

Synthetic antioxidants as iron gall ink corrosion inhibitors in historical manuscripts

Synthetic antioxidants as iron gall ink corrosion inhibitors in historical manuscripts

Fractal algorithms and RGB image processing in scribal and ink identification on an 1819 secret initiation manuscript to the “Philike Hetaereia”

Historical texts incorporate important characteristics that need to be assessed including genre, text structure and content. Often overlooked are characteristics of handwritten manuscripts commonly divided into legibility, readability and aesthetics. To determine the scientific feasibility of classification of handwritten texts an objective approach is developed to describe twenty handwritten pages of an 1819 Greek manuscript, that refers to the initiation to the Greek secret “friendly society” (Philike Hetaereia) organization, established as part of the Greek independence against the Ottoman Turks. It is investigated through a fractal and RGB image analysis approach. Fractal Minkowski Dimension was applied on the handwritten text and the RGB color analysis on the ink and paper and both were used as a non-invasive manner and revealed interesting results. The novel RGB image analysis and the fractal analysis of the manuscript identified respectively, five iron gall inks and four scribes from the ink content and handwritten styles, of the compact five lines text and whole text pages. The novel approach was verified with another old manuscript of known ink pigments, as well as with thirteen known handwritten texts of that period and four prints representing modern and similar period texts substantiating the findings of the novel methods.

The making of black inks in an Arabic treatise by al-Qalalūsī dated from the 13th c.: reproduction and characterisation of iron-gall ink recipes

For the first time, this paper systematises the medieval preparation of black writing inks found in the important thirteenth century Andalusian technical treatise written by Muhammad ibn Idrīs ibn al-Qalalūsī (1210–1308). We present the Arabic version of this extraordinary text (‘The gifts of the wise men on the curiosities of the substances’), and its first English translation, as well as discuss key aspects of the processes that remain missing or are unclear indications. In this work, we studied the iron gall inks based on galls, where no other phenolic source is present. In this pedagogical treatise, the recipes for these black iron-gall inks are organised and classified by the gallnuts extraction method used: boiling (decoction), squeezing and infusion, with water being the only solvent used. The inks selected were reproduced and characterised through a multi-analytical approach. Quantification was performed by HPLC–DAD (high performance liquid chromatography with diode array detectors in the UV–VIS), showing that gallic acid is a minor compound in the gall extracts prepared following al-Qalalūsī instructions. In all the recipes, the higher concentration compounds in the gall extracts are the gallotannins pentagalloylglucose and hexagalloylglucose, ranging from 79 to 50% of the phenolic compounds. This supports the results of Raman and infrared spectroscopies. A comparison with medieval Iberian recipes was also done, which served to reinforce our previous results that show water as the sole solvent extracts with much lower yields than mixed solvents (water plus white wine or vinegar).

A holistic approach to understanding the iron-gall inks in the historical documents of the Portuguese Inquisition (1570–1790)

A substantial part of our written heritage is threatened by the fact that much of it has been written using iron-gall ink (IGI). One such example is the documents of the Portuguese Inquisition Tribunals, held by the Arquivo Nacional da Torre do Tombo. Here we present the first systematic analytical approach, using SEM/EDS, µ-FT-IR-ATR and µ-Raman techniques, to characterise fragments from historical records of the Inquisition Tribunals of Évora, Lisboa and Coimbra from the 16th to 18th centuries. The writing ink was identified as IGI, providing complementary compositional data and establishing differences between various formulations of the ink. Additionally, the deleterious effects of the inks-associated degradation phenomena were highlighted. This work allowed understand the writing inks used by this Portuguese institution.

Pigments and Inks Applied in Juan Vespucci’s Portolan Chart (1520)

Not many manuscript maps have been the object of material analysis so far. A portolan chart, signed and dated by Juan Vespucci in 1520, was studied in this research, conserved at the Archivo General de Indias in Seville (Spain). It is made on parchment and depicts the coasts and islands of Europe and Africa. It is the oldest portolan chart made in Seville, being unusual in applying hand stamp for decorative figures. The map was analysed by different non-invasive techniques: infra-red and ultraviolet light, digital microscope and X-ray fluorescence (XRF). The main goals of this study were to identify the materials used, as well as to detect retouching or restoration work. Results showed that the entire parchment was first covered with a white layer made of lead white (Pb), calcite or gypsum (Ca). The principal pigments used were vermilion (Hg), yellow ochre (Fe), azurite (Cu) and a copper-based green pigment (Cu) and carbon black. The letters were probably written with an iron-gall ink (Fe, Cu). Very thin golden leaves were applied on a mixtion glue for gilded wind roses. Several retouches from the 19th/20th centuries were found using zinc and titanium whites and probably cobalt blue.

