The study of mixed ink recipes has a broad interest since along the millennial historical transition from carbonbased inks to iron-gallate inks, mixed carbon-iron gallate might represent a long transitional phase. The knowledge of the impact and interaction of chemical and microbiological agents with the tangible archivistic heritage strengthens our ability to preserve historical documents over time. Herein, we propose a multianalytical approach including optical and electron microscopies, vibrational spectroscopies, liquid chromatography with mass spectrometric detection. Moreover, microorganism isolation and characterization were carried out on selected samples. Our case study (Vanvitellian letters) demonstrates that, in the presence of carbon black, integration of spectroscopic technique with HPLC-MS/MS analysis is essential for the proper characterization of iron-gallate complex and its degradation products. Therefore, we propose and apply a protocol in which a Raman-based pre-screening easily detects carbon black in ink, and, in case of carbon black presence, HPLC-MS/ MS is required to verify gallic acid/oxidation sub-products, to correctly assign the ink to the mixed recipe. Both ink formulation details and warnings on the diagnostics of mixed carbon-iron gall inks arise from the present study, calling for further investigation into their degradation mechanisms.

The spread of logwood bark (Heamatoxylum campechianum L.) in Europe as a dyestuff dates back to the 16th century, while its integration into ink formulations only began in the 19th century (logwood inks). Renowned for their broad spectrum of achievable colours and their non-corrosive impact on paper, logwood inks have been used by many artists, for instance by Impressionists in their drawings. This work investigates the gap in the literature related to the chemical composition of logwood-based inks, specifically focusing on the comprehensive characterisation of dye components and the influence of recipes on the inks molecular profile. Several 19th-20th century formulations of logwood inks, differing in inorganic salts, additives and pre-oxidation time, were selected and reproduced according to historical recipes. Colourimetric measurements enabled us to evaluate the chromatic differences of logwood-based inks produced following historical methods. Instead, the organic component was investigated on reference mock-ups by analytical methods based on micro-Raman spectroscopy and liquid chromatography coupled to diode array detection (HPLC-DAD) and high-resolution tandem mass spectrometry (HPLC-ESI-Q-ToF) after suitable sample treatments. Raman analysis revealed significative shifts in vibrational modes of dyes depending on the inorganic salts used in the recipes, providing a unique fingerprint able of distinguishing alum-, alum/copper-, iron-, and chrome-based logwood inks. Additionally, HPLC-DAD and HPLC-ESI-Q-ToF enabled us to expand the dataset of molecular markers available for logwood inks identification, by tentatively assigning the structure of compounds never or seldom reported in the literature (G-compounds and hematein derivatives). The potential synergy of spectroscopic and chromatographic techniques was also explored, allowing us to achieve valuable insights on the oxidation pathway of hematoxylin to hematein (both C.I. 75290) in relation to the ink recipes. The proposed method is particularly valuable in forensic and heritage science, where the composition of inks can offer crucial insights into the origin and authenticity of documents or artworks.

In 1900, Francis Herbert Jennison’s book The Manufacture of Lake Pigments from Artificial Colours was published in London. In the early 20th century, the technical literature focussing on synthetic dyes mainly dealt with their use for dyeing. Conversely, the literature on lake pigment manufacture is less comprehensive, and Jennison’s publication was the first monograph on this topic. His book comprises descriptions of the dyes, substrates, and various methods for lake making. Practical examples complete the work: sixteen colour plates with original samples of lake pigments showcase the practical effect on colour of the different dyes and preparation methods. Herein, we present an overview of the context of Jennison’s research and delve into a selection of formulations. Green lake pigment plates were sampled and analysed by liquid chromatography coupled with spectroscopic and spectrometric detectors and by X-ray fluorescence spectroscopy to correlate the chemical composition with the recipes reported in the book. Seldom or no longer used and unexplored historical dyes were detected, along with polyphenolic compounds possibly used as precipitating agents in lake pigment formulations. Moreover, the examination of two different editions of the Jennison manuscript (i.e., the English and German books) revealed different chemical profiles corresponding to the same lake pigment formulation. This emphasizes the significance of Jennison’s book, confirming how understanding of early formulations is needed to elucidate the later ones.

