A Raman spectroscopic study of the Mapungubwe oblates: glass trade beads excavated at an Iron Age archaeological site in South Africa

Oblate seed beads (2–4 mm) excavated on Mapungubwe hill, an Iron Age site in South Africa, were analysed with Raman microscopy and supportive techniques to determine the glass technology and pigments used to produce the beads. The Raman spectra and XRF analysis of the beads classify the glass as a typical soda/lime/potash glass similar to Islamic glass from the 8th century (Ommayad), but with higher levels of aluminium, iron and magnesium. The turquoise, bright green, bright yellow and orange colours were obtained by utilizing a combination of cassiterite (SnO₂) and lead tin yellow type II (PbSn_1−xSi_xO₃). Doping with cobalt and manganese produced dark blue and plum‐coloured beads. The Fe‐S chromophore was detected through its resonance‐enhanced spectrum in the black beads. Corrosion of the black beads was investigated and an organic phase detected on the beads, which might have influenced the corrosion process. This detailed profile of the glass technology used to produce the Mapungubwe oblates might eventually help to determine their provenance. Copyright © 2007 John Wiley & Sons, Ltd.     

Testing of Raman spectroscopy as a non‐invasive tool for the investigation of glass‐protected pastels

Five French pastels and a sanguine drawing dating from the 17th to the 20th century were studied by Raman spectroscopy. Different operative conditions were used: the pastels were investigated through their protective glass, and the results obtained were compared with those obtained after removing the glass and after sampling a micrometric particle of pigment. Different parameters (wavelengths, powers of excitation and objectives) were tested in order to assess the optimal procedure of analysis for this fragile work of art. The results obtained for black (carbons), yellow (chrome/cobalt yellow), red (lead oxide, vermillion, orpiment), brown (red lead and chrome yellow), blue (Prussian blue, lapis lazuli/ultramarine), green (mixture of above blue and yellow pigments) and white (calcite, lead white, anatase) pigments are presented and the consistency of the pigments' period of use with the dating proposed for each pastel is evaluated. In one of the pastels, the blackening of the carnation colour made of an unstable mixture of lead white, red lead and vermilion was studied. Copyright © 2010 John Wiley & Sons, Ltd.     

Inside the glassmaker technology: search of Raman criteria to discriminate between Emile Gallé and Philippe‐Joseph Brocard enamels and pigment signatures

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 Gallé have been analysed using a mobile Raman instrument at the Musée des arts décoratifs (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 Gallé (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.     

Evolution of past enamel technology and metal conservation issues: the case of two Byzantine style bindings

The results of a Raman spectroscopic study of the cloisonne’ and basse‐taille enamels, which beautify two Byzantine style bindings from the Marciana Library (Venice), namely the Lat. III,111 and the MsGR.I.53 codexes, are presented in this work. The first binding dates back to the 13th century and was subject to an early restoration work in the 14th century, when new enamels substituted four originals. The second binding, from the 15th century, shows a lower number of enamels, all originals, and with a larger color palette. The white and yellow enamels of both codexes were successfully characterized and the red ones, where hematite was not used. Interestingly the white and yellow color of the 13th century enamels of the Lat. III,111 codex has been obtained by an ancient technique of the glass technology, which was already obsolete in the 13th century, and is based on the use of calcium antimonate and Naples yellow. The white color in the other binding's enamels have been instead obtained by using cassiterite, according to the tradition of the time. Cassiterite was also mixed to Naples yellow in the enamels of the MsGR.I.53 codex, to change the yellow hue. The identification of agents determining some colors is instead uncertain or not feasible by Raman spectroscopy. The transparency of the 14th century enamels of the Lat. III,111 codex has allowed the comparison of metal degradation below the enamels and in regions exposed to the atmosphere. Copyright © 2012 John Wiley & Sons, Ltd.     

Identification of Pigments in Colored Layers of a Painting by Raman Spectroscopy

Using the method of Raman spectroscopy the pigment composition is investigated of, and the brushwork technique used in, the original layer of a 19th century painting is established. It is an overdoor worked, presumably, by Antoine Jean-Etienne Faivre. It is established that the artist used the following pigments: cinnabar and dyes on the basis of goethite and hematite (for red, yellow–orange, and brown shades), ultramarine and Prussian blue (for blue shades), and Emerald green and a mixture of blue and yellow shades (to obtain a green color). It is determined that white lead was used a primer.     

