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The identification of colorants in historic plastics is a methodological and analytical challenge. Although deformulation is performed by the plastics industry, in the case of historical objects, sampling is often impossible, and in situ protocols are needed. The accurate identification of colorants provides insights into historical plastic formulations, supports planning of conservation studies, and critical data for objects that already exhibit color change (e.g. fading). Indeed, colorants may degrade following exposure to light, and color changes have been reported for plastic objects. The analysis of colorants remains a challenge, and microsampling is usually required. Successful identification of red pigments from thirty historical plastics is reported following a new in situ analytical protocol based on Raman microscopy. Information about other pigments, fillers and plastic polymers are reported. Fading has been observed in the historical plastic objects containing Pigment Red 53.

Several studies have suggested that shell colour may be phylogenetically distributed within the phylum Mollusca, but this pattern is confounded by our ignorance of the homology of colour and lack of understanding about the identity of most molluscan pigments. We use resonance Raman spectroscopy to address this problem by examining bivalve pigments producing a range of colours and compare spectra from taxa at different phylogenetic levels. The spectra of most shell pigments exhibited a skeletal signature typical of partially methylated polyenes, possibly modified carotenoids, with the strongest peaks occurring between 1,501–1,540 cm−1 and 1,117–1,144 cm−1 due to the C═C (ν1) and C–C (ν2) stretching modes, respectively. Neither pigment class nor mineral structure differentiated Imparidentia and Pteriomorphia. Spectral acquisitions for purple pigments for two species of Asaphis suggest that identical or nearly identical pigments are shared within this genus, and some red pigments from distantly related species have similar spectra. Conversely, two species with brown shells have distinctly different pigments, highlighting the difficulty in determining the homology of colour even within a single class of pigments. Curiously, we were unable to detect any Raman activity for green‐coloured shell or pigment peaks for the yellow area of Codakia paytenorum, suggesting that these colours are due to structural elements or a pigment that is quite different from those observed in other taxa examined to date. Our results are consistent with the idea that classes of pigments are evolutionarily ancient but heritable modifications may be specific to clades.

Smudging is one of the most serious damages of Mogao Grottoes' murals. In this paper, confocal micro-Raman spectroscopy is adopted to investigate the smoked murals in Mogao Grottoes. The exutive fragments from the smoked murals in 71 Grotto have been analyzed. The white pigment, which is covered by a layer of black, is identified as calcite, and the black is amorphous carbon. No any other chromatic pigments were found in all exutive fragments. From which, we may speculate that the white pigment (CaCO3) is stable undergoing smoking and other chromatic pigments may have been destroyed by smoking. Based on the analysis and the records of the Mogao Grottoes' murals, a representative smoking process was designed to explore the degradation of the pigments in an imitative mural. The typical pigments, including white (aragonite), black (carbon) and red (vermilion), are analyzed from imitated smoked mural, and the results show that aragonite is stable and vermilion is damaged. It is judged that the vermilion has been destroyed by the smoking process, in which the high-temperature smoke makes the vermilion easily react with oxygen and produce the mercury vapor and sulfur dioxide. The simulative smoking experiment is reliable and feasible for investigating the degradation process of pigments and is proposed to investigate more pigments which can supply significant and important information for the restoration and conservation of smoked murals in Mogao Grottoes. Copyright © 2017 John Wiley & Sons, Ltd.

Red dyes in seven belts (trariwe) belonging to the Mapuche culture, dated as beginning of the XXth century and stored in Museo Regional de la Araucania, Chile, were studied by using ultraviolet-visible, liquid chromatography coupled to mass spectrometry, Raman and Surface Enhanced Raman Scattering spectroscopies. Red dyes were extracted and analysed; the spectral analysis allowed identifying that the principal red dye in five samples is highly consistent with a commercial synthetic aniline, the azopigment PR57. Another monoazopigment, an orange benzimidazolone, was identified in two samples. A molecular model for the PR57/Ag surface interaction supports the idea that the dye mainly exposes to the metal the carboxylate and sulphonate groups; the red azopigment is oriented rather tilted with the two aromatic rings being almost coplanar to the surface. The electrostatic interactions are the main factor of the PR57/Ag layer interaction. Copyright © 2017 John Wiley & Sons, Ltd.

Microbial communities composed by eukaryotic microorganisms: melanized fungi and algae colonizing the interior of gypsum crusts in hyperarid zone of the Atacama desert were studied by Raman microspectroscopy. Melanin pigments present in fungi cell walls were identified directly in the colonized gypsum crust and on the cultivated culture of the fungi from Neocatenulostroma genus. Two signature broad bands located at wavenumbers 1605–1580 cm −1 and around 1350 cm −1 have been detected and confirmed melanin as a main fungal protective pigment.

