Ultrasensitive chemiluminescent immunochemical identification and localization of protein components in painting cross-sections by microscope low-light imaging

The characterization and localization of proteins and other organic components in the complex stratigraphy of paintings is crucial for authentication and studies of painting techniques. With this aim we have developed a new ultrasensitive immunochemical procedure for the detection of the protein ovalbumin (chicken egg white albumin), present in binding media or varnishes, in painting cross-sections. The technique is based on chemiluminescence imaging detection combined with optical microscopy, and allowed the sensitive localization of the target protein in cross-sections with high spatial resolution. In order to evaluate its performance, the method was first applied to standard samples (also containing different common pigments), then used for the localization of ovalbumin in samples obtained from a Renaissance wood painting.     

Characterization of Wall Paintings of the Harem Court in the Alhambra Monumental Ensemble: Advantages and Limitations of In Situ Analysis

Non-invasive techniques (X-ray fluorescence, XRF, and Raman spectroscopy) were used for the study of the Hispano Muslim wall paintings. Principal component analysis (PCA) was performed on the semi-quantitative XRF results directly provided by the in-built factory calibrations with minimum user manipulation. The results obtained were satisfactory and highlighted differences and similarities among the measurement points. In this way, it was possible to differentiate the decorations carried out on gypsum plasterwork and the wall paintings over lime plaster. The color palette, revealed by combining the results from XRF and Raman spectroscopies, comprised the pigments hematite, lapis lazuli, cinnabar (in poor conservation state), and possibly, carbon. Evidence of past interventions was also provided by PCA on XRF data, which detected the presence of Pb, Ba, and Zn in some areas. Furthermore, the preparation layers have been studied in detail on cross-sections of two microsamples. Several layers of lime plaster with a compact microstructure have been observed. The characteristic of the pictorial layer and the identification of calcium oxalate point to the use of a secco-technique. The main alteration identified was a gypsum surface layer covering the painting and signs of plaster deterioration due to gypsum migration to more internal areas. Finally, the comparison with the observations made by restorers in previous interventions on these paintings revealed the importance of the representativeness gained with the in situ study, which enabled the analysis of a high number of areas.     

Raman microspectrometric investigation of wall paintings in S. Giovanni Evangelista Abbey in Parma: a comparison between two artists of the 16th century

Micro-Raman spectroscopy, combined with gas chromatography and ultra-violet fluorescence photography, was used to study some wall paintings in the S. Giovanni Evangelista Abbey in Parma, Italy. The restoration of some painted chapels enabled a comparison between two painters of the 16th century: Parmigianino (Girolamo Francesco Maria Mazzola, 1503-1540) and Michelangelo Anselmi (1492?-1556?). Micro-Raman spectroscopy determined the palette used by the artists, leading to the identification of different white, yellow, red, brown, green, blue and black pigments. Some pigments are evidence of later restorations. Gas chromatography combined with mass spectroscopy revealed the presence of organic binding media and enabled to distinguish between fresco and secco paintings.     

Combined use of FORS,XRF and Raman spectroscopy in the study of mural paintings in the Aosta Valley (Italy)

Mural paintings which decorate the external façade and the internal apsidal wall of a chapel dedicated to St. Maxime and located at Challand St. Victor in the Aosta Valley (Italy) have been analysed with a combined approach involving high-resolution fibre-optic reflectance spectroscopy (FORS), X-ray fluorescence (XRF) spectrometry and Raman spectroscopy. The paintings are attributed to Giacomino from Ivrea, a painter active around the mid-fifteenth century. In order to characterise the palette used by the painter and to yield information useful to restorers, the cited techniques were used either in situ with portable instruments and in laboratory, working on micro samples withdrawn from paintings. The global analytical approach, though not entirely non-invasive, can indeed be considered non-destructive as multiple analyses, including SEM-EDX, could be carried out on the micro samples, exploiting the features of each technique. On the basis of the information obtained, the palette was found to be composed of typical fresco pigments such as calcite, azurite, malachite, vermilion, red and yellow ochres. A particular situation was noted for black pigments since the presence of graphite, rather than wood or lamp carbon, was found, possibly related to the presence of graphite deposits in the Aosta Valley. Furthermore, the presence of smalt superimposed to azurite in areas showing evidence of repainting was detected, suggesting that paintings were subjected to retouching at a relatively early stage after the original execution. Finally, the presence of tin foils, used to decorate haloes of Evangelists, was ascertained.     

