Evaluation of Raman and SERS analytical protocols in the analysis of Cape Jasmine dye (Gardenia augusta L.)

The identification of organic colorants in works of art (such as dyes on textiles or organic pigments) by Raman spectroscopy is generally limited by the presence of a strong fluorescence background. In this paper, the effectiveness of minimizing fluorescence in the analysis of Cape Jasmine (Gardenia augusta L.) by dispersive Raman spectroscopy at three different excitation wavelengths (633, 785 and 1064 nm) and by surface‐enhanced Raman spectroscopy (SERS) with and without acid hydrolysis is evaluated and compared. It is shown that these vibrational techniques offer an alternative analytical approach, when, as is particularly the case of Cape Jasmine, sample preparation procedures that are routinely applied for natural organic dyes and pigments cause alterations that lead to low sensitivity in the more classical high‐performance liquid chromatography‐photodiode array (HPLC‐PDA) analytical protocols. Samples of the yellow dye G. augusta L. in the following forms were analyzed: dyed on alum mordanted wool, dyed on nonmordanted and alum mordanted silk, pigment precipitated on hydrated aluminum oxide, extract mixed with a protein binder and painted on glass, and as a water‐based glaze applied on a mock‐up of a typical Chinese wall‐painting. Raman bands at 1537, 1209 and 1165 cm⁻¹ are identified as discriminating markers for the carotenoid colorant components crocetin and crocin. Copyright © 2009 John Wiley & Sons, Ltd.     

Online coupling of high‐performance liquid chromatography with surface‐enhanced Raman spectroscopy for the identification of historical dyes

High‐performance liquid chromatography (HPLC) is still, today, the technique of choice for the analysis of natural dyes in artistic objects and historical textiles, particularly in association with photodiode array (PDA) detection. In the last two decades, surface‐enhanced Raman spectroscopy (SERS) gained also increasing importance for these investigations thanks to its sensitivity and limited requirements in terms of sample quantity. In favor of SERS, its high specificity in molecular recognition typical of vibrational spectroscopy should be mentioned, whereas this non‐separative technique is obviously disadvantaged in the analyses of mixed chromophores, as is often the case of many natural dyes and also of tints obtained by the combined use of different colorants. An optimized experimental setup combining the two techniques, HPLC‐PDA and SERS, is proposed in the present work, allowing online SERS detection of different dyeing compounds eluted from the HPLC column. Examples are presented concerning some of the colorants most widely used in history, such as morin and luteolin for yellow dyes, alizarin, purpurin, laccaic, kermesic, and carminic acids for red ones, and indigotin for blue tints. Copyright © 2016 John Wiley & Sons, Ltd.     

The use of Raman microscopy and laser desorption ionization mass spectrometry in the examination of synthetic organic pigments in modern works of art

Synthetic organic pigments are widely used in modern and contemporary works of art. They have been examined by a variety of techniques including spectroscopic methods such as Fourier transform infrared spectroscopy, Raman, and X‐ray powder diffraction as well as chromatographic or mass spectrometric techniques such as pyrolysis‐gas chromatography/mass spectrometry and laser desorption ionization mass spectrometry (LDI–MS). Often, a combination of techniques has been used to examine these pigments. This paper describes use of Raman spectroscopy to create a database of colorants including two pigments not previously reported, PO1 and PO2. Then, using Raman spectroscopy in combination with LDI–MS, samples from modern works of art by artists including Mark Rothko, Barnett Newman, and José de Rivera were examined in order to identify the pigments present. One finding was that Rothko used a variety of red pigments over the course of his career including PR11 which has not been previously reported in artwork, and PO2 found with its positional isomer PR1. Knowledge of the colorants serves to inform conservators about display and treatment decisions. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Raman spectroscopy of synthetic organic pigments used in 20th century works of art

