Lake Pigments Research Articles

Non-invasive identification of traditional red lake pigments in fourteenth to sixteenth centuries paintings through the use of hyperspectral imaging technique

The present paper, which focuses on the identification of red lake pigments, in particular madder, brazilwood, and cochineal, addresses the advantages and drawbacks of using reflectance hyperspectral imaging in the visible and near-infrared ranges as a non-invasive method of discrimination between different red organic pigments in cultural heritage objects. Based on reconstructions of paints used in the period extending from the fourteenth to the sixteenth century, prepared with as far as possible historical accuracy, the analyses by means of visible/near-infrared reflectance hyperspectral imaging were carried out with the objective of understanding the most significant differences between these vegetal- and animal-based red lake pigments. The paper discusses the results that were obtained on four original Italian and North European paintings and compared with those from the paint reconstructions, in order to demonstrate how the hyperspectral imaging technique can be usefully and effectively applied to the identification and mapping of red lake pigments in painted surfaces of interest in the conservation field.

Natural Colorants for Dyeing and lake Pigments

Reseña del libro Natural Colorants for Dyeing and lake Pigments. Autores: Jo Kirby, Maarten van Bommel, André Verhecken Publicado por: Archetype Publications Ltd con CHARISMA Londres, 25 de Octubre de 2014 114 páginas, 208 x 297mm Idioma: Inglés ISBN-10: 1909492159ISBN-13: 978-1909492158

Implementation of a neural network for multispectral luminescence imaging of lake pigment paints.

Luminescence multispectral imaging is a developing and promising technique in the fields of conservation science and cultural heritage studies. In this article, we present a new methodology for recording the spatially resolved luminescence properties of objects. This methodology relies on the development of a lab-made multispectral camera setup optimized to collect low-yield luminescence images. In addition to a classic data preprocessing procedure to reduce noise on the data, we present an innovative method, based on a neural network algorithm, that allows us to obtain radiometrically calibrated luminescence spectra with increased spectral resolution from the low-spectral resolution acquisitions. After preliminary corrections, a neural network is trained using the 15-band multispectral luminescence acquisitions and corresponding spot spectroscopy luminescence data. This neural network is then used to retrieve a megapixel multispectral cube between 460 and 710 nm with a 5 nm resolution from a low-spectral-resolution multispectral acquisition. The resulting data are independent from the detection chain of the imaging system (filter transmittance, spectral sensitivity of the lens and optics, etc.). As a result, the image cube provides radiometrically calibrated emission spectra with increased spectral resolution. For each pixel, we can thus retrieve a spectrum comparable to those obtained with conventional luminescence spectroscopy. We apply this method to a panel of lake pigment paints and discuss the pertinence and perspectives of this new approach.

Identification by HPLC-DAD and SEM-EDX Analyses of Lake Pigments from Helichrysum arenarium

Identification by HPLC-DAD and SEM-EDX Analyses of Lake Pigments from Helichrysum arenarium

Combined approach of FT‐Raman, SERS and IR micro‐ATR spectroscopies to enlighten ancient technologies of painted and varnished works of art

The characterization of materials involved in painted works of art provides a better knowledge of artworks through the understanding of artistic and technological processes. In this study, some pieces selected from a large corpus of French Decorative Arts objects from 18th century museum collections were analyzed. These materials are complex system made of a multilayered colored background, covered with varnish layers. Colored or gilded ornaments are applied, representing different characters, flowers or landscapes, then varnished again. The aim of this study was to improve the painting and varnishing techniques knowledge in the Decorative Arts field during the 18th century. Vibrational spectroscopies, Raman, surface enhanced Raman spectroscopy (SERS) and infrared, were used to analyze some specific parts of these objects, especially organic materials such as lake pigments, binders and varnishes, and some of them were identified. For this purpose, a set of experimental setups and parameters were used according to the samples. The performed analyses were thus done using conventional FT‐Raman at 1064 nm, SERS with a 458 nm excitation wavelength, infrared using a micro‐ATR mode, and by defining for each technique and each analysed sample the best set of analytical parameters. The results obtained are all complementary and allowed us to completely identify and characterize multilayered paint systems as well as varnish compositions using specific data treatment methodology. This study is a description of the various possibilities that vibrational spectroscopies can provide when the right settings are employed, with a deeper look into the vibrational features using new data treatments. Copyright © 2014 John Wiley & Sons, Ltd.

