Pigments In Wall Paintings Research Articles

Digital image-based method to identify historical pigments in wall paintings

In this paper, a new analytical approach based on smartphone digital-images analysis coupled to chemometrics is proposed to investigate the nature of different pigments of historical and cultural interest. To that end, wall painting replicas were prepared and painted with 9 different pigments covering three colors: yellow, blue, and green. The mockups were photographed with a smartphone, and the images calibrated using a reference color chart. Two approaches were tested: one based on commercial color charts, and other based on lab-made ad hoc charts. The former demonstrated to yield better results, and the calibrated CIELAB coordinates were used to build Support Vector Machines (SVM) as a classification method. The optimized SVMs were able to successfully classify each pigment based on corrected CIELAB color descriptors, with errors of prediction below 5 %. Overall, this paper proposes a fast and non-invasive analytical method based on image treatment and chemometrics to discriminate among historical pigments in wall painting replicas.

Non-invasive identification of red and yellow oxide and sulfide pigments in wall-paintings with portable ER-FTIR spectroscopy

Scientific interest in analytical tools that enable reliable, repeatable, and rapid measurements without sampling is growing in the field of cultural heritage. Therefore, improving the use of methods that permit an efficient characterization of a wide range of materials through non-invasive and portable instruments, such as spectroscopies, is currently in high demand. This work is focused on the non-invasive study and identification of selected red and yellow pigments containing oxides and sulfides, frequently used in ancient wall-paintings, by means of portable External Reflectance Fourier Transform Infrared spectroscopy (ER-FTIR) within an extended spectral range (7500 - 360 cm−1) which includes a portion of far IR addressing diagnostic peaks and band assignment for the first time. In this work we have also examined the reflection signals of the pigments when applied on a surface representing a fresco wall-painting, to discuss possible changes of the profile as the optical and morphological properties of the surface change.For this purpose, yellow and red oxides, ochres, Siennas, minium, orpiment, and vermillion were selected and used to produce laboratory mock-ups of fresco paints. The ER-FTIR signals obtained on raw pigments were firstly validated by portable non-invasive Raman spectroscopy and X-Ray Fluorescence, and bench-top X-Ray powder Diffraction. Then, the results were subsequently compared with the ER-FTIR signals collected on the mock-ups to discuss the changes in the reflection spectral profile when in presence of rough surfaces and matrix-effects. The combined study on reference materials and mock-ups allowed to identify and discuss ER-FTIR marker bands which were finally validated on real samples of three fragments of Roman frescos provided by the Archeological Museum “San Lorenzo” in Cremona. The proposed method demonstrates distinctive IR features from external reflection analysis on the selected pigments, scarcely studied by portable FTIR instruments, offering a decisive advancement for in situ analytical characterization of the pigments used in wall-paintings.

A Non-Invasive and Sustainable Characterization of Pigments in Wall Paintings: A Library of Apulian Colors

This paper proposed a multianalytical, non-invasive, accessible and expensive (compared to traditional ones) approach for the characterization of pictorial surfaces. A set of 18 pigments and 37 mixtures widely used in the Middle Ages in the Apulia (Italy) artistic and archaeological contexts was considered, and corresponding replicas were produced. Pigments were first characterized by X-ray powder diffraction (XRPD), then replicas were studied by optical microscopy using a portable instrument, colorimetry and fiber optic reflectance spectroscopy (FORS). The investigation provided encouraging results, which allowed the creation of a library including diagnostic microscopic, colorimetric and reflectance markers of each pigment and the identification of the mixtures’ components.

Non-invasive mineral analysis of pigments of wall paintings in the Sungseonjeon Hall

Non-invasive mineral analysis of pigments of wall paintings in the Sungseonjeon Hall

Identification and characterization of basic copper sulfates as mineral green pigments in Andean colonial mural paintings: Use of temperature‐controlled stage for the study of thermal induced antlerite degradation

