Identification Of Pigments Research Articles

Evaluating possible prehistoric cave art in the central Mediterranean: Analyses of pigment traces and identification of taphonomic processes at Għar Ħasan, Malta

The archaeology of the Maltese Islands, particularly the megalithic ‘temple’ structures and underground mass burial sites (hypogea) of the ‘Temple Period’ (ca. 3800 – 2300 BCE), has been the subject of considerable interest. Less is known about the prehistoric use of caves. In particular reports of prehistoric cave art at Għar Ħasan (Hasan’s Cave) have remained controversial, and have been argued to reflect an otherwise unknown pre-Neolithic occupation on the islands.Here, we report a reinvestigation of Għar Ħasan. To distinguish graffiti that have accumulated over the last century and possible older rock art, a range of non-invasive methods were used to determine the chemical properties and colour spectrum of the pigment traces: portable energy-dispersive X-ray fluorescence spectrometry (p-ED-XRF) and visible (VIS) and near-infrared (NIR) spectroscopy. In addition, pigment traces were analyzed with digital microscopy and image enhancement techniques (DStretch).Most of the previously reported cave paintings were shown to have been produced in the last century. One key panel may be older, but vandalism and other destructive processes make a definitive assessment challenging. While we therefore consider the evidence for ‘Palaeolithic’ cave art at Għar Ħasan to be inconclusive, our study also identified complex taphonomic processes that pose severe limitations on the identification of pigment via p-ED-XRF and spectroscopy and can inform and guide future initiatives for rock art conservation.

Mobility-resolved broadband dissociation and parallel reaction monitoring for laser desorption/ionization-mass spectrometry - Tattoo pigment identification supported by trapped ion mobility spectrometry

In this work, trapped ion mobility spectrometry (TIMS) was introduced to facilitate tandem mass spectrometry (MS2) experiments for laser desorption/ionization-mass spectrometry (LDI-MS) as mobility-resolved fragmentation. The mobility separation of desorbed ions was followed by subsequent fragmentation using data-independent broadband collision-induced dissociation (bbCID) or targeted fragmentation through a prototypic version of parallel reaction monitoring-parallel accumulation serial fragmentation (prm-PASEF) for LDI. Both mobility-resolved fragmentation options, TIMS-bbCID and prm-PASEF, were applied to LDI point measurements to identify organic pigments in tattoo inks. Furthermore, the prototypic prm-PASEF algorithm was used in imaging applications to increase confidence in annotating organic tattoo pigments in skin samples with adverse reactions. Due to less complex spectra in matrix-free LDI, both fragmentation methods yielded fast and reliable MS2 identification workflows. TIMS-bbCID was especially beneficial for the rapid acquisition of multiple fragment spectra. For the targeted prm-PASEF approach, analytes’ mobilities needed to be collected prior to simplified fragmentation. Therefore, a reference list for 14 pigments was created. The possible number of experiments per thin section and the associated savings in analysis time compared to conventional MS2 were particularly suitable for the imaging application. Furthermore, the mobility dimension enabled a new orthogonal identification parameter, increasing the annotation confidence of tattoo pigments through compound specific mobilities.

Optical microscopy and SEM-EDS on wall-painting fragments from the St. George’s cathedral at Novgorod

This paper presents the latest data obtained from the analyses of fragments of Russian-Byzantine wall paintings recovered from the architectural excavations carried out in the church of St. George in the Yuriev Princely Monastery built in 1119 at Veliky Novgorod, one of the oldest cities in Russia and UNESCO World site. In the last 7 years the archaeologists of the Institute of Archaeology of the Russian Academy of Sciences in Moscow excavated the 12th century layers and extracted a large number of wall-paintings fragments, which are extremely important for the reconstruction of the history of Novgorod and for the study of Russian-Byzantine art in general. The pigments employed for the paintings and the painting techniques, together with color layers, substrates and mortars, have been studied and analyzed in the last two years in the Laboratory of the Architectural Archaeology and Multidisciplinary Methods for Architectural Research, Institute of Archaeology of the Russian Academy of Sciences. The employed analytical methods were optical microscopy (OM), X-ray Fluorescence Spectrometry (XRF) and Scanning Electron Microscope with Energy Dispersive Spectrometry (SEM-EDS). OM permits to distinguish the superficial painting method, the inclusions in the mortars, the intonaco and intonachino layers and the various substrates. XRF was applied for a first screening of the fragments and for the first pigment identification. The samples of painted mortar were then mounted in epoxy resin and polished for the analysis with SEM-EDS. The analytical data we possessed up to now indicate a very classical Byzantine technique with the use of expensive pigments such as lazurite and cinnabar, but also green earth, various types of ochres and mixtures of pigments. Special care was taken for the identification of the substrates.