Surface‐enhanced Raman scattering for the analysis of red lake pigments in painting layers mounted in cross sections

Cross sections are very useful in the scientific investigation of paintings and polychromies as they show the sequence of the layers and allow the detection of colorants in each layer through micro‐Raman spectroscopy. Surface‐enhanced Raman scattering (SERS) presently represents the most promising tool to overcome the limits of a traditional micro‐Raman approach in the investigation of painting materials containing fluorescent organic dyes. Among the SERS substrates, silver colloidal pastes are suitable to analyze minute samples by drop‐coating them with the paste, without the need of specific pre‐treatments. The application of silver colloidal pastes has been explored here on two cross sections obtained from the 13th century painted wooden statue and from the 16th century mural painting.The main issue when employing such a substrate consists in achieving a suitable coating on the complex surfaces under investigation. In this work, some tests were devoted to enable the display of coated samples through the microscope coupled to the Raman spectrometer and to enhance the signals from lake pigments. The analytical procedure was successful in gaining SER spectra from the sections: the red, highly fluorescent pigment grains were identified as lake pigments obtained by kermes and by a purpurin‐rich plant dyestuff. SER signals were discussed by considering SER spectra obtained from pure substances and/or reference materials and data reported in the literature.The work represents a further step toward the possibility of fully exploiting the high spatial resolution of the micro‐Raman spectrometer to investigate samples from painted objects. Copyright © 2014 John Wiley & Sons, Ltd.

A systematic analysis of red lake pigments in French Impressionist and Post‐Impressionist paintings by surface‐enhanced Raman spectroscopy (SERS)

The Art Institute of Chicago (AIC) owns one of the largest and very finest collections of 19th century French Impressionist and Post‐Impressionist paintings in the world. While the palette of the Impressionists has been extensively characterized for what concerns both traditional and innovative inorganic pigments, to date, the identification of the red organic lakes – widely used for their intense, brilliant color – has posed an analytical challenge. In this work, firstly, surface‐enhanced Raman spectroscopy has been applied to the analysis of red lake paint reconstructions prepared according to 19th century historical recipes. Results demonstrated that dye identification can be successfully accomplished on Lee–Meisel colloids after hydrolysis with hydrofluoric acid, even when inorganic pigments, extenders, ground materials or binding media are associated with the red lake in the sample analyzed. Subsequently, the same protocol was used to examine samples from Manet, Pissarro, Renoir, Monet and Gauguin paintings in the AIC collection. Results showed the predominant use of madder and cochineal lakes, sometimes in combination, thus greatly enhancing our knowledge of the Impressionist usage of different types of red lakes. Copyright © 2014 John Wiley & Sons, Ltd.

Study of materials and techniques in painted ceiling panels from a palace in Cremona (Italy, 15thcentury)