AbstractThis work describes the characterization of green pigments in wall paintings from the Andean churches of San José de Soracachi and Santiago de Callapa in Bolivia, located on an ancient colonial commercial route known as the Silver Route. To approach our goal, microsamples extracted from the mural paintings and mineral samples, from a mine of the same area, were studied by using micro‐Raman spectroscopy complemented with micro‐energy‐dispersive X‐ray fluorescence spectroscopy (μ‐EDXRF) and scanning electron microscopy with energy‐dispersive X‐ray spectroscopy (SEM‐EDS) analysis. The use of gypsum as the preparation layer was detected, and it suggests a secco painting technique. Antlerite, a basic copper sulfate, was identified suggesting a preference for its use as green pigment in the mural paintings of Andean churches that may be related to the local availability of this mineral. Indeed, this study revealed the presence of heterogeneous particles of the basic copper sulfate together with aluminosilicates, quartz and iron oxides among others, which points to a mineral origin of the green pigment because the same compounds were found in the samples taken in the mine. Because a phase transition has been noticed during the Raman analyses, due to a high power of the laser radiation, some tests have been carried out, varying the laser power, and coupling the Raman spectrometer to a temperature‐controlled stage to verify under which conditions the degradation of the mineral sample of antlerite occurs allowing in this way a correct characterization of basic copper sulfate pigments. These results contribute to the study of the Andean colonial artistic cultural heritage, and this information will be made available for the construction of a database of local pigments of mineral origin used in Andean colonial art.

The combined use of SEM-EDX, Raman, ATR-FTIR and visible reflectance techniques for the characterisation of Roman wall painting pigments from Monte d\u2019Oro area (Rome): an insight into red, yellow and pink shades

The aim of this work has been the identification of the painter’s materials employed in the wall decoration of some destroyed buildings dating approximately between the first century B.C. and the first century A.D. This research originates from a previously started joined archaeological and analytical investigation concerning a varied group of findings that resulted from a rescue excavation performed by Soprintendenza Archeologica in the area of Monte d’Oro in Rome. The focus of this study progression has been directed to a numerous selection of monochrome red, pink and yellow-pigmented fragments. The analyses were performed by means of scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDX) combined with Raman and Fourier transform infrared (FTIR) spectroscopies; visible reflectance measurements have also been carried out and the relevance of this technique in such a kind of archaeological studies has been highlighted. Most attention has been given to the assessment of the performances of non-destructive techniques achieved by portable Raman, and visible reflectance instrumentation to test their diagnostic capabilities. In addition to the expected and well-known pigments such as cinnabar, red ochre, hematite for the reds and yellow ochre for the yellows, the study highlighted a diffuse use of mixed colours and in some cases the possible presence of overlapped painted layers and confirmed the presence of gildings. Among the mixtures of pigments, the most singular outcome concerns the pink fragments revealing the possible application of bone white, which seems to be rather uncommon as a pigment in Roman wall decorations.

Inspecting historical vaulted ceilings by means of physical and chemical analyses: an integrated approach combining active infrared thermography and reflectance spectroscopy

The present study discusses the experimental physicochemical results obtained from the historical vaulted ceilings of an ancient church located in central Italy. Infrared thermography (IRT) in the active configuration was used to map subsurface defects caused by a seismic event and to discover buried structures, while the visible and near-infrared (VIS-NIR) fibre-optics diffuse reflectance spectroscopy (FORS) technique was applied to identify the pigments of wall paintings decorating the vault. Historical photographs are useful to readers in order to clarify the state of conservation before and after the earthquake that took place in 2009. The combination of the experimental results can be useful in restoration processes.

X-Ray Fluorescence Analysis of a Gold Ibex and other Artifacts from Akrotiri

In-situ X-ray fluorescence analysis (XRF) of ancient artifacts from the excavation area was performed using a novel X-ray instrumentation, composed of a portable silicon PIN thermoelectrically cooled X-ray detector, a miniature X-ray source, and portable data acquisition devices. The main objective of the analyses in Akrotiri was to explore the potential of the technique to provide answers to a wide range of archaeometric questions regarding the bulk composition of metal alloys, especially of gold, the characterization of corrosion products in bronze artifacts, identification of inorganic elements which are fingerprints of the minerals used in wall-painting pigments, and of the painting materials and techniques used for the decoration of clay vase surfaces. Among the analysed artifacts are a unique gold ibex, a bronze dagger and blade, various pigments from the wall paintings of room 3 in Xeste 3, decoration pigments from rosettes of faience, a bichrome jug, and other clay vases. The results of the in-situ XRF survey, primarily those of the bulk composition and soldering technology of the gold ibex, are discussed and compared with literature.