Detecting emerald green in 19thC book bindings using vis-NIR spectroscopy.

Detection and identification of heavy metal-based pigments in 19th-century bookbindings is crucial to avoid human user exposure to toxic substances. Vibrant green bookbindings with arsenical emerald green are particularly problematic due to their friability. A pilot study at St Andrews University tested 800 green bookbindings for arsenic presence using visible near-infrared spectrometry, a technique not previously applied to the detection of heavy metals in bindings. The ASD TerraSpec Halo portable spectrometer that is normally used in geology to identify minerals in rocks, is used here to collect hyperspectral reflectance data between 350 and 2500 nm. Raman spectroscopy and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) are used here to validate hyperspectral test results. The study finds that bookbindings containing emerald green have a distinctive pattern in the visible part of the spectrum that is distinguishable from other green pigments. This finding opens up the possibility for all collecting institutions to test bindings for this toxic compound in a non-destructive, cost-effective and efficient manner.

The "hypopigmented" bitemark: a clinical and histologic appraisal.

So-called "hypopigmented" bitemark patterns, commonly seen but not limited to dark skinned individuals, can be of value in forensic investigations. The process of aging bitemarks observed on skin is controversial and without guidelines. This report analyzes tissue obtained from the site of a hypopigmented bitemark using special histochemical stains for the identification of melanin pigment, and a panel of immunohistochemical markers to aid in the aging process. Histologic evaluation clearly showed that cellular changes in the hypopigmented area were indicative of wound healing that had taken place over a period of time. This validates the hypothesis that a hypopigmented bitemark is an indication of a wound inflicted some days previously. These findings have value in forensic investigations, particularly in cases of suspected long-term physical abuse.

Identification of Photosynthetic Pigments extracted from Phaeodactylum tricornutum as High-Value Bioactive Compounds

The present study intends to provide information about a promising source of unique bioactive compounds and for choosing the favorable growth conditions of the diatom “Phaeodactylum tricornutum” suited to different applications. P. tricornutum was cultivated in the temperature range of 20-35°C, light intensity range of 275-538 μmolm-2s-1 and aeration rate range of 2.5- 3.5 Lmin-1. P. tricornutum extracts were analyzed in terms of photosynthetic pigment composition in comparison with a well-known green microalgae Chlorella miniata using the C18 column. Lutein, canthaxanthin, β-carotene and chlorophyll a were detected in C. miniata whereas in P. tricornutum extracts, chlorophyll a, zeaxanthin and β-carotene were identified. Quantitatively, P. tricornutum was distinguished to have greater amount of chlorophyll-a (113.66 mgmL-1) while C. miniata was predominated with a β-carotene content (14.20 mgmL-1). Considerable amounts of pigments were encountered in all of the P. tricornutum extracts obtained under the varying growth conditions. As the temperature was increased and the light intensity was decreased, the accumulation of chlorophyll a and β-carotene increased at the highest aeration rate. Conversely, at the highest light intensity of 538 μmolm-2s-1 and an aeration rate of 3.0 to 3.5 Lmin-1, the zeaxanthin content was maximized and limited at the temperature values over 27.5°C.

Targeted Discovery of Sorbicillinoid Pigments with Anti-Inflammatory Activity from the Sponge-Derived Fungus Stagonospora sp. SYSU-MS7888 Using the PMG Strategy.

