A micro-Raman archaeometric approach to Roman wall paintings

Infrared and Raman spectra have been recorded on the surface of plasters from Regium Lepidi (Reggio Emilia, Italy). A palette has been identified, that can be compared with the ones from the nearby towns of the Roman Empire, but some peculiarities can be outlined. Some of the pigments could come from the territory, even though the techniques could be ascribed to those usually present in the 1st century a.c.     

Analysis of Roman wall paintings found in Verona

The present paper deals with the analysis of roman wall paintings fragments recovered from twelve buildings of Verona, Italy. The analytical techniques used were Optical Microscopy, Scanning Electron Microscopy (SEM) equipped with an EDS microanalysis detector, Xray powder diffraction (XRD) Fourier Transform infrared spectroscopy (FTIR) and Raman Spectroscopy. The wall preparation generally consisted of three layer: the pictorial layer, an intonachino layer of hydrated lime and a plaster one made of slaked lime and sand. The pigments found in the studied domus are different reflecting the taste and culture of Xa Regio of Italy but also the economical possibilities of the dominus and the building period.     

Analysis of pigments from Roman wall paintings found in Vicenza

The analysis of about 60 samples of wall paintings was carried out using different chemicophysical techniques: optical microscopy, scanning electron microscopy (SEM) equipped with an EDS microanalysis detector, X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The identified pigments were cinnabar, hematite, red ochre, celadonite, cuprorivaite (Egyptian blue), yellow ochre, goethite and carbon. Only in one case some lead white was found instead. In general, the mortar preparation did not correspond to the complex structure suggested by Vitruvius (De Architectura), but it generally showed a porous layer, with crushed grains under the pigment layer. In certain cases two superposed pigment layers were found: yellow superimposed on both red and pink, black on pink, green on black.     

Analysis of Roman age wall paintings found in Pordenone, Trieste and Montegrotto

The aim of the present work is the study of many fragments of wall painting from archaeological excavations in three different Roman age sites dating back to the I Century before Common Era: Pordenone (località Torre); Trieste (Crosada) and Padova (Montegrotto). The techniques used were optical microscopy, scanning electron microscopy (SEM), equipped with a EDS microanalysis detector, X-rays powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Fourier transform Raman spectroscopy (FT-Raman) and electron paramagnetic resonance (EPR) spectroscopy. The identified pigments were: cinnabar, hematite, celadonite, glauconite, cuprorivaite (Egyptian blue), yellow and red ochre, calcite, limonite, coal black.In general, the mortar preparation did not correspond to the complex procedure suggested by Vitruvius (De Architectura), but generally showed a porous layer, with crushed grains under the pigment layer. In some cases, two superimposed pigment layers were found: yellow superimposed on both red and pink, black on pink, green on black.The slight differences we found in the use of the pigments in the three studied sites might show that the same technology, culture and taste spread all over the Roman Empire in North Eastern Italy (X^a Regio Venetia et Histria).     

Use of different spectroscopic techniques in the analysis of Roman age wall paintings

In this paper the analysis of samples of Roman age wall paintings coming from: Pordenone, Vicenza and Verona is carried out by using three different techniques: energy dispersive x-rays spectroscopy (EDS), x-rays fluorescence (XRF) and proton induced x-rays emission (PIXE). The features of the three spectroscopic techniques in the analysis of samples of archaeological interest are discussed. The studied pigments were: cinnabar, yellow ochre, green earth, Egyptian blue and carbon black.     

Analysis of bulk and inorganic degradation products of stones,mortars and wall paintings by portable Raman microprobe spectroscopy

This work reports the use of a portable Raman microprobe spectrometer for the analysis of bulk and decaying compounds in carbonaceous materials such as stones, mortars and wall paintings. The analysed stones include limestone, dolomite and carbonaceous sandstone, gypsum and calcium oxalate, both mono- and dihydrated, being the main inorganic degradation products detected. Mortars include bulk phases with pure gypsum, calcite and mixtures of both or with sand, soluble salts being the most important degradation products. The pigments detected in several wall paintings include Prussian blue, iron oxide red, iron oxide yellow, vermilion, carbon black and lead white. Three different decaying processes have been characterised in the mortars of the wall paintings: (a) a massive absorption of nitrates that reacted with calcium carbonate and promoted the unbinding of pigment grains, (b) the formation of black crusts in the vault of the presbytery and (c) the thermodecomposition of pigments due to a fire.     