In this work, we present a complete Raman investigation of a class of compounds that has not received great attention yet, the red naphthol-based azo dyes. We selected a group of red azo dyes often used by artists in inks and lake pigments: acid red 1, acid red 14, acid red 18, acid red 26, acid red 27, and acid red 73. A set of reference materials was studied by dispersive Raman, FT-Raman, and surface-enhanced Raman spectroscopy. The reference spectra were used in the study of late 19th century Japanese polychrome woodblock prints. The azo dyes selected for this study generally gave good Raman spectra at all excitation wavelengths. The results obtained by the various Raman techniques are compared, and the main difficulties in the identification of the compounds in works of art are illustrated and discussed. The fluorescence coming from the matrix in which the colorants are embedded can obscure their Raman signal. For this reason, the advantages and drawbacks of surface-enhanced Raman spectroscopy with non-sampling extraction of the colorants have been evaluated. Copyright © 2017 John Wiley & Sons, Ltd.

The introduction of synthetic dyes and pigments into commerce in the late 19th century was a stimulating time for experimental scientists in their laboratory formulations and for artists in their usage. Nowadays, the period of pioneering syntheses and employment of synthetic organic colouring materials is highly intriguing for scientific research and for conservation purposes in heritage science. In this work, a combination of spectroscopic and chromatographic methods has permitted the elucidation of the chemical composition of 16 early synthetic organic pigment powders from the Lefranc experimental laboratory collection dating 1890–1914. It can be hypothesized that the most successful of these formulations could have been finalized in paint tubes and released onto the market, meaning that they may even be found in artworks from the same period. Specifically, information from this crucial period of transition from the exclusive use of natural dyes/colourants (such as neoflavonoids and plant and insect anthraquinones) to the introduction of their synthetic counterparts (such as synthetic alizarin and purpurin, and acid stable cochineal, together with monoazo and diazo pigments) is confirmed through Raman/surface-enhanced Raman spectroscopy and high-performance liquid chromatography with diode array detection. By means of X-ray fluorescence and mid-Fourier transform infrared spectroscopy, a combination of traditional and modern inorganic substrates has been identified (alum, kaolin, barium sulfate and metallic salts), while Raman has provided additional data regarding the possible complexation of these pigments in the form of lakes. Copyright © 2016 John Wiley & Sons, Ltd.

Raman spectroscopy combined with synchrotron radiation-based techniques and electron microprobe was used to study the yellow component of slips of marbled sigillata. Electron microprobe analysis emphasized on a significant corpus that the yellow component was well made from a titanium-rich clay preparation while X-ray absorption near edge structure investigation at Ti K-edge confirmed the massive presence of pseudobrookite (Fe2TiO5) in good agreement with previous study. Raman spectroscopy was correlated with X-ray absorption near edge structure results in order to extract the Raman spectra of pseudobrookite, which was compared with these ones of synthesized pseudobrookite powder reference. The investigation of a significant corpus (43 sherds) of marbled sigillata revealed that all samples exhibited similar Raman spectra in yellow zones attributable to the pseudobrookite structure. However, all spectra show the same features compared with the spectra of reference powder, that is, peak shifts and line broadenings, which could be related to Mg and/or Al substitutions in pseudobrookite crystals of marbled sigillata. The substitution plays a dual role in pseudobrookite structure: (1) stabilizes the structure through involving an increase of cationic disorder and (2) makes the color less dark and yellow, which could account for the nice yellow color of marbled sigillata. Copyright © 2016 John Wiley & Sons, Ltd.

Raman spectroscopy was employed to investigate six Imperial China Engraved Coiling Dragon stamps non-destructively. The results have shown that (1) the main colors (yellow, green, scarlet, brown, vermilion, and blue) on the six stamps were all prepared from inorganic pigments, including chrome yellow, chrome orange, Prussian blue, red lead, magnesium sulfate hydrate, and ultramarine blue. (2) Raman spectrometer has been allowed for successfully identifying the molecular structure of the pigments printed on the six examined stamps, suggesting that such a dual analytical approach could satisfy the need for pigment identification on stamps. (3) The finding that certain pigments were intentionally mixed to produce a whole different hue or color, the mechanism of which could be explained by theories of chromatology and metamerism, also provides new insight into the future conservation, authentication, and restoration of the early printings. Copyright © 2015 John Wiley & Sons, Ltd.