An effective identification and discovery of fungal pigments is very important to illustrate the role of fungal pigments in the life process and conduce to the discovery of new bioactive and edible pigments. The phenotype combined with metabolomic and genomic (PMG) strategy led to the discovery and characterization of three new sorbicillinoid pigments, stasorbicillinoids A-C (1-3), and five known analogues (4-8) from the sponge-derived fungus Stagonospora sp. SYSU-MS7888. Their structures were elucidated by the application of spectroscopic methods (NMR, MS, UV, IR, and ECD) and modified Mosher's method. Compounds 1 and 2 featured novel naphthone nuclei linked by two alkyl side chains possibly undergoing inter- and intramolecular Michael reactions. Compounds 1-8 exhibited potent anti-inflammatory activity with IC50 values in the range of 3.56-22.8 μM. Furthermore, compound 2 inhibited the production of IL-1β, IL-6, and TNF-α in a dose-dependent manner. This study provides an effective strategy to accelerate the discovery of new fungal pigments and further exploration of their potential applications in different fields such as medicine and food industries.

A multidisciplinary approach to investigate the peculiar artistic technique of Scagliola: Modern age decorations in Hadrian’s Villa (Tivoli, Italy)

In the present work, a multi-technique approach was adopted to study and characterize six polychrome decorated elements found in the storerooms of the archaeological site of Hadrian's Villa in Tivoli (Rome). In particular, preliminary microscope observations along with μ-Raman and FT-IR spectroscopies and FESEM-EDS analyses were adopted to identify the used materials and the execution technique. This information could allow placing the artefacts in a chronological context, in particular by evaluating possible coherences with the modern phases of the archaeological site. At first visual observation, both stylistic and technical details suggested that the artefacts had been performed by using Scagliola, a particular and not deeply investigated artistic technique developed in Europe at the end of the XVI century for interior decorations. The acquired information has been compared with data obtained by similar in-situ decorations, found on the vault of the Casino Fede, an XVIII century building of the Villa. The characterization of the constituent materials revealed a rich palette, based on both inorganic and organic pigments, some alteration products, and a massive presence of gypsum in the matrix. These results led to confirm the use of Scagliola technique in the realization of all the artefacts, even though this information is not sufficient to confirm if they belong to the same building. Furthermore, a peculiar result was the identification of arsenic-based pigments as pararealgar and amorphous arsenic sulphide as an orange pigment. In particular, pararealgar was identified as the initial material used for the synthesis of the amorphous pigment, a very rare identification in artworks.

Identification of a novel quinoline-based UV-protective pigment from a psychrotrophic Arctic bacterium.

Psychrotrophs are extremophilic microorganisms that grow optimally in low temperature having many unique bioactive molecules of biotechnological applications. In this study, we characterized a pigment from an arctic bacterium with protective activity towards UV exposure. The present research reports isolation and characterization of a psychrotrophic bacteria, RSAP2, from the soil sample of NyAlesund (78°56"N, 11°54"E), Svalbard, Norway. The strain showed closest 16S rRNA gene sequence similarity (99.9%) with Kocuria indica NIO-1021. RSAP2 is a Gram-positive, coccoid aerobe which produces a yellow pigment. The optimal parameters for pigment production while grown in LB medium were 3% (w/v) NaCl and 4 days of incubation of the culture at 20°C and pH9 with shaking (180 rpm). The pigment was extracted in methanol and acetone (2:1) and further purified through column chromatography. It was characterized by mass spectrometry, UV-visible, fluorescence, IR, 1 H NMR, 13 C NMR spectroscopy and CHNS/O analysis. The pigment has a molecular weight of about 258 daltons and the molecular formula was determined as C15 H18 N2 O2 and is a quinoline derivative. We show that the pigment can protect Escherichia coli against UV-mediated mutagenesis. We further demonstrate that the pigment displays a significant antimicrobial effect and in sublethal concentrations it impairs biofilm formation ability of the model organism Staphylococcus aureus. The pigment of a psychrotrophic Arctic bacterium, most likely a strain of K. indica, was purified and its chemical structure was determined. The quinoline-based pigment has the ability to protect live cells from UV induced damage. Analysis and characterization of this newly isolated quinoline-based pigment is a potential candidate for future application in skin care products.