Raman microscopy allows a non‐destructive characterisation of inorganic and organic painting materials such as pigments and organic dyestuffs. The objectives of this study are the more recent organic pigments typically present in paintings and other art works from the 20th century. More than 20 organic synthetic pigments from different chemical classes could be identified by Raman spectroscopy using different excitation wavelengths (457.9, 476.5, 487.9, 514.5, 632.8, and 1064 nm). To evaluate the performance for real paint samples, varying paint mixtures of the Hansa Yellow pigment PY 3 and the binding medium Mowilith, a polyvinyl acetate (PVAC) compound, were characterised; PY 3 was determined at a 1 wt% level in the binder. In addition, commercial tube paints containing the quinacridone violet PV 19 were studied. The pigment was clearly identified in all of these more complex oil and acrylic paints. Finally, alizarin (PR 83) and a green copper phthalocyanine pigment (PG 7) could unambiguously be identified by Raman microscopy in the painting ‘Woman with mandolin in yellow and red’ of Max Beckmann dating 1950. The discovery of a red naphthol AS pigment by Raman spectroscopy in a sample from the ‘Three field workers’ by Georg Baselitz (1964/1965) demonstrated that in some cases complementary chromatographic methods are needed for a comprehensive identification of the organic pigments. Copyright © 2008 John Wiley & Sons, Ltd.     

Identification of anthocyanins in plant sources and textiles by surface‐enhanced Raman spectroscopy (SERS)

The aim of the present study was to provide experimental procedures for the identification of anthocyanin‐based dyes used in antiquity. In particular, we assessed the possibility to identify anthocyanins, both in plant extracts and in dyed textiles, by means of surface‐enhanced Raman spectroscopy (SERS), a very chemically specific technique that is moreover sensitive to the changes in structures of molecules, phenomena that occur extensively in the chemistry of anthocyanins. The choice of the plant sources (bilberry, elderberry, sumac, purple corn and hollyhock) was based on their attested use in history as dyeing matters. Suitable extraction and pre‐treatment procedures were optimized both for plant sources (berries, cob glumes and flowers) and textiles dyed with such sources in the laboratory, followed by SERS analyses at different pH values. Finally, special attention was paid to the well‐known instability of anthocyanins: dyed wool samples were exposed to artificial aging in order to verify the possibility to identify such molecules also in faded textiles. The achievement of reliable surface‐enhanced Raman spectra from these samples encourages us to suggest the protocol for the analysis of historical objects. Copyright © 2015 John Wiley & Sons, Ltd.     

New advancements in SERS dye detection using interfaced SEM and Raman spectromicroscopy (μRS)

In the past decade Surface Enhanced Raman Scattering (SERS) has emerged as a powerful technique for the analysis of artistic, historical and archaeological material culture. However, the identification of organic compounds in complex samples using SERS can be challenging owing to the complexity in optimizing the adsorption of target analytes onto the plasmonic substrate and the difficulty to identify proper areas on the sample for robust SERS analysis using optical systems. Scanning electron microscopy (SEM) interfaced with Raman spectromicroscopy (μRS) provides an ideal hyphenated system to overcome the last challenge by: (1) evaluating the nanoparticles coverage/distribution on the sample and (2) locating suitable areas for successful and reproducible SERS analysis. In this paper we demonstrate the potential of a system interfacing SEM and μRS for single fiber, extractionless analysis in the characterization of dyes from reference collections and archaeological textiles. Copyright © 2015 John Wiley & Sons, Ltd.     

Crocoite PbCrO4 and mimetite Pb5(AsO4)3Cl: rare minerals in highly degraded mediaeval murals in Northern Bohemia