Abstract Background This study concerns the analysis of four painted wooden panels from the second half of the 15th century which embellish the ceiling of a palace situated in Cremona (Northern Italy). This type of painting was generally used to decorate the top of the walls and the ceilings of the rooms in aristocratic palaces and they usually portray the owner’s ancestors, family members or important visitors. The paintings are of historical importance since they enable us to study the clothing and hair styles which were in fashionable in Italy during the Renaissance. These panels were heavily damaged and required a lot of restoration including the cleaning of the paint layers. This enabled us to carry out a thorough examination of the materials and techniques used for creating these paintings. Results Various micro-samples were taken in order to distinguish the materials and, in particular: (i) to analyze the ground layer and study its function; (ii) to typify the organic binders and the pigments of the polychrome films. The stratigraphic sequence of micro-samples was analyzed using optical microscopy, the elemental composition was determined by means of the SEM-EDX technique while the organic binders were analyzed by means of μFT-IR spectroscopy. The main component of ground layer proved to be clay. The organic binder was probably composed of a protein-based material such as animal glue. This type of ground layer is similar to the traditional 15th century Flemish formula and seems to confirm the strong influence of that artistic technique in Northern Italy. Cross-section investigation showed a primer layer over the ground layer made of white lead pigment. In fact, a white primer was used to cover the ground layer of yellowish clay common in Central Europe. The importance of this research is also confirmed by the study of paint films, for which pigments such as azurite or cinnabar were used. Red lake pigment for painting the subjects’ complexions was emphasized. Conclusions The analyses provide new detailed information concerning the materials used for painting the ceiling panels, the layer sequence of the paints and Northern Italian 15th century painting techniques.

Environmental and complexation effects on the structures and spectroscopic signatures of organic pigments relevant to cultural heritage: the case of alizarin and alizarin-Mg(II)/Al(III) complexes.

An integrated computational approach allowed an unbiased analysis of optical and structural properties of alizarin-based pigments, which can be directly compared with experimental results. Madder lake pigments have been modeled by Mg(II)- and Al(III)-coordinated alizarin taking into account solvation and metal-linkage effects, responsible for colour modifications. Moreover, different environmental conditions have been analyzed for free alizarin, showing in all cases semi-quantitative agreement with experimental spectroscopic data (UV-VIS). Our results point out the ability of in silico approaches to unravel the subtle interplay of stereo-electronic, dynamic, and environmental effects in tuning the physico-chemical properties of pigments relevant to cultural heritage.

Structure elucidation and chromatographic identification of anthraquinone components of cochineal (Dactylopius coccus) detected in historical objects

Cochineal is one of the most well known organic red dyes. Dactylopius coccus Costa (Dactylopiidae) is a scale insect that is used as the source of the dye known as Mexican cochineal. Although cochineal is today a natural food colorant (E120) and although it has been used in art objects (textiles and paintings) for centuries, its exact chemical consistency is not well clarified except for carminic acid which is the major component and kermesic and flavokermesic acids. Several minor components (typically less than 5% of the colouring material) remained unknown or partially studied, although their presence has been reported in numerous analytical works related to art objects. Chemical investigation of the methanol extract of the dried insects, after subsequent HPLC chromatographic separations, led to the isolation and structure elucidation of six new anthraquinones, along with the known compounds carminic acid, kermesic acid and flavokermesic acid. The new compounds formerly described as DCII and DCIII, were found to be the 2-C-glucoside of flavokermesic acid and 4-aminocarminic acid, respectively, while DCIV and DCVII were found to be the α/β C-glucofuranosides of kermesic acid, and were studied as a mixture due to equilibrium. In addition, 3-O-glucoside of flavokermesic acid (DCOFK), and 3,4-dideoxycarminic acid (DDCA) were identified. The structures of the new compounds were elucidated on the basis of their NMR and MS data. Finally, the new compounds were detected in silk dyed with cochineal, lake pigment and, furthermore, in historical objects of the cultural heritage (icon and textile) using LC–DAD and LC–MS.