Isotopic analysis of lead present in the cinnabar of Roman wall paintings from the Xth Regio "(Venetia et Histria)" by ICP-MS

The analysis of Roman wall paintings coming from Verona, Vicenza, Padova, Pordenone and Trieste evidentiated the presence of cinnabar. In this work, the isotopic composition (206)Pb, (207)Pb and (208)Pb of trace of lead present in cinnabar is reported, via ICP-MS measurements. The isotopic ratio values are compared with the values obtained from samples coming from Roman wall paintings of Pompeii and from the mines of Almaden (Spain) Monte Amiata (Grosseto Italy) and Idria (Slovenia). All the isotopic data can be represented by a "field" ranging from Huelva, to Almeria Spanish provinces. This trend could be due to the mixing of cinnabar products treated in Rome.     

Analysis of pigments from Roman wall paintings found in the "agro centuriato" of Julia Concordia (Italy)

The analysis of wall painting fragments recovered in the "agro centuriato" of Julia Concordia has been carried out by using Scanning Electron Microscopy equipped with an EDS microanalysis detector (SEM-EDS), Infrared Spectroscopy (FTIR) and X-Ray powder Diffraction (XRD). The pigments used have been identified and the data obtained suggest the presence of three rustic villas richly decorated also with Egyptian blue. The presence of white of aragonite suggest that these villas were decorated during the Imperial Age, in agreement with the recovery of high quality materials and a bronze statue.     

Identification of complex structures of paintings on canvas by NMR: Correlation between NMR profile and stratigraphy

Paintings on canvas are complex structures created by superimposing layers of different composition. Investigations on the structure of these artworks can provide essential information on their state of conservation, pictorial technique, possible overpaintings, and in planning a proper conservation plan. Standard methods of investigation consist in sampling a limited number of fragments for stratigraphic analyses. Despite the recognized validity of these methods, they are affected by evident limitations. Nuclear magnetic resonance (NMR) profiling, often named NMR stratigraphy, is an NMR relaxometry technique applied by single-sided portable devices developed to overcome the disadvantages of microinvasive stratigraphic analyses. The potential of this approach on artworks, including wall paintings and a few examples of painted canvas, is described in the literature. In this study, NMR profiles of painting on canvas were examined by analyzing transverse relaxation time data by T₂ quasi-continuous distributions and the results compared with standard stratigraphic cross-sections analysis. Combining signal intensity and T₂ quasi-continuous distributions, the identification of textile, preparatory, and paint layers was enhanced. The diction “NMR stratigraphy” for these inhomogeneous layered artworks is also discussed. Indeed, unlike the stratigraphic cross-sections, NMR profiles provide information on a volume (flat slice), rather than on a surface, and the collected signal can derive from nonuniform and partially overlapping layers. This study paves the way for extensive investigations on relaxation time quasi-continuous distributions in various binder/pigment mixtures in order to improve the reliability of NMR profile as an innovative, non–invasive, and nondestructive method for analyzing paintings on canvas.     

Ion chromatography characterization of polysaccharides in ancient wall paintings

Specific programming of automated HPLC systems allows total on-line qualification, validation and stability monitoring using the concept of deferred standards. Setting up such a process for routine analyses in an automated HPLC system requires specific autosampler programming as well as specific monitoring software. With an autosampler, a double injection procedure is programmed, the first introducing the sample, and the second, a few minutes deferred, the deferred control standard. Two additional compounds are therefore added to the sample before and during the chromatographic process: the intemal standard for sample quantification and the deferred standard for system control. Specific methodologies are described of how to obtain classical quantitative analysis information as well as system qualification validation stability information. Experiments were performed to develop specified methodologies to monitor the quality of quantitative analysis during the life of the column by using the deferred standard concept to probe the effects of column ageing on separation characteristics.     

Aragonite in Roman wall paintings of the VIII(a) Regio, Aemilia, and X(a) Regio, Venetia et Histria

In the Roman wall paintings different white colours were used, named Paraetonium, Melinum, Anularia, Eretria, Argentaria, etc. FTIR, Raman spectroscopy and X-Ray diffraction were applied to study different white pigments, such as calcite, aragonite, dolomite and huntite, white carbonates present in archaeological findings from Roman walls in the Mediterranean region. This study showed that it is possible to distinguish and identify these components in white colours. About 450 samples of Roman wall paintings were analysed and it was observed that often aragonite is associated to precious coloured pigments. On the basis of the obtained results some considerations about the period in which the different kinds of white pigments were used are proposed.     