The Russian avant-garde painting palette--documentary and physicochemical study of inorganic colorants

In the present article an attempt is being made to elucidate the inorganic colorants encountered in the Russian avant-garde painting palette by a combined art historical, documentary and physicochemical investigation; and to examine the influence of environmental factors on the chromatic profile originally sought by the artist. The overall approach based on written sources is confirmed by measurements on representative paintings from the Costakis Collection in the State Museum for Contemporary Art, Thessaloniki. The documentary research deals with the influences of Orthodox iconography, folkloric art, and occidental modernist tendencies on the Russian avant-garde palette; and is studying the effects of contradictory historical processes in the chromatic profile of individual paintings. In the experimental section a series of colorants are investigated concerning the effects of accelerated ageing on experimental painting tables, prepared as watercolour and gouache layers on paper ground. The resulting samples are subject to colorimetric, and spectroscopic measurements; and analogous analytical procedures are applied on samples taken from selected paintings belonging to the Costakis Collection. A systematic comparative study of all data permits evaluating the materials used as to their stability towards exstrincic factors, and proposing degradation routes, in order to assist museum curators and conservators in every concrete case related to the broad spectrum of pigments examined.     

Insight into framework destruction in ultramarine pigments

We report key evidence on the framework destruction in ultramarine pigments upon color fading. Experiments on faded pigments in a fresco painting environment reveal that the paramagnetic chromophores are set free via sodalite framework destruction and are subsequently degraded. Fading in acidic media produces similar results, although a larger number of beta-cages appear to be destroyed, and H2S is released. The findings are further supported by studies on natural and synthetic ultramarine pigments of various shades via solid-state resonance-Raman spectroscopy, colorimentry, and solid-state 29Si and 27Al NMR spectroscopy. NMR parameters are shown to correlate well with the intensities of Raman signals corresponding to the S3(-*) chromophores. A further correlation is established between the colorimetric parameters, L* (lightness) and C* (chroma), and the paramagnetic shift and paramagnetic linebroadening in NMR spectra for both 27Al and 29Si.     

The identification of synthetic organic pigments in modern paints and modern paintings using pyrolysis-gas chromatography-mass spectrometry

A collection of more than 70 synthetic organic pigments were analysed using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). We report on the analysis of diketo-pyrrolo-pyrrole, isoindolinone and perylene pigments which are classes not previously reported as being analysed by this technique. We also report on a number of azo pigments (2-naphthol, naphthol AS, arylide, diarylide, benzimidazolone and disazo condensation pigments) and phthalocyanine pigments, the Py-GC-MS analysis of which has not been previously reported. The members of each class were found to fragment in a consistent way and the pyrolysis products are reported. The technique was successfully applied to the analysis of paints used by the artist Francis Bacon (1909-1992), to simultaneously identify synthetic organic pigments and synthetic binding media in two samples of paint taken from Bacon's studio and micro-samples taken from three of his paintings and one painting attributed to him.     

Byzantine wall paintings from Kastoria, northern Greece: spectroscopic study of pigments and efflorescing salts

This study concerns the investigation of pigments and efflorescence phenomena on the wall paintings of Kastoria, a rural, non-metropolitan Byzantine town. A large number of representative samples were collected from the murals of three churches, dated to post-Byzantine era (14th-17th c. AD). The identified pigments for the red colour were hematite (Fe2O3), cinnabar (HgS) and minium (Pb3O4), while brown and yellow colours were attributed to mixtures of ochres (Fe-oxides and hydroxides) and lime. The utilization of admixtures of iron, lead and mercury compounds was also attested in order to render specific tones on the painted surfaces. Black and dark blue hues were prepared using black carbon and Mn in some cases. Grey colours were assigned to a mixture of black carbon and lime. Green colour is rather attributed to admixtures of Fe-rich minerals and lime and not to the commonly used green earths. Baryte (BaSO4) was also evidenced as a filler or extender. Phosphorous was detected and connected to proteinaceous material and Mo and Sb were traced which are probably affiliated to Fe-oxides. Regarding efflorescing salts, the determined compounds are: calcite, dolomite, gypsum, halite, nitratine, natron and mirabilite, all of which are related to temperature and humidity changes and moisture fluctuations inside the wall paintings.     