Madder has been used as a textile dye and pigment in works of art since antiquity. Madder dyes from different botanical species are characterized by different series of anthraquinone derivatives. The occurrence of one or more of these compounds in various relative amounts may provide a useful indication of the plant species used to obtain the dye. In this work, surface-enhanced Raman spectroscopy (SERS) was applied to the analysis of textile fibers dyed with madder from two different botanical species, Oldenlandia umbellata L. and Rubia tinctorum L. The resulting SERS spectra were interpreted in light of the actual composition of the madder dyes as determined by high-performance liquid chromatography. Interestingly, the SERS spectra were found to exhibit very distinctive spectral features depending on the different anthraquinone derivatives present in the dyes. In particular, the SERS spectrum of O. umbellata L. was found to match the spectrum of alizarin, while the SERS spectrum of R. tinctorum L. was surprisingly dominated by signals due to the less studied anthraquinone compound pseudopurpurin. With this study, we demonstrate that SERS spectra may offer valuable information regarding the major coloring constituents present in different madder species. Moreover, our work shows that not only can SERS be used successfully to differentiate among closely related anthraquinone derivatives, but also that this technique is particularly suitable for the detection of pseudopurpurin, leading to the identification of this compound in a number of works of art. Copyright © 2015 John Wiley & Sons, Ltd.

In this investigation the chemistry of the lichens Gondwania regalis, Teloschistes exilis and Xanthoria candelaria (Teloschistaceae) have been recorded by means of Raman spectroscopy. The non-destructive analysis provided the recognition of parietin and conjugated polyenes, probably belonging to the carotenoid family for all the investigated specimens. Bands at ca. 1370 and 1600 cm−1, respectively, assigned to the ν(C―O) and ν(CO) modes of the phenyl group of the anthraquinone compound, as well the bands at ca. 1005, 1158 and 1527 cm−1, possibly assigned to the β-carotene in the FT-Raman spectra, have provided valuable spectroscopy data for the identification of the biomarkers for these lichen pigments. Thus, this is the first report of parietin and carotenoid in T. exilis and X. candelaria tissues even as the parietin anthraquinone for G. regalis tissues, which are effective pigments against free radicals from UV radiation. Copyright © 2014 John Wiley & Sons, Ltd.

This paper investigates, using only Raman spectroscopy, the spectral differences among the synthetic ultramarine blue (J. B. Guimet) and three natural ultramarine blues (lazurites) corresponding to three lapis lazulis from different geographical sources (Chile, Afghanistan and Siberia). The synthetic ultramarine blue used as reference pigment is the identified in an artwork created around 1917 by the Catalonian modernist painter Ramon Casas i Carbo. This synthetic pigment is compared with the three natural ultramarine blues and, in his turn, the latter are also compared each other. In order to quantify the spectral differences, a rigorous methodology based on the Euclidean distance between homologue spectral segments (or intervals) has been developed and presented here. Copyright © 2014 John Wiley & Sons, Ltd.

The natural sepia pigment is based on eumelanin, the most prevalent type of melanin, and can be obtained from the ink sac of different members of the Cephalopoda class, such as cuttlefish and squid. The main components of natural sepia are indole derivatives, but pigments prepared following historical recipes are generally more heterogeneous as they may also contain proteins, polysaccharides, and lipids. Sepia is difficult to identify in works of art owing to its heterogeneity, insolubility in most organic solvents, interference by the binding media, and its poorly defined spectroscopic properties. In the present study, three commercial natural sepia pigments, along with a sample extracted from cuttlefish following a historical recipe in an artists' manual, a relatively more pure commercial melanin, and a synthetic eumelanin obtained by the oxidation of dopamine were characterized by normal Raman and surface-enhanced Raman scattering (SERS), complemented by Fourier transform infrared, pyrolysis–gas chromatography–mass spectrometry, and X-ray fluorescence, in order to obtain vibrational signatures for the identification of the pigment in works of art. Pyrolysis–gas chromatography–mass spectrometry and X-ray fluorescence analysis showed that the pigment composition is strongly influenced by the extraction procedure used. Lipids were identified in the chromatograms of all the natural samples analyzed, and the majority of these also showed the presence of cholesterol derivatives. Additional components resulting from the decomposition of polysaccharides were found to be present in the sepia extracted from cuttlefish in our laboratories. Normal Raman and SERS were also used to study two sepia inks applied on paper and subjected to accelerated aging. In the SERS measurements, a hydroxylamine-reduced silver colloid was used as this substrate is suitable for the identification of other natural heterogeneous black-brown pigments. The SERS methodology developed was applied to identify sepia in Waiting for Aaron, a drawing by the 19th century artist Robert Frederick Blum. Copyright © 2014 John Wiley & Sons, Ltd.

The presented study describes the deterioration of a traditional pigment, malachite—[Cu2(CO3)(OH)2] in different binders, as a consequence of environmental effects acting on paint layers which were prepared according to traditional Baroque recipes. Malachite has often been reported to be very permanent in all binding media; however, investigations of aged and non-aged paint layers by means of Raman microscopy have shown instability of the carbonate part of the molecule, especially when malachite is present in an egg yolk medium. Decomposition of the pigment and the formation of degradation products such as copper oxide (tenorite—CuO) were observed. The possible formation of another copper oxide, paramelaconite—Cu4O3 was also taken into consideration. In order to obtain additional information on the degradation processes which affect malachite paint layers, supporting analytical methods, such as scanning electron microscopy and X-ray diffraction, were used. Copyright © 2014 John Wiley & Sons, Ltd.