Combining multispectral images with X-ray fluorescence to quantify the distribution of pigments in the frigidarium of the Sarno Baths, Pompeii

Abstract Multispectral imaging is used to identify and semi-quantify the distribution of pigments in wall paintings based on mineral-specific band ratios. The western wall in the frigidarium of the Sarno baths in Pompeii was imaged using VIS-IR band-pass filters, stacked as multispectral data, and different pigments were measured using portable X-ray fluorescence (pXRF) and fiber optic reflected spectroscopy (FORS) to determine their chemical composition and spectral signature. Cuprorivaite and hematite were found to be the main minerals in blue and red pigments, with higher amounts of copper and iron respectively. Proportional relations were found between cuprorivaite specific band ratios from multispectral and FORS data and the intensity of copper in pXRF spectra, allowing to map the mineral content on a large scale and determine their relative concentrations. These results were confirmed by X-ray powder diffraction (XRD) and thin section analysis on painted fragments that were detached from the wall paintings and found below. This contribute indicates that on-site portable instrumentation could identify specific pigments and determine their 2D distributions based on non-invasive diagnostics of chemical composition and spectral reflectance in wall paintings.

Graphene‐Enhanced Nanomaterials for Wall Painting Protection

AbstractWall paintings as the highly valuable treasure have been facing severe damaging problems over the years. Ca(OH)2 as a promising material to protect them has been studied for more than a decade. However, the synthesis methods are still costly, complex, and usually, involve an organic solvent. In addition, problems such as large particle size (>150 nm), slow and weak carbonation, and low consolidation strength for wall paintings remain unsolved. This study demonstrates an unprecedented concept of wall painting protection enabled by graphene‐enhanced nanomaterials through strategically synthesizing Ca(OH)2/graphene quantum dot (GQD) nanohybrids using a facile and economic aqueous method. The nanohybrids are uniform and small (center distribution at about 80 nm) and show strong adhesivity to wall painting pigments. In addition, the anti‐UV absorption ability of the nanohybrids is also a significant advantage. More importantly, the Ca(OH)2 is fully carbonated into a stable CaCO3 crystal phase “calcite” because of the GQD, which is crucial in wall painting consolidation. As a result, the graphene‐enhanced nanohybrids show superior conservation efficiency compared to as‐synthesized Ca(OH)2 and commercial Ca(OH)2 materials. The result opens a new direction for protecting cultural heritage using the newly emerging 2D nanomaterials.

In situ X-ray fluorescence-based method to differentiate among red ochre pigments and yellow ochre pigments thermally transformed to red pigments of wall paintings from Pompeii.

Most of the magnificent wall paintings from the ancient city of Pompeii are decorated with red and yellow colors coming from the ochre pigments used. The thermal impact of the pyroclastic flow from the eruption of Vesuvius, in AD 79, promoted the transformation of some yellow painted areas to red. In this work, original red ochre, original yellow ochre, and transformed yellow ochre (nowadays showing a red color) of wall paintings from Pompeian houses (House of Marcus Lucretius and House of Gilded Cupids) were analyzed by means of a handheld energy-dispersive X-ray fluorescence spectrometer to develop a fast method that allows chemical differentiation of the original red ochre and the transformed yellow ochre. Principal component analysis of the multivariate obtained data showed that arsenic is the tracer element to distinguish between both red colored ochres. Moreover, Pompeian raw red and yellow ochre pigments recovered from the burial were analyzed in the laboratory with use of a benchtop energy-dispersive X-ray fluorescence spectrometer to confirm the elemental composition and the conclusions drawn from the in situ analysis according to the yellow ochre pigment transformation in real Pompeian wall paintings.

S.S. Annunziata Church (L’Aquila, Italy) unveiled by non- and micro-destructive testing techniques

The present research work explores the potential of an integrated inspection methodology, combining Non-destructive testing and micro-destructive analytical techniques, for both the structural assessment of the S.S. Annunziata Church located in Roio Colle (L’Aquila, Italy) and the characterization of its wall paintings’ pigments. The study started by applying passive thermal imaging for the structural monitoring of the church before and after the application of a consolidation treatment, while active thermal imaging was further used for assessing this consolidation procedure. After the earthquake of 2009, which seriously damaged the city of L’Aquila and its surroundings, part of the internal plaster fell off revealing the presence of an ancient mural painting that was subsequently investigated by means of a combined analytical approach involving portable VIS–NIR fiber optics diffuse reflectance spectroscopy (FORS) and laboratory methods, such as environmental scanning electron microscopy (ESEM) coupled with energy dispersive X-ray analysis (EDX), and attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR). The results obtained from the thermographic analysis provided information concerning the two different constrictive phases of the Church, enabled the assessment of the consolidation treatment, and contributed to the detection of localized problems mainly related to the rising damp phenomenon and to biological attack. In addition, the results obtained from the combined analytical approach allowed the identification of the wall painting pigments (red and yellow ochre, green earth, and smalt) and provided information on the binding media and the painting technique possibly applied by the artist. From the results of the present study, it is possible to conclude that the joint use of the above stated methods into an integrated methodology can produce the complete set of useful information required for the planning of the Church’s restoration phase.