Genetic dissection of Brassica napus photosynthetic pigment content diversity and identification of loci associated with photoperiod and alkaline soil responses

The photosynthetic pigment content of plants is a key physiological trait as it is closely related to photosynthetic efficiency and crop yield potential, and which is extremely susceptible to environmental factors. However, the genetic factors controlling the photosynthetic pigment content in Brassica napus have not yet been completely elucidated. Here, we performed a genome-wide association study (GWAS) of photosynthetic pigment content using a diversity panel comprising 518 B. napus inbred lines grown in four different soil and light environments. We identified 281 single-nucleotide polymorphisms (SNPs) significantly associated with photosynthetic pigment content-related traits. A total of 46 candidate genes involved in chlorophyll and carotenoid metabolism were identified. The identified SNPs and potential candidate genes may facilitate the study of natural variation in photosynthetic pigment accumulation and provide valuable resources for future high photosynthetic efficiency breeding that will adapt to different soil and light conditions.

A Comparative Study of the Method to Rapid Identification of the Mural Pigments by Combining LIBS-Based Dataset and Machine Learning Methods

Due to the similar chemical composition and matrix effect, the accurate identification of mineral pigments on wall paintings has brought great challenges. This work implemented an identification study on three mineral pigments with similar chemical compositions by combining LIBS technology with the K-nearest neighbor algorithm (KNN), random forest (RF support vector machine (SVM), back propagation artificial neural network (Bp-ANN) and convolutional neural network (CNN) to find the most suitable identification method for mural research. Using the SelectKBest algorithm, 300 characteristic lines with the largest difference among the three pigments were determined. The identification models of KNN, RF, SVM, Bp-ANN and CNN were established and optimized. The results showed that, except for the KNN model, the identification accuracy of other models for mock-up mural samples was above 99%. However, only the identification accuracy of 2D-CNN models reached above 94% for actual mural samples. Therefore, the 2D-CNN model was determined as the most suitable model for the identification and analysis of mural pigments.

Non-destructive and non-invasive methodology for the in situ identification of Mexican yellow lake pigments

According to historical sources, yellow colorants have been used since ancient times; despite this, their identification in textiles, Mesoamerican codices and other colonial documents is still a difficult task to perform. Most of the analytical techniques traditionally employed in the identification of yellow dyes, like HPLC-mass spectrometry, require object sampling, an undesirable and often forbidden procedure when dealing with cultural heritage objects. While some information can be obtained by non-invasive and non-destructive multi-technique analyses with portable equipment (allowing in situ studies); only few works have dealt with the in situ analysis of yellow dyes using such techniques, most of them with unsuccessful results. This is due to a combination of factors, mainly the low concentration of the dye on the object (caused by their high coloring power), their fast degradation, and the similarity of the molecule structures responsible for the yellow hues. In this work we present a non-destructive and non-invasive multitechnique methodology for the in situ analysis of Mexican yellow lake pigments with portable equipment: Raman spectroscopy, colorimetry, and fiber optic reflectance spectroscopy (FORS), as well as UV, false color infrared (FCIR) and false color ultraviolet imaging. The colorant specimens studied include: zacatlaxcalli (Cuscuta tinctoria), xochipalli (Cosmos sulphureus), annatto (Bixa orellana), old fustic (Maclura tinctoria), marigold (Tagetes erecta), sweet-scented marigold (Tagetes lucida) and weld (reseda luteola), the latter of European origin. The results presented in this paper shed some light on the non-destructive identification of yellow lake pigments - elaborated with the Mexican traditional specimens mentioned above - with the aim to allow their in situ identification on original artworks.