Direct identification of pigments in mediaeval illuminated manuscripts was one of the first applications of Raman spectroscopy in art and archaeology. In previous in situ analysis of handwritings, the equipment was typically provided with a single excitation source. In this work, a portable Raman spectrometer (EZRAMAN-I-DUAL Raman system) is introduced to characterise the pigments used in an important illuminated mediaeval manuscript, De Civitate Dei (Library in Bruges, Ms.106). Characteristics important for these in situ measurements were discussed. We introduce a set-up that allows stable positioning of the equipment and point out the advantage of the availability of two lasers, which are part of the instrument. Good performance of the introduced Raman spectrometer, to allow pigment identification in a short time, is proved. Finally, pigments such as lead white (2PbCO3 · Pb(OH)2), lead–tin yellow type I (Pb2SnO4), malachite (Cu2CO3(OH)2), mosaic gold (SnS2), vermillion (HgS), carbon black (C), red lead (Pb3O4) and azurite (Cu3(CO3)2(OH)2) could be identified. These pigments were often used in mediaeval artworks and contribute to the enrichment of information of the materials used by the illuminator. Copyright © 2014 John Wiley & Sons, Ltd.

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.

The development of solid-state chemistry at the end of the 19th century offered a variety of routes to colour a glass matrix. Eight enamelled glass objects made by Philippe-Joseph Brocard and two representative objects made by Emile Galle have been analysed using a mobile Raman instrument at the Musee des arts decoratifs (Paris) in order to compare their colouration technology. White, blue, yellow, green, orange, red, brown and black pigments have been identified. If most of the pigment palette is common to both craftsmen and typical of the second half of the 19th century, innovative uses are recognized for Galle (wollastonite as an opacifier, manganese oxides in black mixtures) and Brocard (specific black and grey, pigment mixture, shade modification by small addition of white and red pigments). This preliminary work confirms the potential of Raman spectroscopy, not as a simple analytical method but as a way to document the ancient technology of fine art objects and to discriminate between different genuine productions and/or copies. Copyright © 2014 John Wiley & Sons, Ltd.

Micro-Raman spectroscopy has been used on adult bivalve shells to investigate organic and inorganic shell components but has not yet been applied to bivalve larvae. It is known that the organic matrix of larval shells contains pigments, but less is known about the presence or source of these molecules in larvae. We investigated Raman spectra of seven species of bivalve larvae to assess the types of pigments present in shells of each species and how the ratio of inorganic : organic material changes in a dorso-ventral direction. In laboratory experiments, we reared larvae of three clam species in waters containing different organic signatures to determine if larvae incorporated compounds from source waters into their shells. We found differences in spectra and pigments between most species but found less intraspecific differences. A neural network classifier for Raman spectra classified five out of seven species with greater than 85% accuracy. There were slight differences between the amount and type of pigment present along the shell, with the prodissoconch I and shell margin areas being the most variable. Raman spectra of 1-day-old larvae were found to be differentiable when larvae were reared in waters with different organic signatures. With micro-Raman spectroscopy, it may be possible to identify some unknown species in the wild and trace their natal origins, which could enhance identification accuracy of bivalve larvae and ultimately aid management and restoration efforts. Copyright © 2014 John Wiley & Sons, Ltd.

Copper resinate is a green pigment widely used by the 16th century painters, as many surveys on Italian and European paintings proved. The pigment is a transparent green glaze, and its color is due to copper salts of resin acids. The oldest recipes suggest the preparation of copper resinate by mixing verdigris with terpenic resins as Venice turpentine (conifer resins) on hot ashes. The detection of copper resinate in paintings is up to this time an analytical challenge. We examined the Raman features of copper resinate (powder and in a mock paint film with linseed oil) and compared them with verdigris. Six laser sources (488, 514, 532, 633, 785, and 830 nm) were used in different laboratories to highlight the drawbacks and advantages of a specific excitation source. The obtained results were applied in the analyses of a famous Caravaggio's painting. For a detailed interpretation and full exploitation of the Raman spectra, Fourier transform infrared spectroscopy measurements were carried out as well. Copyright © 2014 John Wiley & Sons, Ltd.