Testing of Raman spectroscopy as a non‐invasive tool for the investigation of glass‐protected miniature portraits

Six French miniature portraits on ivory and paper dating back to the 18th to 19th centuries have been studied by Raman spectroscopy. The miniatures have been investigated through their protective glass cover using different operating conditions: various laser wavelengths (1064, 785 and 532 nm), spectrometers (fixed and mobile) and objectives (10× to 200×). The results obtained for black (carbon), grey (carbon + chalk), red (lead oxide, vermillion), blue (Prussian or phthalocyanine blue), green (emerald or Paris green) and white (lead white) pigments are presented. The consistency of the period of use of the pigments with the proposed dating for each artwork is evaluated. Attention is paid to the analysis of the ivory substrates (assigned to Asian elephant ivory) and to the protective glass. Copyright © 2011 John Wiley & Sons, Ltd.     

Pigment study by Raman microscopy of 23 paintings by the Portuguese artist Henrique Pousão (1859–1884)

Twenty‐three paintings by Henrique Pousão—a 19th century Portuguese painter—belonging to the collection of Museu Nacional Soares dos Reis, Porto, Portugal, were analysed by Raman microscopy. The fine focus of a 100× objective allowed the visualisation and individual identification of small grains. As a result, thirty‐seven compounds, namely, anatase, barium white, basic lead sulfate, brochantite, cadmium red, cadmium yellow, calcium carbonate, carbon‐based black, celadonite, chrome green, chrome orange, chrome yellow, cobalt blue, cochineal lake, copper sulfide, emerald green, iron(III) oxyhydroxide, iron(III) oxide, kaolinite, lead antimonate yellow, lead carbonate, lead white, lead sulfate, madder lake, malachite, Prussian blue, quartz, realgar/pararealgar, red lead, rutile, Scheele's green, strontium yellow, ultramarine blue, vermilion, viridian, zinc white and zinc yellow, were identified. Not all these compounds are pigments; some are extenders, others trace components and others probably products of reactions between pigments. Special attention was given to the Raman characterisation of celadonite, chrome orange, basic lead sulfate and lead antimonate yellow. Complementary techniques were used to confirm the identities of certain pigments and to characterise reference samples. Pousão, whose work has not previously been studied spectroscopically, was found to have used a remarkably wide range of pigments over his painting periods, without showing significant preference for any particular set of pigments. Copyright © 2007 John Wiley & Sons, Ltd.     

Raman classification of glass beads excavated on Mapungubwe hill and K2, two archaeological sites in South Africa

About 200 coloured glass beads (red, yellow, green, blue, white, black, pink, plum) excavated on Mapungubwe hill and at K2, archaeological sites in the Limpopo valley South Africa, were studied with Raman scattering. This is also the most southern site in Africa where evidence for glass reworking has been found. The glass matrix of the beads was classified according to its Raman signature into three main subgroups and corroded glass could also be identified. At least seven different chromophores or pigments (lazurite, lead tin yellow type II, Ca/Pb arsenate, chromate, calcium antimonate, Fe–S ‘amber’ and a spinel) were identified. Many of the pigments were manufactured after the 13th century, confirming the presence of modern beads in the archaeological record. This calls for further research to find a way to reconcile the carbon dating of the hill, which currently gives the last occupation date on the hill as 1290 AD with the physical evidence of the modern beads excavated on the hill. The results are discussed in terms of the glass production origin of the beads (Europe, Mediterranean area, India, China). Copyright © 2011 John Wiley & Sons, Ltd.     