Raman Identification of Pigments in Wall Paintings of the Colonial Period from Bolivian Churches in the Ruta De La Plata

Micro-Raman spectroscopy was used to analyze and identify pigments and determine the palette of color in wall paintings from four churches of the Colonial Period, in the Bolivian highlands. The ancient churches Santiago de Callapa, Curahuara de Carangas, NuestraSenora de Copacabana de Andamarca and San Jose de Soracachi were constructed during the 17th and 18th centuries, around the important colonial Ruta de la Plata, between Potosi city and Arica harbor on the Pacific coast of South America. Most pigments used in the wall paintings correspond to inorganic minerals as well as to organic colorants. Fully chlorinated copper phthalocyanine (green), copper phthalocyanine (blue), β-naphthol (yellow) and benzoimidazolone (red), were identified in the corresponding colored areas suggesting subsequent recent interventions or restorations. Ground layer materials were also characterized. The present results allow for discussion of the pictorial techniques used in the Andean highland during the colonial period and allow conservators and restorers to make important decisions regarding the type of intervention to perform in the case of these important historical and patrimonial monuments.

Wall painting pigments of Roman Empire age from Syria Palestina province (Israel)

This work is the first step of an extensive project aimed at chemical and mineralogical characterization of pigments of Roman Empire age throughout the provinces. Wall painting materials from two Roman archaeological sites in Israel (the ancient province of Iudaea , later known as Syria Palestina ) were studied: the Roman villa of Lod, dated to the fourth century CE and the synagogue of Migdal, dated between the first century BCE and the second century CE. A total of 165 samples were investigated, producing multi-analytical information from optical microscopy, scanning electron microscopy supported by energy-dispersive X-ray spectroscopy, micro-Raman spectroscopy, X ray diffraction, infra-red spectroscopy, and portable energy-dispersive X-ray fluorescence spectroscopy. This study shows that materials and techniques in the Roman province of Syria Palestina follow Empire tendencies, although advantage was taken also of the local availability of raw materials. Seven different pigments were identified, including Egyptian blue and cinnabar, and the predominant wall painting technique used was fresco occasionally supported by secco retouching.

Wall Paintings from the Roman Emona (Ljubljana, Slovenia): Characterization of Mortar Layers and Pigments

This study concerns the investigation of mortar layers and pigments of wall paintings from the Roman town of Emona (Ljubljana, Slovenia). Fragments of wall paintings consist of up to three preserved mortar layers. The mineralogical–petrographic compositions of the mortars were determined by means of optical microscopy and FT–IR spectroscopy. The investigated samples were divided into several groups based on similar thicknesses of the mortar layer, the binder colour and the composition of an aggregate. Furthermore, the results of mercury intrusion porosimetry showed that mortar layers consisting of carbonate grains exhibited lower porosity with respect to layers with mainly silicate grains, which is attributed to the angular shapes of carbonate aggregate. This is in accordance with the drilling resistance measurement system test (DRMS), confirming that layers with angular carbonate grains are harder than those with addition of rounded silicate ones, due to the good packing effect. The wall paintings were mainly executed using the fresco technique, while for some details secco was used. The identified pigments were red and yellow ochre, green earth, Egyptian blue, carbon black and lime white; all of them belonged to the so‐called austere pigment, which is quite common in Roman wall paintings.

Time-Resolved Photoluminescence Spectroscopy and Imaging: New Approaches to the Analysis of Cultural Heritage and Its Degradation

Applications of time-resolved photoluminescence spectroscopy (TRPL) and fluorescence lifetime imaging (FLIM) to the analysis of cultural heritage are presented. Examples range from historic wall paintings and stone sculptures to 20th century iconic design objects. A detailed description of the instrumentation developed and employed for analysis in the laboratory or in situ is given. Both instruments rely on a pulsed laser source coupled to a gated detection system, but differ in the type of information they provide. Applications of FLIM to the analysis of model samples and for the in-situ monitoring of works of art range from the analysis of organic materials and pigments in wall paintings, the detection of trace organic substances on stone sculptures, to the mapping of luminescence in late 19th century paintings. TRPL and FLIM are employed as sensors for the detection of the degradation of design objects made in plastic. Applications and avenues for future research are suggested.