A Model Iron Gall Ink: An In-Depth Study of Ageing Processes Involving Gallic Acid

Iron gall inks have been among the most used writing materials after carbon black, thus representing an important element of the historical and artistic heritage of our society. Crucially, the preservation of manuscripts and drawings is influenced by the presence of these inks, leading to conservation issues related to paper degradation and text fading. Besides all the advances obtained in paper conservation, the study of iron gall ink's behaviour and ageing is still an important topic, which requires investigation through an accurate molecular characterisation to produce reliable models. In the present work a micro-destructive method based on liquid chromatography techniques (HPLC-DAD and HPLC-ESI-Q-ToF) has been optimised starting from a model gallic acid-based ink. An in-depth study of the behaviour of the ink in time was performed by natural and artificial ageing tests, monitored by colorimetry, showing the autoxidation of gallic acid to ellagic acid in the prepared mock-ups. The effect of relative humidity on ageing processes was also evaluated, allowing us to determine different intermediates depending on the environmental conditions. Finally, the analytical method developed was then successfully applied for investigating 19th-20th century historical ink samples, where one of the identified ageing markers was detected, besides the expected gallic and ellagic acids.

Non-invasive contactless analysis of an early drawing by Raffaello Sanzio by means of optical methods

Studying highly valuable and fragile Renaissance drawings requires a non-invasive contactless analytical approach. In this work, we study an early drawing by Raffaello Sanzio, one of the most important artists of the Italian Renaissance, realized during his stay in Florence (1504–1508). Our analyses aimed to reveal the features of the paper support significant for its dating, identify and map the drawing media to understand the artist’s technical approach, and document the drawing condition with imaging and single-sited optical methods. Reflectance Vis–NIR multispectral imaging spectroscopy elaborated with False-Colour and Principal Component Analysis provided information about the paper support and the drawing media. Laser scanning micro-profilometry and Optical Coherence Tomography allowed revealing the superficial micro-scale features of the support. The chemical composition of the different drawing materials was characterized by μ-Raman spectroscopy, which provided also some evidence of the conservation history of the drawing. Integration of spectroscopic and imaging data shows that Raffaello used different dry drawing media (carbon-based and Pb stylus) to sketch the figure and then refined the details and shadows with iron-gall ink. The paper presents a methodological approach for the analytical examination of fragile paper artworks.

Analysis of Iron Complexes of Tannic Acid and Other Related Polyphenols as Revealed by Spectroscopic Techniques: Implications in the Identification and Characterization of Iron Gall Inks in Historical Manuscripts.

In this work, a structural analysis of the polyphenol complexes with iron and copper at several conditions is reported. The investigated polyphenols were tannic acid, gallic acid, pyrogallol, and syringic acid, being components and molecular models of the gallnuts usually employed in the past in fabrication of iron gall inks (IGIs). Commercial tannic acid extracted from gallnuts, which is a complex mixture of different gallotannins and simpler galloylglucoses, was also employed in this analysis. This analysis comprised the use of Raman, Fourier-transform infrared (FTIR), UV–vis absorption, and fluorescence spectroscopy. The complexation of iron with these molecules leads to a strong change in color due to the deep restructuring of the polyphenol that can be clearly seen by Raman and FTIR spectra. Three main Raman bands appeared at 1450–1490 cm–1 (ν1), 1320–1345 cm–1 (ν2), and 400–650 cm–1 (ν3), which are characteristic of the metal complexes. The structural changes of the polyphenol complexes with iron were also investigated at different pHs and different polyphenol/iron stoichiometries. Other effects of the interaction of polyphenols with iron are the pH decrease of the mixture upon metal complexation and fluorescence quenching induced by the interaction of iron. This quenching is important since it facilitates the Raman inspection of manuscripts since polyphenols show a strong fluorescence emission that overlaps the Raman spectrum. Furthermore, DFT calculations were performed for the first time on the gallic acid complex with iron in order to elaborate a detailed assignment of the vibrational modes of polyphenols and their metal complexes, something that was missed in previous applications of Raman to IGIs.