This work presents the results of the study of plasterwork decorations located on the stalactite vaults of the Hall of the Kings in the Alhambra (Granada, Spain) by means of Raman micro-spectroscopy. Field investigations were carried out in situ using a portable Raman spectrometer during a conservation campaign in a completely non-invasive manner. In addition, taking into account the results obtained, a well-directed sampling was carried out to obtain complementary information by means of laboratory studies. Despite several practical problems during the non-invasive field studies (like difficulties for probe positioning and vibrations of the scaffolding), almost all the pigments present in the decorations of the Hall were identified using excitation at 785 nm: cinnabar, minium, carbon black, natural lapis lazuli and synthetic ultramarine blue. In addition, evidence of different degradation mechanisms of the red pigments was obtained in situ. On the contrary, the identification of blue-greenish and green pigments had to be performed on microsamples using a Raman microscope with excitation at 514 nm in the laboratory. In samples with blue and green areas, azurite severely degraded to clinoatacamite was identified. These were probably the remains of the oldest blue decorations. In addition, a technique for green decorations consisting on copper chlorides mixed with a small amount of lapis lazuli was identified. Other degradation products, identified in the laboratory regardless of the color of the pigment, were calcium oxalates. Finally, the laboratory studies also enabled the investigation of the stratigraphy of the pictorial layers. In this way, the presence of re-decorations with overlaying layers of pigments even of different colors was revealed. Copyright © 2014 John Wiley & Sons, Ltd.

Herzberg staining, a quick and convenient tool for distinguishing non-wood fibers from wood pulp, and Raman spectroscopy were employed to investigate three paper currencies issued under the reign of the Chinese Ming and Qing Emperors between 15th and 19th centuries - da ming bao chao (AMS C-14 Date: 1410-1435 AD, ±1σ) from the Early Ming Dynasty (1405–1433 AD) and da qing bao chao (1859 AD) and hu bu guan piao (1854–1858 AD) from the Late Qing Dynasty (1840–1911 AD). Fiber staining and microscopic examination revealed a predominance of bast fiber from probably mulberry trees and very few cotton fibers (supposed to be environment contamination) in da ming bao chao; fibers in da qing bao chao and hu bu guan piao turned out to be quite pure, which are also bast fibers but very likely came from ramie and paper mulberry trees, respectively. Raman analysis of red, blue, and black pigments on the investigated paper currencies showed that: (1) The reddish seal on da ming bao chao is not a vermilion (HgS) paste, as it is traditionally assumed, but instead a red lead (or minium, Pb3O4) one. The red pigments on both da qing bao chao and hu bu guan piao are vermilion (HgS). (2) Prussian blue (Fe7(CN)18⋅14-16H2O), a Western pigment, was identified as blue on both da qing bao chao and hu bu guan piao. (3) The black pigment on all these three paper currencies is amorphous carbon from soot. (4) Raman analysis of evenly distributed white pigment particles among the fibers in da qing bao chao confirmed the use of calcium carbonate (CaCO3) as coating pigment or fillers. Both microscopic examination of stained fibers and Raman analysis allowed, for the first time, the understanding of fiber and pigment use in producing ancient Chinese paper currencies. Copyright © 2013 John Wiley & Sons, Ltd.

Polyenic pigments in octocorals have been investigated by Raman spectroscopy using laser excitation at 532, 785 and 1064 nm. The spectral features suggest the structural nature of carotenoids from Phyllogorgia dilatata, Leptogorgia punicea, Muricea atlantica, Carijoa riisei and conjugated polyenals from L. punicea, L. setacea, Muricea flamma and Renilla muelleri. The observed vibrational bands at ca. 1540–1520 ν1(C=C), 1159 ν2(C–C) and 1005 cm−1 ρ3(C–CH3) were assigned to carotenoids, whereas the identification of non-methylated conjugated polyenals have been proposed due to two major Raman bands at ca. 1500 and 1120 cm-1, assigned to ν(C=C) and ν(C–C), respectively. Copyright © 2012 John Wiley & Sons, Ltd.

In an art historical context, pigments identification is exceedingly important for the conservation, interpretation and preservation of art works. In practice, the pigments may have been used in mixtures (or in admixtures) with other pigments to produce special effects or tonal qualities. Binary mixtures are the more frequently mixtures used in paintings; for instance, it is commonly used the mixture of a yellow pigment with a blue pigment to produce green colors. In this situation, the pigments identification is actually done on Raman spectra of pigment mixtures and may turn out to be a complex and tedious task, especially when analyzing spectra with a large number of bands located close together as it is the case of mixtures of synthetic organic pigments. To decrease complexity whilst also speeding up the identification process, a system to automatically identify Raman spectra of binary mixtures of pigments is presented in this work. The system is able to identify the two different pigments in the mixture from spectroscopic signature obtained by Raman spectroscopy. The technique has been proved with mixtures showing its robustness against some of the critical factors that could affect the application of Raman spectroscopy for pigments identification as distortion and wavenumber shifts in key Raman bands due to different measurement environmental conditions. The results led to conclude that the system could be a useful tool to help the analyst to make a decision. Copyright © 2012 John Wiley & Sons, Ltd.