On‐and off‐site Raman study of rock‐shelter paintings at world‐heritage site of Bhimbetka

Rock‐shelter paintings of Bhimbetka world‐heritage site near Bhopal, India have been investigated using a portable Raman spectrometer. These paintings in the rock shelters belong to periods starting from pre‐historic to the 19th century AD (Gond period). In addition, tiny fragments of pigments (100–200 µm in size) extracted from some of the artworks were also studied in laboratory using a micro‐Raman spectrometer and analyzed using energy‐dispersive X‐ray analysis for elemental composition. Based on the Raman spectra and the elemental analysis mineral‐based pigments such as calcite, gypsum, hematite, whewellite, and goethite could be identified. A comparison of the spectra recorded on‐site using a light‐weight portable spectrometer with those using laboratory equipment is also made and discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterisation of inorganic pigments in ancient glass beads by means of Raman microspectroscopy,microprobe analysis and X‐ray diffractometry

Ancient coloured glass beads from Sri Lanka and Oman were analysed by Raman microspectroscopy for non‐destructive identification of inorganic pigments in the glass. Calcium phosphate (Ca₃(PO₄)₂), cassiterite (SnO₂), cuprite (Cu₂O) and a Pb(Sn,Si)O₃‐type lead tin oxide were found to be used as colouring agents. Moreover, a distinction between lead‐based and alkali‐based glass matrices could be made. Electron microprobe analysis and X‐ray diffractometry were performed to show the capability of Raman microspectroscopy in comparison to these methods for answering archaeometric questions. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman scattering features of lead pyroantimonate compounds: implication for the non‐invasive identification of yellow pigments on ancient ceramics. Part II. In situ characterisation of Renaissance plates by portable micro‐Raman and XRF studies

The effectiveness of Raman spectroscopy (using a bench‐top system on standard pigments) for the characterisation of modified lead antimonate yellows was demonstrated in the already published Part I. The knowledge gained is employed here for the study of yellow glazes on genuine Renaissance plates with the aim of identifying non‐invasively lead pyroantimonate compounds by portable micro‐Raman equipment. The investigation was carried out directly on site, at the Victoria and Albert Museum (London, UK) and at the Museo Statale d'Arte Medievale di Arezzo (Arezzo, Italy), combining Raman and X‐ray fluorescence analyses. In addition to the spectral features of both unmodified Naples yellow and Sn‐ and Zn‐modified lead antimonate compounds, the Raman patterns related to partially modified pyrochlore structures were observed. For this reason, the possible Sn‐induced modification of Naples yellow by cassiterite (SnO₂), present within the glaze as opacifier was explored on lead antimonate yellow glaze mock‐ups fired at different temperatures. Copyright © 2010 John Wiley & Sons, Ltd.     

The use of micro-XRD for the study of glaze color decorations

The compounds responsible for the colors and decorations in glass and glazed ceramics include: coloring agents (transition-metal ions), pigments (micro- and nanoprecipitates of compounds that either do not dissolve or recrystallize in the glassy matrix) and opacifiers (microcrystalline compounds with high light scattering capability). Their composition, structure and range of stability are highly dependent not only on the composition but also on the procedures followed to obtain them. Chemical composition of the colorants and crystallites may be obtained by means of SEM-EDX and WDX. Synchrotron radiation micro-X-ray diffraction (SR-micro-XRD) has a small beam size adequate (10 to 50 microns footprint size) to obtain the structural information of crystalline compounds and high brilliance, optimal for determining the crystallites even when present in low amounts. In addition, in glass decorations the crystallites often appear forming thin layers (from 10 to 100 micrometers thick) and they show a depth-dependent composition and crystal structure. Their nature and distribution across the glass/glaze decorations gives direct information on the technology of production and stability and may be related to the color and appearance. A selection of glass and glaze coloring agents and decorations are studied by means of SR-micro-XRD and SEM-EDX including: manganese brown, antimony yellow, red copper lusters and cobalt blue. The selection includes Medieval (Islamic, and Hispano Moresque) and Renaissance tin-glazed ceramics from the 10th to the 17th century AD.     

Micro‐Raman and stratigraphic studies of the paintings on the ‘Cembalo’ model musical instrument (A.D. 1650) and laser‐induced degradation of the detected pigments