Surface-enhanced Raman spectroscopy studies of yellow organic dyestuffs and lake pigments in oil paint

Identifying natural, organic dyes and pigments is important for the conservation, preservation, and historical interpretation of works of art. Although previous SERS studies have demonstrated high sensitivity and selectivity for red lake pigments using various pretreatment conditions, corresponding investigations of yellow lake pigments and paints are relatively sparse. Here, surface-enhanced Raman scattering (SERS) spectroscopy is used to identify a variety of yellow organic dyestuffs and lake pigments in oil paint. High-quality SERS spectra of yellow dyestuffs (i.e., turmeric, old fustic, Buckthorn berries) and corresponding paints could be obtained with or without sample pretreatment using microliter quantities of HCl and methanol at room temperature. However, the SERS spectra of yellow lake pigments (i.e., Stil de Grain, Reseda lake) and their corresponding oil paints were only observed upon sample pretreatment. Ultimately, we demonstrate a reliable sample treatment protocol for SERS-based identification of turmeric, old fustic, Buckthorn berries, Stil de Grain, and Reseda lake as well as for microscopic samples of the corresponding oil paints.

The characterisation by liquid chromatography of lake pigments prepared from European buckthorn (Rhamnus cathartica L.)

PurposeThe purpose of this paper is to prepare, analyse and measure the colour values of the lake pigments obtained from the reaction of Al3+, Fe2+ and Sn2+ metal salts with the natural dyes present in European buckthorn (Rhamnus cathartica L.).Design/methodology/approachA reversed‐phase high performance liquid chromatography (HPLC) with diode‐array detection method was utilised for the identification of buckthorn lake pigments. The extraction of dyes from the lake pigments was carried out with 37% hydrochloric acid/methanol/water (2:1:1; v/v/v) solution.FindingsAccording to the results of the HPLC analysis of the lake pigments, it was determined that rhamnetin, kaempferol, and emodin were present in the acid hydrolysed plant extract and in the lake pigment that was precipitated by Sn(II), quercetin‐3‐arabinosid, rhamnetin, and emodin were present in the non‐hydrolysed plant extract, and kaempferol, rhamnetin, isorhamnetin, and emodin were found in the lake pigment that was precipitated by Al(III). Rhamnetin and emodin were present in the lake pigment that was precipitated by Fe(II).Research limitations/implicationsIn the present context for the preparation of buckthorn lake pigments, a simple and practical method is presented. In addition, the analysis of the lake pigments was performed by reversed phase HPLC (RP‐HPLC) with diode array detector (DAD).Practical implicationsThe paper describes the preparation of lake pigments and their qualitative analysis. This method can be used to determine the origins of the dyestuffs used in historical art pieces.Originality/valueThe paper describes the development of methods for the analysis and the preparation of European buckthorn lake pigments.

A compact optical parametric oscillator Raman microscope for wavelength‐tunable multianalytic microanalysis

We have developed a high‐throughput microscope for wavelength‐tunable microscopic studies of materials by Raman, surface‐enhanced Raman, fluorescence, and reflectance spectroscopy. Narrow‐band excitation over a broad tuning range (410–2200 nm) is provided by a solid‐state, compact, and relatively inexpensive new class of diode‐pumped Nd:YAG optical parametric oscillator emitting approximately 1‐mJ, 10‐ns pulses at a rate up to 100 Hz. Rayleigh rejection over the tuning range is obtained with an array of angle‐tuned custom dielectric filters. Although high‐power, low duty‐cycle light sources have so far had only very limited use for tunable Raman and surface‐enhanced Raman spectroscopy, we show that undesirable nonlinear effects that arise from the high peak power of the output can be mitigated to produce good results with the proper choice of additional microscope elements. Measurements can be performed across the visible range with 20% sample‐to‐detector throughput and 10 cm−1 resolution. The system is also fitted with a fiber optic imaging system to perform fluorescence and reflectance spectroscopy measurements with a spatial resolution of 5 µm. We demonstrate the instrument's analytical capabilities by recording resonance Raman and surface‐enhanced Raman emissions from a commercial lake pigment and crystal violet, respectively, colorants of interest in cultural heritage studies and forensic science. We also isolate and measure the reflectance spectrum of a commercial lake pigment and the ultraviolet fluorescence spectrum of a single fiber of cochineal‐dyed silk. The tunability, flexibility, compactness, and spatial resolution of the device provide novel capability for multianalytic materials research in fields such as forensic science and cultural heritage studies. Copyright © 2012 John Wiley & Sons, Ltd.