On-site Raman spectroscopy is used to investigate four mosque lamps and a bottle dating back to the 13–14th centuries (Syria and/or Egypt, Mamluk period) from the Department of Islamic Art, Musee du Louvre, Paris. The pigments and the enamelled glass matrix have been identified in order to discuss their technology. A comparison is made with one masterpiece from the 19th century made by Brocard. The results obtained for blue (lapis lazuli or Co-coloured glass), yellow (Naples yellows or zinc/chrome yellow), green (mixture of the aforementioned blue and yellow pigments or lead chromate for restorated foot) red (hematite), white (cassiterite or arsenate) and pink (hematite and cassiterite) pigments are presented. The consistency of the pigments period of use/technology with the datation proposed for each artefact is evaluated. For one lamp, the detection of quartz in some places of the hematite-rich glassy layer supporting the gold is related to the search of a physical bonding with the artefact body. Carbon residues in such enamel are consistent with the use of an organic medium to place the enamel powder before the firing. Copyright © 2012 John Wiley & Sons, Ltd.

The colour palette from two 20th century and one 21st century Indonesian paintings from the island of Bali was determined by Raman microscopy. There is very little information concerning the artistic techniques from this region of the world and the influences in materials introduced by western artists. The most interesting finding of our study was the increasing substitution of natural pigments by modern synthetic organic pigments. The findings were also compared with samples of representative pigments commonly used by Bali artists, donated by a renowned Balinese painter. Raman microscopy, combined with Fourier transform infrared spectroscopy, high-performance liquid chromatography and μ-EDXRF, was able to separate the different components on several colours, and to identify both synthetic organic pigments and inorganic components. Three azo pigments from the diarylide subclass, PY 83, PY 55 and PO 16, were identified on the yellow, brown, red and orange colours. A copper phthalocyanine blue PB 15:x and a basic dye BB 26 were responsible for the blue colours, the former admixed with ultramarine blue. Goethite was sometimes introduced to create the green colour. Two other basic dyes, BY2 and PG 4, were the main chromophores of the yellow and green samples of local pigments. The inorganic pigments comprised bone white, bone black, carbon-based black pigment, haematite, goethite, vermilion, ultramarine blue and anatase. Finally, the ground layer of all the paintings was identified as rice starch, with a double function of a white pigment. Copyright © 2012 John Wiley & Sons, Ltd.

Phyllogorgia dilatata is a Brazilian endemic gorgonian with a natural color ranging from white to pale yellow. An unusual violet pigmentation has been observed in colonies with tissue damage and skeleton anomalies. In order to investigate the chemical composition of these pigments, we have used in situ Raman spectroscopy to characterize the white/cream and violet tissues as well as sclerites, a skeletal component consisting of calcite, from both samples. Violet/purple pigmentation surrounding tissue necrosis is characterized as purpling, in response to fungus infection and allelopathic interactions. The spectroscopic analysis of the white-cream tissues, designated as healthy, has revealed the presence of the carotenoid peridinin, typical of the endosymbiont that harbors this species; however, peridinin was not observed in the colorless sclerites analysis, presenting bands exclusively of calcite. In contrast, the violet coloration of damaged tissue has also been observed in the sclerites. Both showed Raman bands corresponding to unmethylated polyunsaturated aldehyde, besides calcite bands. This is the first report of purpling in a Brazilian octocoral, identified as a derivative of the biochromes named psittacofulvins, which have been reported as exclusive in parrots. Copyright © 2011 John Wiley & Sons, Ltd.

This work seeks to identify the slight changes in the characteristic CH stretching region (3100–2800 cm−1) of a protein-based binder and fatty acid esters from egg yolk, which may occur in complex paint samples due to the presence of particular pigments. To date, this protein region—where historic pigments do not show characteristic Raman bands—has not been used to identify possible interactions between painting materials, in spite of its potential due to the mentioned feature. This study is based on the investigation of pure egg yolk model samples and tempera model samples prepared by mixing this binder with some historic pigments (cinnabar, raw Sienna, lead white, gypsum, calcite, azurite, lapis lazuli and smalt) as binary samples. All samples were analyzed in this region by Raman microscopy (RM) coupled with principal component analysis (PCA) for three color groups (red, white and blue) separately. The results show relevant spectral changes in the CH stretching region of amino acids and polyunsaturated fatty acids esters of the egg yolk binder, particularly in the azurite, lead white and gypsum-based tempera samples. Lesser interactions were discerned in the tempera samples made with smalt, as well as shift in the region of polyunsaturated fatty acid esters of the egg yolk binder in the cinnabar and raw Sienna-based tempera paintings. No interactions were recognized between the egg yolk and the pigments calcite and lapis lazuli. The effectiveness of applying RM combined with PCA for identifying interaction processes between binders and pigments is demonstrated. Copyright © 2011 John Wiley & Sons, Ltd.