Natural Substrates and Culture Conditions to Produce Pigments from Potential Microbes in Submerged Fermentation

Pigments from bacteria, fungi, yeast, cyanobacteria, and microalgae have been gaining more demand in the food, leather, and textile industries due to their natural origin and effective bioactive functions. Mass production of microbial pigments using inexpensive and ecofriendly agro-industrial residues is gaining more demand in the current research due to their low cost, natural origin, waste utilization, and high pigment stimulating characteristics. A wide range of natural substrates has been employed in submerged fermentation as carbon and nitrogen sources to enhance the pigment production from these microorganisms to obtain the required quantity of pigments. Submerged fermentation is proven to yield more pigment when added with agro-waste residues. Hence, in this review, aspects of potential pigmented microbes such as diversity, natural substrates that stimulate more pigment production from bacteria, fungi, yeast, and a few microalgae under submerged culture conditions, pigment identification, and ecological functions are detailed for the benefit of industrial personnel, researchers, and other entrepreneurs to explore pigmented microbes for multifaceted applications. In addition, some important aspects of microbial pigments are covered herein to disseminate the knowledge.

A multi-analytical approach for the characterization of materials, manufacturing process and damage mechanisms of wall paintings in Samye Temple, Tibet

This research focuses on the multi-technique characterization and identification of degradation mechanisms of the wall paintings at the Samye Temple in Tibet, which is considered the first built temple of Tibetan Buddhism with an enormous cultural significance to the region. Wall painting general stratigraphy was thoroughly analyzed by Optical Microscopy (OM), Scanning Electron Microscopy – Energy Dispersive X-Ray Spectroscopy (SEM-EDS) and X-ray Powder Diffraction (XRD). Results reveal a clear sequence, from the interior to the surface, consisting on an adobe wall support, a coarse mud plaster, a fine mud plaster, a white ground layer, a surface paint layer, and a coating layer. The identification of natural and/or synthetic pigments and possible re-painted areas was analyzed by polarized light microscope and SEM-EDS, and subsequently studied using Raman spectroscopy. Results reveal the mineral pigments include red cinnabar (HgS) and red lead (Pb3O4), blue azurite (Cu3(CO3)2(OH)2), green malachite (Cu2CO3(OH)2), yellow orpiment (As2S3), and a gold layer (gold powder). White and black pigments are magnesite (MgCO3) and carbon, respectively. Additionally, the external surface coating varnish found on the top of the paint layer was also analyzed by Transmission Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance mode (FTIR-ATR), Proton Nuclear Magnetic Resonance (H1 NMR), Thermogravimetric analysis (TG), Mass Spectrometry (MS) and SEM-EDX analysis. Results show main components of this coating include acrylates and, possibly, silanes, revealing a recent conservation intervention activity. The hydric expansion/contraction of clay minerals in the adobe support and mud plaster layers and the rigid and impervious acrylate coating layer could have accelerated the deterioration and be the responsible for the development of cracks both at the interface of the different support layer and normal to the wall painting surface, resulting in massive losses. These findings are relevant to better understand the traditional manufacturing process of historic wall paintings in Tibet, which is not fully understood yet, and serve to further conservation activities of this historically rich temple.

Automated Identification of Incomplete and Complete Retinal Epithelial Pigment and Outer Retinal Atrophy Using Machine Learning