Micro-Raman spectroscopic investigation of external wall paintings from St. Dumitru’s Church, Suceava, Romania

The external sixteenth century wall paintings of St. Dumitru's Church in Suceava (Romania) are suffering visually from deterioration. Fragments of these paintings spallated from the external wall have been studied by micro-Raman microscopy in order to elucidate possible causes of this process. Calcite and alpha-quartz are the components of the substratum indicating that the artists used the Roman fresco technique comprising a limewash putty. No organic binders have been detected in the substrate or pigment application. Amorphous carbon and goethite, alpha-FeOOH, have been identified in areas containing residues of grey and yellow pigments, respectively. Small amounts of gypsum have been detected in the grey areas which we attribute to special attention being given to surface preparation and pigment application in these areas. An abundance of sodium nitrate, nitratine, microcrystals have been observed on the surfaces of many fragments which suggests that a biodeterioration process originating from guano deposits could have been operating in these frescoes.     

Monet's painting under the microscope.

An oil painting by Claude Monet, Port-Goulphar, Belle-Ile 1887 (collection of the Art Gallery of New South Wales), was examined to determine both the identity of the pigments used by the artist in this painting and his technique of mixing colors and laying paint on the canvas. The extremely complex construction of the painting was revealed by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), and X-ray mapping (XRM) analysis of cross sections of paint flakes excised from damaged regions of Port-Goulphar, Belle-Ile. Nine different pigments were found on the painting. Many of the identified colors were modern pigments that became available only late in the 19th century as a result of scientific advances in pigment chemistry. Although similar colors were available in a natural mineral form, they lacked the vivid color of their manufactured counterparts. The use of these new synthetic metallic oxide colors by Monet accounts for the brilliance of his paintings. In addition, a separation between successive paint layers was observed in some areas of paint chip cross sections, indicating that oil-based paint was applied to paint that had dried, and consequently, Port-Goulphar, Belle-Ile was painted over a long period of time. This observation is contrary to the general perception of Monet's technique of painting freely and quickly.     

Multivariate chemical mapping of pigments and binders in easel painting cross-sections by micro IR reflection spectroscopy

Paintings are composed of superimposed layers of inorganic and organic materials (pigments and binders). Knowledge of the stratigraphic sequence of these heterogeneous layers is fundamental for understanding the artist’s painting technique and for conservation issues. In this study, micro-IR mapping experiments in reflection mode have been carried out on cross-sections taken from simulations of ancient easel paintings. The objective was to locate both organic binders and inorganic pigments. Chemical maps have been re-constructed using the common approach based on the integration of specific infrared bands. However, owing to the complexity of painting materials, this approach is not always applicable when dealing with broad and superimposed spectral features and with reststrahlen or derivative-like bands resulting from acquisition in reflection mode. To overcome these limitations, principal-component analysis has been successfully used for the re-construction of the image, extracting the relevant information from the complex full spectral data sets and obtaining reliable chemical distributions of the stratigraphy materials. Different pigment–binder combinations have been evaluated in order to understand limitations and strengths of the approach. Finally, the method has been applied for stratigraphic characterization of a cross-section from a 17th century wooden sculpture identifying both the original paint layer and the several overpaintings constituting the complex stratigraphy.     

Thermal,mineralogical and spectroscopic study of plasters from three post-Byzantine churches from Kastoria (northern Greece)

Several plaster samples were collected from the wall paintings of post-Byzantine monuments from Kastoria town, northern Greece. They were analysed mainly by simultaneous thermal analysis (TG-DTG/DTA) and X-ray diffraction and supplementary by electron microscope (ESEM-EDX) and Raman spectroscopy. Whitish and dark plaster layers were evident in most cases. Calcite, micas, and quartz were the dominant minerals, while dolomite, gypsum, and feldspar were detected as minor phases in most of the samples. Hydromagnesite and chlinochlore were also determined in a few samples. The utilisation of the results for chronological purposes (i.e. for assignment of different painting periods) was also suggested and the presence of dolomite and hydromagnesite could be characteristic for the provenance of the raw material. Gypsum was regarded mainly as a weathering product due to sulfation process, and secondly as a binding material of the plaster. The thermoanalytical results are in good agreement with the mineralogical data. The white plasters are categorized as hydraulic lime mortars, while the dark ones as natural pozzolanic mortars. Calcite and gypsum correlates well with their respective mass losses at certain temperature ranges and their Raman spectra are clearly detected. ESEM-EDX revealed fine calcareous components with aluminolisilicate aggregates and the application of the fresco technique either as a multi-layer or a single-layer plaster. The deterioration caused by salts (gypsum, halite, and nitratine) and micro-organisms was also determined. The detrimental effect of the salt crystallization and dissolution was also confirmed using the so-called Peltier-stage experiment.     