The nature of the pigments in octocorals has been investigated by Raman spectroscopy, where laser excitation at 632.8 and 1064 nm were used to characterize the colored components present in the skeleton of the exotic pink-yellow soft coral Chromonephthea braziliensis, the reddish purple sea fan Leptogorgia punicea and the endemic deep violet red Leptogorgia violacea from the southeastern coast of Brazil. The observed positions of two major Raman bands at ca 1500 cm−1 [ν(CC)] and 1130 [ν(CC)] for all specimens strongly suggest the presence of a mixtureof conjugated polyenes belonging to a class of compounds named parrodienes. The hemiketal steroidal feeding deterrent, 23-keto-cladiellin-A, isolated from C. braziliensis was identified in the crude extracts by the Raman analysis using 1064 nm excitation. The observation of the most important vibrational bands of this compound can be useful in future investigations to monitor its presence in crude extracts of C. braziliensis and or other species. Copyright © 2010 John Wiley & Sons, Ltd.

Shrines (or altars) are constructed in China for worshiping ancestors, Bodhisattva, and God of Wealth. In this work, pigments from the shrine of Kaiping Diaolou tower were analyzed by micro-Raman spectroscopy, in conjunction with other analytical methods including scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) and X-ray fluorescence (XRF). Paintings of the shrine were composed of 2–3 pigment layers and the total thickness was determined as about 200–300 µm by optical microscopy and SEM, indicating the fine painting skills applied in the construction of the shrine. The green pigments on the surface layer of the green fragment were identified as a mixture of lead phthalocyanine (PbPc) and cornwallite (Cu5(AsO4)2(OH)4) by XRF and micro-Raman spectroscopy with two different excitation wavelengths (488 and 785 nm). Underneath the green layer, red and yellow ochre were found. The pigments on the surface layer of red and blue fragments were identified as hematite (Fe2O3) and lazurite or synthetic ultramarine [(Na8(Al6Si6O24)S3)], respectively. Finally, the pigments under the two surface layers were identified by EDX and micro-Raman spectroscopy as chromium oxide (Cr2O3), gypsum (CaSO4·2H2O) and calcite (CaCO3). Copyright © 2011 John Wiley & Sons, Ltd.

Fourier Transform Raman spectroscopy (FT-Raman) has been applied for the non-destructive in-situ analysis of pigments on differently colored flower petals of pansy cultivars (Viola x wittrockiana). The main target of the present study was to investigate how far the Raman mapping technique through FT-Raman spectroscopy and cluster analysis of the Raman spectra is a potential method for the direct, in-situ discrimination of flavonoids (flavonols against anthocyanins) and of carotenoids occurring in flowers, using intact and differently colored flower petal of Viola x wittrockiana for this case study. In order to get more information about the reliability of the direct in-situ flavonoid detection by the Raman method, pigments extracts of the petals were separated by thin-layer chromatography (TLC) and investigated by Raman spectroscopy. Hierarchical cluster analysis (HCA) of the Raman spectra from reference pigments (carotenoids, anthocyanins and flavonols), from areas of the flower petals, and from the TLC extracts allowed discriminating the various pigments, in particular flavonoids (flavonols against anthocyanins) and carotenoids. With a two-dimensional Raman mapping technique, which provides a chemical image of the sample under investigation, we determined by cluster analysis the distribution of carotenoids, anthocyanins and flavonols from the outer layer of the petals, and by integrating through suitable spectral regions selected as characteristic markers for particular pigments their relative concentration could approximately be determined. We found a satisfactory correlation between the patterns seen on the visible images and the patterns on the chemical images obtained by Raman mapping. Copyright © 2011 John Wiley & Sons, Ltd.

The reproduction of an old recipe to obtain the pigment known as verdigris leads to a complex mixture of hydrated copper(II) acetates containing neutral verdigris and two varieties of basic verdigris. Since the characterization of such mixture is complicated by the lack of reference standards, we complemented our Raman measurements with Fourier transform infrared (FTIR) and X-ray diffraction (XRD) experiments to perform our analysis, which has been compared with available studies. The spectral analysis allowed us to distinguish the different verdigris varieties, with stretching and bending wavenumbers assigned to the following chemical groups: OH groups (OHhydroxy and OHH2O) (3600–3050 cm−1), CuO bonds (CuO and CuOH) (1000–450 cm−1) and those corresponding to the acetate group (CH3COO−), i.e. (CH3: 3000–2850 cm−1) and (COO−: 1600–1400 cm−1 and 700–600 cm−1). Both wavenumbers and Raman intensities were used to quantify the relative compositions of the mixture components. Copyright © 2010 John Wiley & Sons, Ltd.