Sample Treatment Considerations in the Analysis of Organic Colorants by Surface-Enhanced Raman Scattering

The introduction of surface-enhanced Raman spectroscopy (SERS) in the field of cultural heritage has significantly improved the analysis of the organic dyes and their complexes that have been used as textile dyes and pigments in paintings and other polychrome works of art since antiquity. Over the last five years, a number of different procedures have been developed by various research groups. In this Article, we evaluate the effect of pretreating samples by exposing them to hydrofluoric acid (HF) vapor prior to SERS analysis, a step designed to hydrolyze the dye-metal complexes and increase analyte adsorption on the nanosized metallic support, thus enhancing the SERS signal. Materials studied include pure colorants, commercial lake pigments, and fibers from dyed textiles, as well as actual aged samples, such as microscopic fragments of lakes on paper and ancient pigments and glazes from several works of art, covering a wide range of time, from the second century B.C. to the early 20th century. In each case, SERS spectra obtained with or without HF hydrolysis were critically evaluated. The pretreatment with HF vapor resulted in faster analysis and increased sensitivity in most cases, with the exception of dyed silk fibers, where silk protein hydrolyzates were found to interfere with SERS analysis. As a final point, a two-step procedure including SERS on untreated and treated samples is proposed as a standard approach: by analyzing a sample first without hydrolysis, and then, following removal of the colloid, upon HF treatment, the best and most reliable results for a great number of dyes and substrates are assured.

IDENTIFICATION BY RP-HPLC-DAD OF NATURAL DYESTUFFS FROM LAKE PIGMENTS PREPARED WITH A MIXTURE OF WELD AND DYER'S OAK DYE PLANTS

The lake pigments by means of the weld (Reseda luteola) and dyer's oak (Quercus infectoria) dye plants were prepared by using KAl(SO4)2 · 12H2O (alum), FeSO4 · 7H2O and SnCl2 · 2H2O mordants. A reversed-phase high performance liquid chromatography (RP-HPLC) with diode array detection (DAD) method was utilized for the identification of dyestuffs present in the lake pigments. The dyestuff extractions from the pigments were carried out with a solution mixture of 37% HCl:MeOH:H2O (2:1:1, v/v/v). The performed method is able to analyze and detect natural dyestuffs such as luteolin, apigenin, gallic acid, and ellagic acid present in the lake pigments.

Lithol Red: A Systematic Structural Study on Salts of a Sulfonated Azo Pigment

The first systematic series of single-crystal diffraction structures of azo lake pigments is presented (Lithol Red with cations=Mg(II), Ca(II), Sr(II), Ba(II), Na(I) and Cd(II)) and includes the only known structures of non-Ca examples of these pigments. It is shown that these commercially and culturally important species show structural behaviour that can be predicted from a database of structures of related sulfonated azo dyes, a database that was specifically constructed for this purpose. Examples of the successful structural predictions from the prior understanding of the model compounds are that 1) the Mg salt is a solvent-separated ion pair, whereas the heavier alkaline-earth elements Ca, Sr and Ba form contact ion pairs, namely, low-dimensional coordination complexes; 2) all of the Lithol Red anions exist as the hydrazone tautomer and have planar geometries; and 3) the commonly observed packing mode of alternating inorganic layers and organic bilayers is as expected for an ortho-sulfonated azo species with a planar anion geometry. However, the literature database of dye structures has no predictive use for organic solvate structures, such as that of the observed Na Lithol Red DMF solvate. Interestingly, the Cd salt is isostructural with the Mg salt and not with the Ca salt. It is also observed that linked eight-membered [MOSO](2) rings are the basic coordination motif for all of the known structures of Ca, Sr and Ba salts of sulfonated azo pigments in which competing carboxylate groups are absent.