Mural paintings of exceptional quality, which can be discerned in spite of their extensive mechanical damage and colour fading, have been uncovered in the church of St. Gallus in Kuřívody, Northern Bohemia, dated to the second half of the 13th century. Materials research with particular use of portable X‐ray fluorescence, Raman micro‐spectroscopy and powder X‐ray micro‐diffraction revealed the presence of rare pigments. In Kuřívody, it is only a second identification of intentionally used yellow mineral crocoite (PbCrO₄) in European art. Its identification is facilitated by providing a very good Raman scattering, even when present in small amounts in fragmentarily preserved colour layers. Light yellow mimetite (Pb₅(AsO₄)₃Cl) was never before mentioned as intentionally used pigment in Europe. Its finding in Kuřívody, however, corresponds more likely with undesirable physical–chemical conditions causing its formation by alteration of orpiment (As₂S₃) and minium (Pb₃O₄). Obtained results highlight the importance of Raman spectroscopy for direct identification of mineral pigments in low concentrations, which may be crucial for interpreting cultural heritage objects in historical context. By materials, the almost forgotten paintings in Kuřívody can be seen as outstanding and rare example of ancient artistic tradition that has spread to Europe from Mediterranean in early Middle Ages. After all, mineral crocoite was already used by ancient Egyptians to paint sarcophagi and degraded orpiment decorates the walls of the Nefertari's tomb in Thebes. Copyright © 2014 John Wiley & Sons, Ltd.     

The study of the mural painting in the 12th century monastery of Santa Maria delle Cerrate (Puglia‐Italy): characterization of materials and techniques used

A multidisciplinary research was conducted by the University of Salento in collaboration with the Lecce Provincial Museum, in order to study different forms of art widespread in the Salento peninsula (Southern Italy) very valuable from an artistic point of view and important as driving force for the tourism of the area. In this research, the archaeometrical analysis was used to study the first cycle of paintings of the church of Santa Maria delle Cerrate, an italo‐greek monastery located in the country about 15 km north‐east of Lecce, probably built in the 12th century. Microscopic, chromatographic and spectrometric techniques were used: optical microscopy was used to study samples and the relevant stratigraphy, micro‐Raman Spectroscopy to identify pigments and Gas Chromatography with Mass Spectrometric Detection to investigate the techniques masters used to decorate the monastery church. Further information on organic and inorganic materials present in the samples were obtained from Fourier transform infrared analysis in attenuated total reflectance. Materials and techniques were clearly ascertained, and, interestingly, pigments were applied both by fresco and egg‐based tempera. Among the various pigments detected, the identification of both lapis lazuli and lead white opened new perspectives both from the historical and conservative points of view. Copyright © 2013 John Wiley & Sons, Ltd.     

1945年银行票据样品印刷颜料无损鉴定

利用超景深三维视频显微镜、激光显微共聚焦拉曼光谱仪、扫描电镜-能谱仪等,对一张1945年银行票据样品的印刷颜料进行测试分析,结果显示该票据印刷使用了颜料红146和颜料红53∶1等有机颜料,以及朱砂、碳黑、普鲁士蓝、副雄黄和χ构型雄黄等无机颜料,并推测棕黑色手写字迹由蓝黑墨水老化褪色形成。票据中各处色块多为单一呈色,有两处印章由朱砂与不同晶型的雄黄共同呈色,并且首次发现χ构型雄黄和副雄黄作为印刷颜料使用。研究表明,上述三项技术的联用可以成功地对纸质品上的有机及无机颜料进行无损鉴定,在纸质文物研究中具有广阔的应用前景。     

Investigation of natural dyes and ancient textiles from korea using TOF-SIMS

The identification of the colorants used on ancient textiles provides a historical pathway to the understanding of the processes associated with one of the oldest of chemical technologies, namely textile dyeing. In this paper, time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to detect dyes on textiles avoiding the time-consuming and destructive extraction procedures necessary for the spectrophotometric and chromatographic methods previously used. The plant dyes investigated belong to a variety of chemical groups, which include curcumin, crocin, carthamin, purpurin, alizarin, brazilin, shikonin, and indigo. Reference textile samples were prepared with dye extracts of plants and were characterized by TOF-SIMS. TOF-SIMS spectra for the dyed textiles showed element ions from metallic mordants, specific fragment ions, and molecular ions from organic dyes. Remnant dyes on excavated textiles have also been identified using TOF-SIMS. The ancient textile sample showed the presence of indigo clearly, although the fiber itself had degraded badly. From the results, it was concluded that most of plant dyes can be identified with TOF-SIMS and it is a very promising technique for the archaeology field.     