Studying pigments on painted plaster in Minoan,Roman and Early Byzantine Crete. A multi-analytical technique approach

Wall paintings spanning two millennia of Cretan painting history and technology were analysed in an effort to determine similarities and evolutions of painting materials and technology. A multi-technique approach was employed that combined the use of (a) laser-induced breakdown spectroscopy (LIBS) and Raman microspectroscopy, based on mobile instrumentation, appropriate for rapid, routine-level object characterization, and (b) non-destructive X-ray diffractometry (XRD), performed directly on the wall painting fragment, which provides detailed information on the minerals constituting the paint. Elemental analysis data obtained through LIBS were compared with molecular and crystal structure information from Raman spectroscopy and XRD. Cross-sections from selected samples were also investigated by means of optical microscopy and scanning electron microscopy coupled to micro-probe analysis and X-ray mapping that enabled identification of several mineral components of the paint confirming the results of the XRD analysis. In parallel, replica wall paintings, created with known pigments and binding media for reference purposes, were examined with optical microscopy and stain tested for organic materials. The overall study shows that the LIBS and Raman techniques offer key advantages, such as instrument mobility and speed of data collection and interpretation that are particularly important when dealing with on-site investigations. Thus, they are capable of providing important compositional information in an effective manner that enables quick surveying of wall paintings and permit targeted sample selection for further analysis by advanced laboratory techniques.     

Spectroscopic analysis of roman wall paintings from Casa del Mitreo in Emerita Augusta, Mérida, Spain

The use of visible spectroscopy, applied to chromatic characterization of Roman wall paintings, allows an easy and trustworthy grouping of the samples studied. The use of other spectroscopic techniques such as Fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDS) in conjunction with X-ray diffraction (XRD) allows a good identification of the substances present in the pictorial layers that define and differentiate each chromatic group. In this paper, a study of 40 Roman wall painting samples, from Pinturas Báquicas of Casa del Mitreo in Emerita Augusta (Mérida, Spain), is described. In these samples, some pigments of high quality and cost, as well as some unusual mixtures, not described in the bibliography, have been found.     

Evolved Gas Analysis‐Mass Spectrometry to Identify the Earliest Organic Binder in Aegean Style Wall Paintings

An organic binder was identified in the painted fragments from the Canaanite palace of Tel Kabri, Israel. Recently dated to the late 18th century B.C.E. by ¹⁴C, Tel Kabri is the most ancient of the Eastern Mediterranean sites in which Aegean style paintings have been found. The application of pigments was suspected to be using an organic binding medium, particularly for the Egyptian Blue pigment. Samples of blue paint were examined using evolved gas analysis‐mass spectrometry (EGA‐MS) in order to overcome the analytical challenges imposed by highly degraded aged proteinaceous materials. Egg was identified as the binder based on the presence of hexadecanonitrile and octadecanonitrile, confirming the use of a secco painting technique. Lysozyme C from Gallus gallus was detected by proteomics analysis, confirming the presence of egg. To our knowledge, this is the earliest use of egg as a binder in Aegean style wall paintings.     

Characterization of pigments and ligands in a wall painting fragment from Liternum archaeological park (Italy)

Spectroscopic and MS techniques were used to characterize the pigments and the composition of polar and nonpolar binders of a stray wall painting fragment from Liternum (Italy) archaeological excavation. X‐ray fluorescence and diffraction analysis of the decorations indicated mainly the presence of calcite, quartz, hematite, cinnabar, and cuprorivaite. Infrared spectroscopy, GC coupled to flame‐ionization detector, and MS analysis of the polar and nonpolar components extracted from paint layers from three different color regions revealed the presence of free amino acids, sugars, and fatty acids. Interestingly, LC‐MS shotgun analysis of the red painting region showed the presence of αS1‐casein of buffalo origin. Compared to our previous results from Pompeii's wall paintings, even though the Liternum painting mixture contained also binders of animal origin, the data strongly suggest that in both cases a tempera painting technique was utilized.     