Acid synthetic organic pigments (SOPs), namely water-soluble anionic compounds containing acidic groups (e.g. - SO3H, -NO2, etc), were introduced into artistic materials in the late 19th century. SOPs were often combined in highly complex mixtures to achieve the desired colours, and therefore, chemical analysis requires ultra-selective and ultra-sensitive methods such as reversed-phase liquid chromatography coupled with mass spectrometric detectors. However, acid SOPs produce chromatographic tailing, leading to loss of resolution and sensitivity. To improve their detection, in this work an approach based on liquid chromatography coupled to a diode array detector and high-resolution mass spectrometry (HPLC-DAD-HRMS) was optimized. The study was carried out using standard acid SOPs (Amido naphthol red G, Cotton scarlet, and Naphthol yellow S), also assessing the effect of chromatographic parameter modification on a selection of natural dyes (Carminic acid, Alizarin, and Purpurin) and basic SOPs (Methylene blue and Methyl violet). Starting from a chromatographic gradient optimized for the analysis of tannins in iron gall inks, different flow rates and mobile phase modifier (formic acid) concentration were tested. The chromatographic efficiency (number of theoretical plates, NTP), resolution (R), symmetry factor (SF), ionisation efficiency (IE), signal-to-noise ratio (SNR), limit of detection (LOD) and limit of quantification (LOQ) were evaluated for each analyte. This enabled us to determine the optimal chromatographic conditions for the analysis of acid dye-based artistic materials (gradient with water with 1% v/v formic acid (FA); acetonitrile with 0.3% v/v FA; flow rate = 0.6 mL/min). Finally, the optimized method was applied for the investigation of organic dyes in a Persian carpet, and proved effective in improving both sensitivity and selectivity of the target analytes in a complex matrix. This study not only provides us with a chromatographic method that could be universally valid for the analysis of historical and contemporary artistic materials, but also caters to the difficult chromatographic separation of acid dyes in food, environmental, and forensic chemistry.

Sol LeWitt, a pioneer of conceptual art, created during his career over 1350 wall drawings, including the Wall Drawing #736 (1993) at the Center for Contemporary Art Luigi Pecci in Prato (Prato, Italy). The painting, executed by Andrea Marescalchi and Antony Sansotta under LeWitt’s instructions, features a grid of coloured rectangles obtained by overlapping different layers of inks. During a 2021 restoration by the Wall Paintings and Stuccoes Department of the Opificio delle Pietre Dure (Firenze, Italy), an in-depth investigation of the composition and the materials used by LeWitt’s assistants in producing Wall Drawing #736 was performed. A multi-analytical approach entailing Raman spectroscopy, high-performance liquid chromatography coupled to diode array and high-resolution mass spectrometry, gas chromatography–mass spectrometry (GC–MS), and pyrolysis coupled with GC–MS was applied. Our results revealed the use of animal glue, shellac resin, paraffin wax, linseed oil, and various organic pigments. The binder in the preparation layer was identified as poly(vinyl acetate), while poly(n-butyl methacrylate) was determined as a fixative. This research provided valuable insights into LeWitt’s techniques. The acquired knowledge on the paint technique is highly relevant in supporting conservators in restoration and consolidating the many wall drawings produced exploiting the same technique all over the world.