Ink and support characterization of typologically established papyrus groups from the Palau-Ribes collection

Most of papyrus documents have reached us in a very fragmentary state due to their excavation conditions and, because of the early history of papyrology, without an archaeological contextualisation. Traditionally, papyrologists have only relied on the bibliological characterisation of the documents they work on to provide such a chronological, geographical and socio-cultural context within which to fully understand the texts they edit and study. This study, following previous research on ink characterisation of papyrus documents, uses infrared spectroscopy and SEM/EDX for the analysis of ink and the papyrus surface. To this purpose, 67 samples of coherent groups of papyri from the Palau-Ribes collection in Barcelona, organised according to chronological, geographical and bibliological criteria, have been analysed to identify trends in their composition that may contribute to their characterisation and further enlarge our knowledge of written culture in Antiquity. The samples have been categorised into seven groups: Papyri that are (1) dated to II CE; (2) dated to VI CE; (3) from Oxyrhynchus; (4) from the Monastery of Bawit; (5) written in chancery hands; (6) written in bookhands, and (7) brown ink. All samples have been analysed using infrared spectroscopy, and SEM/EDX has also been used for analysis of a small subset of sample in order to confirm the presence of iron, sulphur and other elements. The results confirm previous findings in iron-gall ink distribution for texts written in bookhands from the Byzantine period, and adds to the characterisation of other groups, such as the Bawit one, with high levels of lignin in the composition of the writing surface, or the degradation of the cellulose shown for the Oxyrhynchus group, suggesting peculiar traits in the manufacturing and conservation of written documents from ancient times.

Sustainable wood electronics by iron-catalyzed laser-induced graphitization for large-scale applications

Ecologically friendly wood electronics will help alleviating the shortcomings of state-of-art cellulose-based “green electronics”. Here we introduce iron-catalyzed laser-induced graphitization (IC-LIG) as an innovative approach for engraving large-scale electrically conductive structures on wood with very high quality and efficiency, overcoming the limitations of conventional LIG including high ablation, thermal damages, need for multiple lasing steps, use of fire retardants and inert atmospheres. An aqueous bio-based coating, inspired by historical iron-gall ink, protects wood from laser ablation and thermal damage while promoting efficient graphitization and smoothening substrate irregularities. Large-scale (100 cm2), highly conductive (≥2500 S m−1) and homogeneous surface areas are engraved single-step in ambient atmosphere with a conventional CO2 laser, even on very thin (∼450 µm) wood veneers. We demonstrate the validity of our approach by turning wood into highly durable strain sensors, flexible electrodes, capacitive touch panels and an electroluminescent LIG-based device.

Insights From the NANOforArt Project: Application of Calcium-Based Nanoparticle Dispersions for Improved Preservation of Parchment Documents

Abstract Following pilot testing of the effects of alkaline-based nanoparticles on modern parchment, the treatment was extended to historical parchment. This paper describes the application and impact of calcium hydroxide and calcium carbonate nanoparticles dispersed in (i) propan-2-ol and (ii) cyclohexane on a parchment book cover dated 1570. The cover showed signs of damage resulting from contact with iron gall inks and low pH values (∼4–5). Protocols for the damage assessment of collagen in parchment as developed in the IDAP project (Improved Damage Assessment of Parchment) were used to evaluate the impact of the conservation treatments on parchment. Preliminary results have shown that the application of calcium-based nanoparticles did not produce any adverse effects on the state of preservation of collagen. In addition, positive outcomes emerged: the pH was re-adjusted to a neutral value, a strengthening and consolidation effect was observed, and the nanoparticles exhibited a protective action upon artificial ageing of the treated parchment.

Visualising iron gall ink underdrawings in sixteenth century paintings in-situ by micro-XRF scanning (MA-XRF) and LED-excited IRR (LEDE-IRR)

Until today, iron gall ink is classified as an exceptional underdrawing material for paintings. Its study and definite identification is usually based on invasive analysis. This article presents a new non-destructive approach using micro-X-ray fluorescence scanning (MA-XRF), LED-excited IRR (LEDE-IRR) based on a narrow wavelength-range of infrared radiation (IR) for illumination and stereomicroscopy for studying and visualising iron gall ink underdrawings. To assess possibilities and limits of these analytical techniques, the approach was tested on panel paintings by Hans Holbein the Elder and Giovanni Battista Cima da Conegliano. Results are compared to invasive examinations on cross-sections using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX). The holistic setup could successfully visualise iron gall ink underdrawings, allowing to harness the formerly invisible underdrawing lines for interdisciplinary studies.