Identification of pigments on Byzantine wall paintings from Crete (14th century AD) using non-invasive Fiber Optics Diffuse Reflectance Spectroscopy (FORS)

In this paper a combined analytical methodology was employed aiming to explore the potential of the non-invasive Fiber Optics Diffuse Reflectance Spectroscopy (FORS) technique for Byzantine wall painting pigments' characterization, as well as to assess the reliability of analytical information comparing the results with detailed spectral analyses obtained by advanced laboratory techniques such as Environmental Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (ESEM-EDX), Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and micro-Raman Spectroscopy. Byzantine wall paintings (14th Century) decorating two Churches located in the settlements of Patsos and Meronas at Amari, Crete, were investigated in a first systematic research effort to study the mural painting pigments and techniques employed on the island during this period. Micro-sampling was allowed for laboratory analyses only from the Patsos Church's murals. The results obtained from the various spectroscopic methods employed confirmed the identification of pigments (red/yellow ochres, cinnabar, green earth, etc) and that the mixed fresco-secco technique was used in these paintings. In order to characterize the Meronas murals, a comparative study was performed between the acquired FORS spectra of both Churches and the laboratory analyses results. The data obtained confirmed the effectiveness of FORS technique for wall painting pigments' identification, offering key advantages such as instrument mobility and rapid data collection which are of utmost significance in the field of archaeological research.The present work provides detailed information on the structure of pigments and the interpretation of the FTIR spectra by assigning characteristic vibrational modes in these spectra and the electronic transitions of the VIS-NIR spectra, which would be of great value as a reference for other FTIR and FORS researchers in this field.

DETERMINATION OF PIGMENTS AND BINDERS IN POMPEIAN WALL PAINTINGS USING SYNCHROTRON RADIATION – HIGH‐RESOLUTION X‐RAY POWDER DIFFRACTION AND CONVENTIONAL SPECTROSCOPY – CHROMATOGRAPHY

The employment of synchrotron techniques complemented by conventional laboratory systems has allowed us to deepen and improve our knowledge of Roman wall painting procedures. The palette identified in wall paintings from Pompeii and Herculaneum from the second century bc includes goethite, hematite, cinnabar, glauconite, Egyptian blue, and other components such as calcite and aragonite. Proof of the use of organic binders is provided by FTIR and PY–GC/MS. Therefore, the possibility of the use of ‘a secco’ techniques cannot be ruled out. Pigments in wall paintings are usually found in small percentages and conventional X‐ray diffractometers do not detect them. Synchrotron radiation – high‐resolution X‐ray powder diffraction has allowed identification with only a few micrograms of sample.

Educational x-ray experiments and XRF measurements with a portable setup adapted for the characterization of cultural heritage objects

It is common to modify valuable, sophisticated equipment, originally acquired for other purposes, to adapt it for the needs of educational experiments, with great didactic effectiveness. The present project concerns a setup developed from components of a portable system for energy dispersive x-ray fluorescence spectroscopy (EDXRF). Two educational modules have been developed on the basis of this setup. Module 1 comprises a series of x-ray laboratory exercises investigating basic principles, such as the verification of Moseley's law, Compton's law and the Lambert–Beer law. Module 2 concerns the calibration of the XRF with reference materials, aiming to get quantitative measurements of the elemental composition of objects of cultural interest. The application of the calibrated experimental setup is demonstrated with indicative measurements of metal objects and pigments of wall paintings, in order to discuss their spectra, and their qualitative and quantitative analyses. The setup and the applied experiments are designed as an educational package of laboratory exercises on the one hand for students in natural sciences, and on the other for the education of students who will work in the field of cultural heritage, such as conservation science or archaeological science.

An example of the complementarity of laser‐induced breakdown spectroscopy and Raman microscopy for wall painting pigments analysis

AbstractLaser‐induced breakdown spectroscopy (LIBS) and Raman microscopy were used for the identification of pigments in wall painting. Raman spectroscopy, which provides the molecular ‘fingerprint’ of the compound, is nowadays widely used by the archaeometry community, especially for pigment analysis. LIBS, which provides the elementary composition of samples, is a rapid noncontact method, enabling layer‐by‐layer analysis through a precise laser ablation of the sample. This work deals with the behavior of pigments after a LIBS analysis, by trying to identify the compounds before and after the laser shot. Six commercial pigments prepared with the fresco technique were investigated: ultramarine blue, red lead, charcoal, a yellow and a red ochre, and a green earth. Raman spectra, acquired on the sample surface and in the crater induced by LIBS analysis, were compared. The results show that these pigments are well recognized after a LIBS measurement. The analysis of green earth illustrates that the combination of these two techniques gives complete information from a sample. Copyright © 2007 John Wiley & Sons, Ltd.