Analysis of mural paintings in Istria

Fragments of wall paintings from Istria, coming from the Basilica of Guran near Vodnjan, from the cemeterial Church of Saint Simeon in Guran and from the Benedictine monastery of Santa Maria Alta near Bale were studied. The analytical instrumental techniques used were Optical Microscopy, Scanning Electron Microscopy equipped with an EDS microanalysis detector, X Ray diffraction, FTIR infrared Spectroscopy and Raman Spectroscopy. Red and yellow pigments used in Guran and Bale have bean derived from red and yellow istrian bauxites, as already demonstrated for works from 11th to 15th century. The blue pigment found in the paintings of the Bale Chapel is a lapislazzuli blue; this fact confirms the literature data referring to the period from 11th to the 16th century. The materials and pigments used at Bale and Guran fit with the Istrian tradition and history of painting going back to the first Carolingian period.     

Characterization of “oil on copper” paintings by energy dispersive X-ray fluorescence spectrometry

Energy dispersive X-ray fluorescence is a common analytical tool for layer thickness measurements in quality control processes in the coating industry, but there are scarce microanalytical applications in order to ascertain semi-quantitative or quantitative information of painted layers. “Oil on copper” painting becomes a suitable material to be analysed by means of X-ray fluorescence spectrometry, due to the metallic nature of substrate and the possibility of applying layered models as used in coating industry. The aim of this work is to study the suitability of a quantitative energy dispersive X-ray fluorescence methodology for the assessment of the areal distribution of pigments and the characterization of painting methods on such kind of pictorial artworks. The method was calibrated using standard reference materials: dried droplets of monoelemental standard solutions laid on a metallic plate of copper. As an example of application, we estimated pigment mass distribution of two “oil on copper” paintings from the sixteenth and eighteenth centuries. Pictorial layers have been complementarily analysed by X-ray diffraction. Apart of the supporting media made of copper or brass, we could identify two different superimposed layers: (a) a preparation layer mainly composed by white lead and (b) the pictorial layer of variable composition depending on the pigments used by the artist on small areas of the painting surface. The areal mass distribution of the different elements identified in the painting pigments (Ca, Cr, Mn, Fe, Zn, Cd, Hg and Pb) have been determined by elemental mapping of some parts of the artworks.     

Ochre-differentiation through micro-Raman and micro-FTIR spectroscopies: application on wall paintings at Meteora and Mount Athos, Greece

The most widely-used inorganic pigments of Byzantine and post-Byzantine hagiography are earth pigments called ochres such as, red and yellow ochres, limonite, goethite, raw and burnt sienna, caput mortuum and hematite. The present experimental work proposes a technique of differentiation that allows one to distinguish among all the different kinds of iron oxides, thereby providing a better understanding of the painting technique used on portable icons and wall paintings. The ratios between the main spectroscopic peaks, attributable to the major components usually present in ochres, were calculated and compared, one against the another, from the spectra obtained through micro-Raman spectroscopy. Elementary composition is also revealed through a scanning electron microscopy (SEM) analysis. The possibility for detailed study on a particular Byzantine ochre palette can thus be performed based on the small differences in its nature and composition. These differences can first be observed and then measured among all of the natural earth pigments, through microRaman and microFTIR spectroscopies.     

Raman spectroscopic analysis of the Maya wall paintings in Ek'Balam, Mexico

Raman spectroscopy has been applied to the examination of wall painting fragments from the archaeological site of Ek'Balam (Yucatán, Mexico). Thirty-three samples have been studied, all originating from room 23 of the Acropolis, and being representative of the painting technique at Ek'Balam during the late Classic Maya period. Several pigments such as haematite, calcite, carbon, cinnabar and indigo were identified in these samples. The latter pigment was presumed to be present as 'Maya blue', which is an intercalation product of indigo and palygorskite clay. The observed Raman spectra are reported and some band assignments have been made. This survey is the first Raman spectroscopic examination of a whole set of pigments in archaeological Maya wall painting fragments.