Fourier‐transform surface‐enhanced Raman spectroscopy (FT‐SERS) applied to the identification of natural dyes in textile fibers: an extractionless approach to the analysis

In the present study, an application of a silver colloid substrate in order to obtain Fourier‐transform surface‐enhanced Raman (FT‐SER) spectra of natural historical dyes is presented. In detail, we collected a spectral database from solutions of pure dyes and then we carried out extractionless both hydrolysis and non‐hydrolysis FT‐SERS analyses on wool fibers previously dyed in our laboratory and on ancient textiles. The term ‘extractionless’ refers to a method of SERS analysis applied directly on the fiber, thus avoiding the extraction of dyes from textile samples. The combination of a low‐energy source of radiation, as in the FT‐Raman technique, with SER spectroscopy can bring the important advantage of reducing the fluorescence typical of ancient samples and organic dyes. In some historical textile samples, for which SER spectra by use of visible excitation could not be obtained, the FT‐SER spectrum of an iron‐gall dye was recorded without hydrolysis, while, with an HF hydrolysis pre‐treatment on ancient fibers, madder, lac dye and brazilwood were clearly recognized. Copyright © 2014 John Wiley & Sons, Ltd.     

The use of combined synchrotron radiation micro FT-IR and XRD for the characterization of Romanesque wall paintings

The high analytical sensitivity and high spatial resolution of synchrotron radiation-based techniques, in particular SR-XRD and SR-FT-IR, allows the identification of complex micrometric mixtures of compounds that constitute the different layers of ancient paintings. The reliability of the measurements even with an extremely small amount of sampled material is very high, and this is particularly important when analyzing art works. Furthermore, the micro size (10×10μm for FT-IR and 30 to 50 μm squared spot size for XRD) of the beam enables one to obtain detailed compositional profiles from the different chromatic and preparation layers. The sensitivity of the techniques is high enough for the determination of minor and trace compounds, such as reaction and weathering compounds. We report here the identification of pigments in the Romanesque wall paintings found in situ in the church of Saint Eulàlia of Unha place in the Aran valley (central Pyrenees). During the first centuries of the second millennium numerous religious buildings were built in Western Europe in the Romanesque style. In particular, a great number of churches were built in the Pyrenees, most of which were decorated with wall paintings. Although only a few of these paintings have survived, they represent one of the most important collections of Romanesque art, both for their quantity and quality. A full identification of the pigments, binder, supports, and reaction and weathering compounds has been obtained. The results obtained, in particular aerinite as a pigment, indicate a clear connection between the paintings found in this Occitanian church and the Catalan Romanesque paintings from the south bound of the Pyrenees. PACS 61.10.Nz; 07.85.Qe; 82.80.Gk     

Surface‐enhanced Raman scattering (SERS) and complementary techniques applied for the investigation of an Italian cultural heritage canvas

A cultural heritage canvas from the early 19^th century, painted by the Vaccaro brothers for the church of Niscemi, province of Caltanissetta, Sicily, was analyzed using Fourier transform (FT)‐Raman, attenuated total reflectance‐FT‐infrared and surface enhanced Raman scattering (SERS) spectroscopy. The painting, still used in religious rites related to the Easter mass (‘la calata da tila’), depicts the scene of the Crucifixion and is executed in a scarce palette, with white, green and blue colors. Analysing vibrational data in conjunction with scanning electron microscopy and solid ‐state ¹³C‐NMR signals of the linen threads, we were able to offer valuable insight into the painting technique, unknown prior to this study. SERS is usually employed in artwork diagnosis for the identification of organic lakes and dyes. Due to its sensitivity, SERS has been successfully applied for the detection of either organic painting materials (indigo) that are usually not resolved by conventional Raman spectroscopy or of inorganic pigments difficult to observe in the presence of highly fluorescent aged organic supports or binders. To the best of our knowledge, this is also the first report on the SERS investigation of flax used in linen from cultural heritage objects using Ag colloidal nanoparticles. Copyright © 2012 John Wiley & Sons, Ltd.     