Several manuscripts and drawings of our historical and artistic heritage have been produced with iron gall inks. To obtain an iron gall ink, ancient treatises cite the addition of ferrous sulphate and gum Arabic to a decoction of oak galls as a basic procedure. Owing to the development of synthetic chemistry, iron gall ink recipes were improved with new materials and procedures in the late 19th and early 20th century. Notably, many conservation issues arise from the interaction between iron gall inks and the paper support of manuscripts and drawings. To date, most of the research on the topic are focused on paper preservation by non-destructive analytical methods, which provide only limited information on degradation process trends and minor components, representative of iron gall ink's recipes. In the present work, three historical recipes of iron gall inks (alizarine ink, Reid ink, modern gall ink), dated to 19th-20th century and differing for the preparation method and additives, were characterized. The molecular markers of iron gall inks and of gallic acid degradation were detected by an optimized protocol based on high performance liquid chromatography coupled to high resolution mass spectrometry (HPLCHRMS). Furthermore, by performing ageing tests on reference materials in different indoor conditions (natural light and stored in the dark), two degradation mechanisms were observed: hydrolysis of poly-galloyl glucose species and auto-oxidation of gallic acid. Thus, different chemical profiles and ageing trends were revealed depending on the starting recipe. The procedure Limit of Detection (LOD) was estimated, improving the approaches reported so far in the literature. Finally, the strategy was successfully applied for the characterisation of the ink employed in a very degraded 16th century manuscript, granting access to the complete molecular profile of an iron gall ink with just 15 µg of sample.

The finding of numerous synthetic strategies between the 19th and 20th century fostered the production of an extensive spectrum of organic dyes for artistic and industrial applications. Shortly after, challenges emerged related to the rapid deterioration of these products. Nowadays, the characterization of coloured pieces of art produced in the first half of the XXth century is further complicated by the absence of reference materials with an unambiguous composition, which are frequently a mixture between the starting dyes and their degradations products. Here we demonstrate as Surface Enhanced Raman Spectroscopy coupled with the simplest separation technique, i.e. Thin Layer Chromatography, is able beyond to recognize several synthetic dyes also to identify their isomers and degradation products. The occasion was the study of a catalogue of dyed textile swatches, produced in 1951 by the well-known Italian industry ACNA (Azienda Coloranti Nazionali e Affini). An apparently easy task turned out to be, indeed, not at all obvious as we found out that the actual composition of the reference samples seldomly corresponded to the declared one. TLC-SERS investigation of historical textile swatches was complemented by the integration of liquid chromatography coupled with a diode array detector and high-resolution mass spectrometry (HPLC-DAD-HRMS). This approach allowed us to validate the findings of TLC-SERS and to distinctively characterise synthetic by-products and degradation markers resulting from the deterioration of the dyes.

Man has always used writing to be able to communicate, express, and disseminate his thoughts. In time, many different coloured extracts of plant and animal origin have been used to produce inks; after the development of synthetic chemistry, artificial and synthetic dyes started to be widely exploited. The end of the 19th century marked great technological and industrial innovations in commercial production of artists' materials. To reveal ink formulations and build a database of red inks by different producers, we developed a multi-analytical approach and investigated a collection of writing inks produced in France in the late 19th – early 20th century. The materials used as binders, additives, dyes, and pigments have been investigated by high performance liquid chromatography coupled with diode array and tandem mass spectrometric detectors (HPLC-DAD-MS2), in situ derivatisation pyrolysis coupled with gas chromatography-mass spectrometry (Py(HMDS)-GC/MS), surface enhanced Raman (SERS, TLC-SERS) and X-Ray Fluorescence spectroscopies. Several dyes and pigments were detected, showing that the French ink's formulations of the early days of synthetic dye industry were based on rhodamine B and 6G, eosin Y, rose Bengal and methyl or crystal violet. Instead, as binder and additives only gum Arabic and shellac resin have been identified, respectively. Mass spectrometry also allowed us to detect possible by-products of the synthesis of ink's dyes and even early degradation products, that can be used for ink identification in historical writings and drawings. Our studies can pave the way to investigate inks in historical samples by introducing ultra-sensitive chromatographic and mass spectrometric methods in the array of analytical tools available to the chemist.

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.