Powdered pigments found in bowls from the Pompeii archaeological site and some wall-painting fragments from the Vesuvian area (conserved in the National Archaeological Museum of Naples) were investigated by microscopic Raman and FTIR spectroscopies, X-ray diffraction and scanning electron microscopy-energy dispersive X-ray. Brown, red and yellow pigments are common ochres based on goethite and haematite. The blue pigment is Egyptian blue: the presence of tridymite and cristobalite indicates firing temperatures in the 1000–1100 °C range. Pink pigments were prepared both with purely inorganic materials, by mixing haematite and Egyptian blue (violet hue), or presumably by adding an organic dye to an aluminium-silica matrix. A white powder found in a bowl is composed mainly of the unusual pigment huntite (CaMg3(CO3)4). Celadonite is found in the green samples from the wall paintings, together with Egyptian blue and basic lead carbonate, while the heterogeneous green pigment in a bowl shows malachite mixed with goethite, Egyptian blue, haematite, carbon, cerussite and quartz. Copyright © 2010 John Wiley & Sons, Ltd.

This work explores the application of principal component analysis (PCA) on first-derivative Raman spectra to investigate historical tempera paint model samples. Various paint model samples were prepared containing pure blue pigments (azurite, lapis lazuli and smalt), pure red pigments (cinnabar, minium and raw Sienna), pure white pigments (lead white, chalk and gypsum), pure egg yolk as binder and tempera model samples obtained by mixing each of the pigments with the binder, and further characterized by Raman spectroscopy. The corresponding Raman spectra were used to apply PCA in order to test whether spectral differences allowed discrimination of samples based on their composition. Multivariate analyses were performed separately on three data matrices, one for each color, namely, white, blue and red, corresponding to the model samples, and all containing the spectral data of the binder model sample. Different pretreatments, that is log and derivative spectra, were performed on the spectra since no pattern distributions were obtained when the original Raman spectra were analyzed. Nevertheless, the multivariate analysis of the original Raman spectra was able to track alterations of sensitive pigments due to laser interaction. Results showed the excellent ability of PCA, when applied to the derived Raman spectra, to discriminate model samples according to their differing compositions in the three groups of model samples tested. This is the first attempt to use this approach in the field of cultural heritage and demonstrates the potential benefits for identifying historical pigments and binders for purposes of conservation and restoration. Copyright © 2010 John Wiley & Sons, Ltd.

The mechanisms of red lead degradation were studied in a medieval Portuguese codex, LorvApocalypse (1189), by Raman microscopy (µ-Raman) and micro-X-ray diffraction (µ-XRD). The range of pigments found for the illuminations is mainly limited to vermilion, orpiment and red lead. Micro-Fourier transform infrared spectroscopy (µ-FTIR) determined that the pigments were applied in a proteinaceous binding medium. In the red and orange colours, arsenic (As) was determined, by micro-energy dispersive X-ray fluorescence (µ-EDXRF), to be ranging 1 - 4% (wt %). For those colours, lead white and calcium carbonate were found as fillers whereas orpiment was applied as a pure pigment. Raman microscopy identified, unequivocally, the degradation product of red lead as galena (lead (II) sulphide, PbS). To determine the main factors affecting red lead degradation, a set of accelerating ageing experiments was designed to assess the influence of extenders and of the two other pigments, vermilion and orpiment. The experiments were followed by µ-Raman, µ-EDXRF and XRD. Raman microscopy results for the simulation of degradation of red lead, in the presence of orpiment, are in agreement to what was found in the Lorv˜ ao Apocalypse, galena being the main degradation product; also in common is a Raman band at ca. 810 cm −1 , which was attributed to a lead arsenate compound. It was concluded that in Lorv˜ ao Apocalypse, the degradation of red lead was a result of its reaction with orpiment. Copyright c � 2009 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this article.

An attempt to explain the origin of the vivid red color in precious pink and red corals was undertaken. Raman and IR spectroscopies were applied to characterize white, pink and red corals. The position of the Raman signal near 1500 cm −1 of some corals and pearls was associated by several authors with the presence of the mixture of all-trans-polyenic pigments, containing 6 – 16 conjugated C C bonds or β-carotenoids. This hypothesis was examined theoretically by performing extensive B3LYP-DFT calculations of vibrational spectra of the model polyenic compounds. The B3LYP/6-311++G ∗∗ predicted positions of the dominating Raman mode depend on the number of C Cu nits (Cn parameter) and can be accurately predicted for larger systems from a simple nonlinear fit. The DFT-predicted Raman activities of these modes are extremely sensitive to Cn ,a nd sharply increase with the number of double bonds. This implies a presence of only – two to three polyenes differing slightly in the number of C C units as the source of color in pink and red corals. Copyright c � 2009 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this article.