To assess and validate a deep learning algorithm to automatically detect incomplete retinal pigment epithelial and outer retinal atrophy (iRORA) and complete retinal pigment epithelial and outer retinal atrophy (cRORA) in eyes with age-related macular degeneration. In a retrospective machine learning analysis, a deep learning model was trained to jointly classify the presence of iRORA and cRORA within a given B-scan. The algorithm was evaluated using 2 separate and independent datasets. OCT B-scan volumes from 71 patients with nonneovascular age-related macular degeneration captured at the Doheny-University of California Los Angeles Eye Centers and the following 2 external OCT B-scans testing datasets: (1) University of Pennsylvania, University of Miami, and Case Western Reserve University and (2) Doheny Image Reading Research Laboratory. The images were annotated by an experienced grader for the presence of iRORA and cRORA. A Resnet18 model was trained to classify these annotations for each B-scan using OCT volumes collected at the Doheny-University of California Los Angeles Eye Centers. The model was applied to 2 testing datasets to assess out-of-sample model performance. Model performance was quantified in terms of area under the receiver operating characteristic curve (AUROC) and area under the precision-recall curve (AUPRC). Sensitivity, specificity, and positive predictive value were also compared against additional clinician annotators. On an independently collected test set, consisting of 1117 volumes from the general population, the model predicted iRORA and cRORA presence within the entire volume with nearly perfect AUROC performance and AUPRC scores (iRORA, 0.61; 95% confidence interval [CI] [0.45, 0.82]: cRORA, 0.83; 95% CI [0.68, 0.95]). On another independently collected set, consisting of 60 OCT B-scans enriched for iRORA and cRORA lesions, the model performed with AUROC (iRORA: 0.68, 95% CI [0.54, 0.81]; cRORA: 0.84, 95% CI [0.75, 0.94]) and AUPRC (iRORA: 0.70, 95% CI [0.55, 0.86]; cRORA: 0.82, 95% CI [0.70, 0.93]). A deep learning model can accurately and precisely identify both iRORA and cRORA lesions within the OCT B-scan volume. The model can achieve similar sensitivity compared with human graders, which potentially obviates a laborious and time-consuming annotation process and could be developed into a diagnostic screening tool.

Pigment-based chemotaxonomy of the phytoplankton community from a marine mussel farming area

Microscopy technique is traditionally employed for assessing phytoplankton taxonomy. However, chemical approaches, such as the identification of biomarker pigments, allow to elucidate microalgae groups more quickly, in addition to detecting these valuable compounds. This study aimed to identify the pigment profile of microalgae species and to determine the seasonal pigment fluctuation in a marine mussel farm. Water samples were collected periodically between the years of 2014 and 2015. Phytoplanktonic organisms were isolated and cultivated in f/2 liquid medium under controlled temperature and light cycle. Cell content extracts from each unialgal culture and water sample were analyzed by High Performance Liquid Chromatography (HPLC). Pigment profiles of 13 marine microalgae strains were identified (12 Diatoms and 1 Dinoflagellate). Chlorophyll a and fucoxanthin were most present in Diatoms, while peridinin was the major carotenoid in Prorocentrum micans. Bacillariophyceae had higher density in the summer and fall. Dinophyceae, Cryptophyceae, Euglenophyceae, Prasinophyceae, Dictyophyceae and Ebriidea, had an increase in density during winter and spring. Following the trend of phytoplankton groups, pigments such as fucoxanthin, zeaxanthin, diadinoxanthin, chlorophyll c3 and c2, were identified throughout the year. Prasinoxanthin, peridinin, dinoxanthin and antheraxanthin were identified in samples collected during winter and spring.

Red wine coloration: A review of pigmented molecules, reactions, and applications.

Color is one of the most distinctive qualities of red wine. Despite new knowledge in the field of pigment identification, copigmentation, and oxidation being forthcoming, there is still a large gap between the fundamental research and practical winemaking outcomes. A state-of-art review from these two aspects is, therefore, necessary. This review first introduces updated knowledge about the primary pigments in wine, with emphasis on their physicochemical properties. Then, the mechanisms of copigmentation and oxidation are elucidated in detail, along with their relative contributions to wine color. Finally, the practical effects of copigmentation and micro-oxygenation (MOX) in winemaking are summarized and discussed. In general, wine coloration is ultimately determined by the anthocyanin flavylium cation, which is greatly influenced by wine pH. In young red wine, grape-derived anthocyanins and nonanthocyanin polyphenols (as copigments) are the foundation for wine coloration. During aging and storage, anthocyanin derivatives are formed via various chemical reactions, where moderate oxidation plays a vital role, whereas copigmentation constantly decreases. The essence of wine color evolution relates to the changes of physicochemical properties of primary pigments in wine, where the hydration equilibrium gradually diminishes. In practice, the effects of copigment addition and MOX during real vinification can be viewed as somewhat controversial, considering that many studies showed different effects on wine color and pigment concentration. Universal features can be summarized but some phenomena still remain unclear and deserve further exploration.