Micro‐fragments of the painted part of the ‘Cembalo’ model by Michele Todini (1625–1689) are investigated. The technique used for painting the terracotta base was studied via the stratigraphic analyses. No background layer of inorganic materials, e.g. gypsum, was found. To prevent absorption effects due to the terracotta porosity, a very thin layer of proteinaceous material was probably used. The micro‐Raman analyses have revealed the use of pigments currently used in the post‐Renaissance period (lead white, indigo, yellow of iron hydroxide, gypsum, hematite and carbon black) mixed with a pigment, the Prussian blue, discovered in A.D . 1704. This raises the authenticity problem of the work of art, a problem analysed and discussed in presenting the history of the work of art, and after the pigment study. The presence of degraded lead white is recognized via the laser‐induced degradation of the irradiated material. The possibility of a restoring action of the painted parts, as opposite to the non‐originality of the work, is considered and discussed. Since most part of the investigated pigments shows laser‐induced effects, a careful study of this phenomenon is performed by using the modern counterparts of the ancient pigments. For different laser powers, the temperatures of the investigated zones have been obtained via the detailed balance principle and connected to the laser‐induced degradation effects. Copyright © 2007 John Wiley & Sons, Ltd.     

On‐site analysis of Limoges enamels from sixteenth to nineteenth centuries: an attempt to differentiate between genuine artefacts and copies

A selection of 15 painted enamels, most of which belong to Limoges productions, from 1500 to 1900 A.D. , has been studied on‐site in the storage rooms of musée des Arts décoratifs in Paris. The Raman signatures of the transparent and/or opacified glass matrix are discussed and compared with those which were previously recorded on glazed pottery, enamelled and stained glasses as well as Chinese cloisonné enamels. Analysed enamels mostly belong to soda‐lime‐based glass. Three types of compositions such as soda‐lime (fifteenth to sixteenth century), soda‐rich (fifteenth, sixteenth/nineteenth centuries) and lead‐potash‐lime (sixteenth and nineteenth centuries) are identified on the basis of the Raman signature of the glaze according to the wavenumber maxima of the Si O stretching and bending multiplets. The pigment signatures are similar to those recorded on ceramic glazes and glass enamels, which proves the similarity of the technologies. Cassiterite as an opacifier and hematite red and Naples yellow pigment variations give characteristic Raman signatures. The presence of lead arsenate as a pigment opacifier in nineteenth‐century samples is confirmed. Attempts are made to establish tools for the differentiation between genuine artefacts and nineteenth‐century restoration or fakes. Copyright © 2010 John Wiley & Sons, Ltd.     

A combined analytical approach applied to Medieval wall paintings from Puglia (Italy): The study of painting techniques and its conservation state

A combined analytical approach has been applied to the wall paintings, dated from 10th to 14th centuries, of the Santi Stefani crypt at Vaste (Lecce, Southern Italy). These paintings are a precious testimony of Medieval art in Southern Italy. However, the church shows problems of damp as well as clear evidences of flora, fungi and mold presence, and there is little knowledge of the pictorial methodologies used. Raman spectroscopy allowed to determine the palette and to reconstruct the worksite and the chronological sequence of the various paint layers. Kaolinite, calcite, carbon black, hematite, massicot, goethite, indigo and azurite were identified as pigments along with synthetic pigments, like phthalocyanine blue and chrome yellow. Attenuated total reflectance‐Fourier transform infrared spectroscopy suggested the presence of egg as a binder in some pictorial layers. The conservation state of the crypt is poor, and detachments of pigmented layers are frequent because of the presence of subflorescence and efflorescence: nitrate, sulfate and chloride salts have been identified spectroscopically and quantified by ion chromatography. The extensive use of kaolinite in Santi Stefani, actually not uncommon in Medieval art, is observed for the first time in a crypt of Puglia: its use to stabilize some pigments and to improve their adhesion on substrate is proposed. Copyright © 2015 John Wiley & Sons, Ltd.     

Raman analysis assessed by Fourier‐Transformed infrared and X‐ray fluorescence spectroscopies: a multi‐analytical approach of ancient chromolithographs from the 19th century

A set of chromolithographs from the 19th century were analysed to identify the fillers and pigments used for their elaboration. Because of the delicacy of the chromolithographs, the research involved the use of Raman, Fourier‐transform infrared and energy dispersive X‐ray fluorescence spectroscopies for a complete characterization of the works on paper without removing any microsamples. Despite the high fluorescence of the samples when analyzed by Raman spectroscopy, in this paper, we demonstrated that ink spectra can be successfully enhanced by subtracting the spectra of the supporting background paper. The results of the study showed that, apparently, the lithographer used a limited range of common inorganic pigments from the 19th century (carbon black, chrome yellow, Prussian blue, red ochre, red lead and vermilion) together with organic pigments (indigo blue, gamboge and a red organic pigment). The study also found that despite the fact that during the 19th and early 20th century the use of mixtures of several pigments was a common practice, unusual admixtures were used for the preparation of some colours of the studied chromolithographs. Copyright © 2011 John Wiley & Sons, Ltd.     