SERS detection of red organic dyes in Ag‐agar gel

Micro‐Raman spectroscopy has been widely employed in the last few years for the study of artworks, allowing for the characterization of a high class of pictorial materials. However, the detection of organic dyes by conventional Raman spectroscopy is quite difficult, due to the high fluorescence provided by these compounds. Recently, remarkable improvements have been achieved by the introduction of the surface enhanced Raman spectroscopy (SERS) technique for the analysis of organic dyes. In the present work, a new method is presented, based on the use of a SERS probe made of agar‐agar coupled with silver nanoparticles, for a non‐destructive and minimally invasive micro‐extraction of dyes from textiles. Ag‐agar gel has been tested first on textile mock‐ups dyed with alizarin, purpurin and carminic acid. SERS measurements have been performed adopting laser light excitations at 514.5 and 785 nm of a micro‐Raman setup. Highly structured SERS band intensities have been obtained. After having verified the safety of the method by colorimetric, X‐ray fluorescence and attenuated total reflectance Fourier transform infrared techniques, a real case, a pre‐Columbian piece of textile, have been investigated by Ag‐agar gel. This cutting‐edge method offers new possibilities for a sensitive and non‐destructive analysis of fluorescent materials. Copyright © 2012 John Wiley & Sons, Ltd.     

拉曼光谱在考古中的应用

拉曼光谱分析是一种无损快速分析技术,随着显微拉曼光谱仪的不断改进和FT—显微拉曼光谱仪的使用,它已经用于珍贵艺术品、手稿、颜料、古陶瓷和壁画等领域的考古和鉴定研究。本文对这些应用进行了简单概述。     

Pigment analysis of Portuguese portrait miniatures of 17th and 18th centuries by Raman Microscopy and SEM‐EDS

Seventeen Portuguese miniature portraits on copper support from the Évora Museum collection (Portugal) were analyzed in situ and nondestructively by Raman microscopy (RM), SEM‐EDS, and stereomicroscopy. This work constitutes a great breakthrough in the study of miniature paintings from the 17^th and 18^th centuries, since the chemical information known about this unique kind of paintings are still scarce, and in particular, this exclusive collection was never been subjected to any physicochemical study. In this work, each portrait was examined in detail in order to characterize the pigments palette used by the miniaturists. The μ‐Raman analysis, in particular, guaranteed an exceptional visualization and good individual identification of small grains of pigments and other constituents of the pictorial layer. Using this technique, 19 compounds were identified, including bluish black covellite, a pigment rarely found in oil paintings. SEM‐EDS was used as an important complementary technique to confirm the chemical nature of some pigments and to identify shell gold (gold dust) in some portraits. Overall, the pigments identified in this large set of old paintings are broadly consistent with those mentioned in the painting treatises of that time or reported in other more modern bibliographic sources. Copyright © 2014 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman spectroscopy of various madder species on wool fibers: the role of pseudopurpurin in the interpretation of the spectra

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.     

Multivariate analysis of combined Raman and fibre‐optic reflectance spectra for the identification of binder materials in simulated medieval paints

The non‐invasive identification of paint materials used in works of art is essential, both for preserving and restoring them, and also for understanding and verifying the history surrounding their creation. As such, the development of suitable non‐invasive techniques has received much interest in recent years. We have investigated the use of Fourier transform (FT)‐Raman spectroscopy and fibre‐optic reflectance spectroscopy (FORS), together with multivariate principal‐component analysis (PCA) techniques, in order to identify the pigment and binding materials used in made‐up samples representative of real artwork. We demonstrate that both types of spectroscopy provide complementary information which can be used to identify the pigments and binders in paint samples. We show that PCA with FT‐Raman spectra can be used to assist in the identification of oil‐based binders, and that the additional data provided by FORS spectra enables PCA on combined spectra to identify more complex proteinaceious and polysaccharide‐based binding media. The results presented here demonstrate that multivariate analyses of lead‐based paints, using data measured by FT‐Raman and FORS in conjunction, have much potential for identifying individual pigments and binders in paint samples. This provides a path towards computer‐assisted characterisation of paint materials on artwork. Copyright © 2013 John Wiley & Sons, Ltd.