Iron Gall Ink Corrosion on Parchment. Preliminary Evaluation of Treatment Methods Using Aqueous Solutions

Abstract Ink corrosion on parchment is a phenomenon that, unlike its counterpart on paper, has so far been little researched. The same applies to the options for conservation treatment. In order to provide a guide for conservation practice as well as further research, five water-based treatment methods were examined: calcium phytate with pH 5.3 or 3.0, a 0.5% (w/w) solution type B gelatine, a 1% (w/w) solution of phytic acid at pH 2.2 and calcium phytate in combination with gelatine. These were tested on 70 specimens cut from on piece of buffed vellum and 36 specimens from an early modern deed on parchment that showed signs of ink degradation. After treatment and accelerated ageing, the samples were examined with colorimetry and ATR-FTIR spectroscopy and tested with bathophenanthroline for free iron ions. None of the tested treatment methods achieved a fully reliable inhibition of ink corrosion, but apart from a moisture-catalysed acceleration of degradation reactions, no adverse effects were observed either. Results from ATR-FTIR suggest that oxidation plays a more important role in damage related to ink corrosion of parchment than hydrolysis.

Biomedical applications of tannic acid.

Tannic Acid (TA) is a naturally occurring antioxidant polyphenol that has gained popularity over the past decade in the field of biomedical research for its unique biochemical properties. Tannic acid, typically extracted from oak tree galls, has been used in many important historical applications. TA is a key component in vegetable tanning of leather, iron gall ink, red wines, and as a traditional medicine to treat a variety of maladies. The basis of TA utility is derived from its many hydroxyl groups and its affinity for forming hydrogen bonds with proteins and other biomolecules. Today, the study of TA has led to the development of many new pharmaceutical and biomedical applications. TA has been shown to reduce inflammation as an antioxidant, act as an antibiotic in common pathogenic bacterium, and induce apoptosis in several cancer types. TA has also displayed antiviral and antifungal activity. At certain concentrations, TA can be used to treat gastrointestinal disorders such as hemorrhoids and diarrhea, severe burns, and protect against neurodegenerative diseases. TA has also been utilized in biomaterials research as a natural crosslinking agent to improve mechanical properties of natural and synthetic hydrogels and polymers, while also imparting anti-inflammatory, antibacterial, and anticancer activity to the materials. TA has also been used to develop thin film coatings and nanoparticles for drug delivery. In all, TA is fascinating molecule with a wide variety of potential uses in pharmaceuticals, biomaterials applications, and drug delivery strategies.

Vibrational Study (Raman, SERS, and IR) of Plant Gallnut Polyphenols Related to the Fabrication of Iron Gall Inks.

FT-Raman, FTIR, and SERS spectra of the structurally related gallnut polyphenols tannic acid, gallic acid, pyrogallol, and syringic acid are reported in this work aiming at performing a comparative assignation of the bands and finding specific marker features that can identify these compounds in complex polyphenol mixtures. Tannic and gallic acids are the principal components in oak gallnuts, and they can be found in iron gall inks. The different functional groups existing in these molecules and their spatial distribution lead to slight changes of the vibrations. The Raman spectra are dominated by bands corresponding to the ring vibrations, but the substituents in the ring strongly affect these vibrations. In contrast, the FTIR spectra of these molecules are dominated by the peripheral oxygen-containing substituents of the aromatic ring and afford complementary information. SERS spectroscopy can be used to analyze trace amounts of these compounds, but the spectra of these polyphenols show strong changes in comparison with the Raman spectra, indicating a strong interaction with the metal. The most significant modification observed in the SERS spectra of these compounds is the weakening of the benzene 8a ring vibration and the subsequent intensification of the 19a mode of the benzene ring. This mode is also more intense in the FTIR spectra, and its intensification in the SERS spectra could be related to a drastic change in the molecular polarizability associated with the interaction of the polyphenol with the metal in Ag NPs.