The first spectroscopic analysis of Ethiopian prehistoric rock painting

An extensive micro‐Raman spectroscopic study of prehistoric rock paintings found in Hararghe region, Ethiopia, was carried out, with the aim to evaluate the production skill of the local artist and the period of production of the discovered paintings. Attenuated Total Reflection Fourier Transform Infrared (ATR‐FTIR) Spectroscopy and Laser Induced Breakdown Spectroscopy (LIBS) were used as auxiliary techniques. Micro sampling were carried out on parts of red, white, black painting figures representing domestic and wild animals. The pigments used by artists were hematite for red color, calcite or gypsum for white color, and carbonaceous material for black coloration. A green pigment was also investigated; it resulted made of green earth. A consistent amount of Ca‐oxalate was found particularly on red samples as well as on the white ones. Former studies attributed oxalates origin to a biological substrate attack, whereas in the present case Ca‐oxalate is ascribed to the use of an organic stuff to spread properly the pigments on the substrate.Principal Component Analysis was performed on the hematite spectra; it evinced that the spectral features could be indicative of different sites and of the relative age.1These novel evaluations put into new perspective the knowledge about rock art pictorial technology of the Horn of Africa. Copyright © 2011 John Wiley & Sons, Ltd.     

Portable XRF study of pigments applied in Juan Hispalense’s 15th century panel painting

Several medieval paintings and polychrome sculptures have been analysed in the frame of a collaboration between the Fine Arts Museum of Seville and the National Centre of Accelerators, dedicated to a non‐destructive study of artworks that belong to the wide museum’s collection. Among the oldest artworks in the collection is the panel painting Archangel St. Michael attributed to Juan Hispalense, one of the first painters in the 15th‐century Seville known by name. The panel was analysed by a portable X‐ray fluorescence (XRF) to get more information about the pigments applied and to identify possible later interventions. The results showed that the pigments were those commonly used in that period. Lead white was found in the preparation of the painting and in colour layers. For yellow colour, yellow ochre was used, while for the red one, the painter usually mixed red earth and vermillion. Blue pigment is azurite, while the copper‐based green one could not be determined more specifically by XRF. Brown colour is made with yellow ochre and organic black or, in some cases, umbra. Black pigment is probably bone or ivory black. Many decorative parts of the panel are gilded, which were confirmed by Au peaks. Later interventions were carried out on the base of Ti–Zn white mixed with earth pigments, while for green areas such as Archangel's wings also chrome green was applied. The research is part of a larger study which is still going on, whose aim is to gain more knowledge about the 15th‐ and 16th‐century Spanish painting and polychromy. Copyright © 2011 John Wiley & Sons, Ltd.     

Non‐destructive identification of pigments printed on six Imperial China Engraved Coiling Dragon stamps

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.     

Raman Characterization of Pigments in Painted Beams and a Wall Painting Discovered in the San Francisco Church in Santiago,Chile

A material characterization of two artworks discovered in the San Francisco Church, Santiago, Chile, was performed using micro-Raman spectroscopy. Structural painted beams and a wall painting that belong to the same time period, between the end of the 17th and 19th centuries, were analyzed. The cross-section samples of both artworks were characterized and animal protein was identified in the ground layer in both cases. The supporting material of the beams was identified as cypress wood, and a rag paper layer was used as a base for the paint layer, which is composed mainly of a white ground layer on which the color was subsequently added; the yellow pigments are orpiment and chrome yellow; the green color probably arises from a mixture of orpiment, red lead, ultramarine blue, and calcite. A complete analysis of the materials using complementary techniques such as microchemistry and optical microscopy indicates that the mural was painted using a mixed technique and that organic and inorganic pigments were used. The identification of the synthetic pigment ultramarine blue in some blue areas of the wall revealed a modification of the wall painting in the 19th century; dark blue areas resulted from a mixture of indigo, palygorskite, and lazurite.