Analytical studies on commercial artists’ colour charts from Das Deutsche Farbenbuch (1925)—identification of synthetic and natural organic colourants by Raman microscopy, surface-enhanced Raman spectroscopy and metal underlayer ATR-FTIR spectroscopy

Historical colour charts provide a rich and often well-dated reference materials source for studying the chemical composition of all kinds of commercial brands of artists’ paints. This article presents the results of an extensive analytical study of more than 80 paint hues from 11 colour charts that are included in the German standard book Das Deutsche Farbenbuch by H. Trillich (1925, Part II). Our research focused on the identification of synthetic organic pigments, whose quickly increasing significance for artists’ paints in the early twentieth century is impossible to evaluate by documentary source research alone. A stepwise procedure combining different non- or minimally invasive vibrational spectroscopy techniques—Normal Raman and Surface-Enhanced Raman spectroscopy as well as Metal Underlayer Attenuated Total Reflection Fourier-transform Infrared Spectroscopy—allowed the identification of 18 different organic colourants in artists’ watercolours, tempera and oil colours from six German manufacturers. In addition, micro-X-Ray Fluorescence spectroscopy was applied to determine the elemental pattern of substrates, fillers, and admixed inorganic pigments. In addition to a few traditional natural organic colourants (dark and rose madder lake, cochineal lake), most of the identified compounds comprised synthetic organic pigments or synthetic dyes from various chemical classes (indigo, anthraquinone, monoazo, ß-naphthol, xanthene, triarylcarbonium, nitroso, and azine compounds). Some of these have not or only rarely been reported in artists’ paints so far. Since the identified organic colourants have mainly poor to fair (only sometimes good) fastness to light according to modern standards and partially also to solvents typically used in conservation treatments, it is evident that works of art from this period should be treated keeping in mind the possible presence of such colourants, when planning both interventive treatments and preventive measures.

Fast identification of mural pigments at Mogao Grottoes using a LIBS-based spectral matching algorithm

To quickly identify the mineral pigments in the Dunhuang murals, a spectral matching algorithm (SMA) based on four methods was combined with laser-induced breakdown spectroscopy (LIBS) for the first time. The optimal range of LIBS spectrum for mineral pigments was determined using the similarity value between two different types of samples of the same pigment. A mineral pigment LIBS database was established by comparing the spectral similarities of tablets and simulated samples, and this database was successfully used to identify unknown pigments on tablet, simulated, and real mural debris samples. The results show that the SMA method coupled with the LIBS technique has great potential for identifying mineral pigments.

Anthocyanins, Carotenoids and Chlorophylls in Edible Plant Leaves Unveiled by Tandem Mass Spectrometry.

Natural pigments are a quite relevant group of molecules that are widely distributed in nature, possessing a significant role in our daily lives. Besides their colors, natural pigments are currently recognized as having relevant biological properties associated with health benefits, such as anti-tumor, anti-atherogenicity, anti-aging and anti-inflammatory activities, among others. Some of these compounds are easily associated with specific fruits (such as blueberries with anthocyanins, red pitaya with betalain or tomato with lycopene), vegetables (carrots with carotenoids), plant leaves (chlorophylls in green leaves or carotenoids in yellow and red autumn leaves) and even the muscle tissue of vertebrates (such as myoglobin). Despite being less popular as natural pigment sources, edible plant leaves possess a high variety of chlorophylls, as well as a high variety of carotenoids and anthocyanins. The purpose of this review is to critically analyze the whole workflow employed to identify and quantify the most common natural pigments (anthocyanin, carotenoids and chlorophylls) in edible plant leaves using tandem mass spectrometry. Across the literature there, is a lack of consistency in the methods used to extract and analyze these compounds, and this review aims to surpass this issue. Additionally, mass spectrometry has stood out in the context of metabolomics, currently being a widely employed technique in this field. For the three pigments classes, the following steps will be scrutinized: (i) sample pre-preparation, including the solvents and extraction conditions; (ii) details of the chromatographic separation and mass spectrometry experiments (iii) pigment identification and quantification.