Wybrane rodzaje żółtych, brązowychi czerwonych laków organicznych– wstępna metodyka badawcza

The article presents the results of research into properties of paints, basedon the selected yellow, brown and red organic lake pigments, including theirgranulation, opacity and colour in visible light, ultraviolet and coloured infrared.Paints were applied onto panels with monochrome groundings, made based onthe pigments that were historically used for this purpose. In order to illustratethe differences in the properties of lakes resulting from the use of differentsubstrates, a juxtaposition of photographs has been made, as well as a detaileddescription of the coloured products, obtained from the following raw materials:Aloe arborescens Mill., Reseda luteola L., Rubia L. tinctorum. The results have beenarranged in tables, including, additionally, a comparative list of photographs ofglazes, having similar fluorescence in the UV, and a similar tone in colour infrared.

Nondestructive Identification of Natural and Synthetic Organic Colorants in Works of Art by Surface Enhanced Raman Scattering

We present a new method based on surface-enhanced Raman scattering (SERS) for the nondestructive identification of organic colorants in objects whose value or function precludes sampling, such as drawings, prints, historic and archeological textiles, handwritten or printed documents, and forensic evidence. A bead of a polymer hydrogel loaded with a solution containing water, an organic solvent, and a chelating agent is used to extract minimal amounts of the colorants from the work of art for SERS analysis. Using a gel as a medium for the solvent mixture confines its action only to the areas of the work of art covered by the gel bead. The gel bead is then removed from the work of art, covered with a drop of Ag colloid, and examined with a Raman microscope. Transfer of the dye from the substrate to the gel does not require removing a sample from the work of art, therefore preserving the physical integrity of the object. Spectrophotometric color measurements confirm that color change is below the limit perceivable by a human observer. Finally, the size of the polymer bead can be reduced to a fraction of a millimeter in order to further minimize any impact on the work of art, without detriment to the effectiveness of the method. The technique has been successfully used for the analysis of a mordant dye on the 15th century Netherlandish tapestry, "The Hunt for the Unicorn", and of a synthetic lake pigment on a Meiji period Japanese woodblock print.

The opacity of tablet film coatings.

The opacity of tablet film coatings containing a variety of pigments and fillers has been assessed using a contrast ratio defined as the ratio of the measured reflectance of the incident light when the film is placed on a black substrate to the measured reflectance of the incident light when the film is placed on a white substrate. Films pigmented with calcium carbonate, calcium sulphate or talc had very low contrast ratios and only the inclusion of titanium dioxide imparted opacity. Films pigmented with the coloured lake pigments had contrast ratios dependent on both the parent dye and the dye concentration with the contrast ratios decreasing blue greater than red greater than orange greater than yellow. Films pigmented with the synthetic iron oxides all had very high contrast ratios. The results are consistent with the known theories of light scattering and absorption and illustrate the potential of this accurate, rapid and simple technique in the optimization of film formulations during product development.

Qualitative HPLC determination of main anthraquinone and lake pigment contents from Dactylopius coccus dye insect

0009-3130/11/4701-0103 2011 Springer Science+Business Media, Inc. 1) Department of Chemistry, Faculty of Science and Letters, Marmara University, 34722, Goztepe, Kadikoy, Istanbul, Turkey, fax: +90 (216) 336 74 68, e-mail: ozan.deveoglu@marmara.edu.tr; 2) Laboratory for Natural Dyes, Faculty of Fine Arts, Marmara University, 34718, Acibadem, Kadikoy, Istanbul, Turkey, e-mail: rkaradag@marmara.edu.tr; 3) Department of Pharmaceutical Toxicology, Faculty of Pharmacy, Marmara University, 34668, Haydarpasa, Istanbul, Turkey, e-mail: tyurdun@marmara.edu.tr. Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 92–93, January–February, 2011. Original article submitted July 24, 2009. Chemistry of Natural Compounds, Vol. 47, No. 1, March, 2011 [Russian original No. 1, January–February, 2011]