How mobile NMR can help with the conservation of paintings

The conservation of paintings is fundamental to ensure that future generations will have access to the ideas of the grand masters who created these art pieces. Many factors, such as humidity, temperature, light, and pollutants, pose a risk to the conservation of paintings. To help with painting conservation, it is essential to be able to noninvasively study how these factors affect paintings and to develop methods to investigate their effects on painting degradation. Hence, the use of mobile nuclear magnetic resonance (NMR) as a method of investigation of paintings is gaining increased attention in the world of Heritage Science. In this mini-review, we discuss how this method was used to better understand the stratigraphy of paintings and the effect different factors have on the painting integrity, to analyze the different cleaning techniques suitable for painting conservation, and to show how mobile NMR can be used to identify forgeries. It is also important to keep in mind its limitations and build upon this information to optimize it to extend its applicability to the study of paintings and other precious objects of cultural heritage.     

Sulfur isotope analysis of cinnabar from Roman wall paintings by elemental analysis/isotope ratio mass spectrometry – tracking the origin of archaeological red pigments and their authenticity

The most valuable pigment of the Roman wall paintings was the red color obtained from powdered cinnabar (Minium Cinnabaris pigment), the red mercury sulfide (HgS), which was brought from mercury (Hg) deposits in the Roman Empire. To address the question of whether sulfur isotope signatures can serve as a rapid method to establish the provenance of the red pigment in Roman frescoes, we have measured the sulfur isotope composition (δ³⁴S value in ‰ VCDT) in samples of wall painting from the Roman city Aventicum (Avenches, Vaud, Switzerland) and compared them with values from cinnabar from European mercury deposits (Almadén in Spain, Idria in Slovenia, Monte Amiata in Italy, Moschellandsberg in Germany, and Genepy in France). Our study shows that the δ³⁴S values of cinnabar from the studied Roman wall paintings fall within or near to the composition of Almadén cinnabar; thus, the provenance of the raw material may be deduced. This approach may provide information on provenance and authenticity in archaeological, restoration and forensic studies of Roman and Greek frescoes. Copyright © 2010 John Wiley & Sons, Ltd.     

Non-destructive in situ determination of pigments in 15th century wall paintings by Raman microscopy

Raman microscopy has been applied to the study of 15th century wall paintings in a chapel of St. Orso Priory palace (Aosta, Italy) in view of their restoration. The use of a transportable instrument has made it possible to work non-destructively in situ without sampling. The main inorganic pigments used by the unknown artist, namely mercury sulphide, azurite, white lead, red and yellow ochre, carbon black and lead tin yellow type I have been identified, and the presence of organic substances and of some decay products (calcium sulphate and oxalate) has been observed.     

The degradation of wall paintings and stone: Specific ion effects

Salts are ubiquitous both on the surface and in the porous network of works of art such as wall paintings and stone. Cyclic solubilization and crystallization takes place with fluctuating environmental conditions, inducing mechanical stress in the pores and the flaking of the artistic surface. The preventive conservation of precious cultural heritage would thus benefit from models able to describe quantitatively the behavior of electrolyte solutions. Besides the pore size distribution of the wall, cyclic crystallization depends on relative humidity and temperature. Whereas the behavior of single salts' solutions is known, that of mixed solutions (commonly found on artifacts) is still an open issue, owing to the specific interactions of counterions and coions. Classical theories of electrolytes need many fitting parameters to provide predictive and quantitative information, and research focuses on matching phenomenological set of rules with models that take into account quantum mechanical dispersion forces. Classical models have been used so far to describe the behavior of some mixed salts' solutions commonly found on murals and stone, in terms of their RH_eq, which is the relative humidity of air in equilibrium with the saturated solution. Results indicate that environmental conditions deemed safe in the presence of single salts, represent indeed a threat to artifacts in the presence of mixed solutions, with other deviations due to the fact that the crystallization of salts takes place within mesoporous networks. We hope that the reviewed results might contribute a stimulus for further reanalysis of the degradation of works of art, where the synergistic effect of counterions and coions are taken into account. Such interpretation of the artifacts' degradation has been so far overlooked in preservation studies.     

Analysis of egg-based model wall paintings by use of an innovative combined dot-ELISA and UPLC-based approach

The chemical analysis of egg-based wall paintings—the mezzo fresco technique—is an interesting topic in the characterisation of organic binders. A revised procedure for a dot-enzyme-linked immunosorbent assay (dot-ELISA) able to detect protein components of egg-based wall paintings is reported. In the new dot-ELISA procedure we succeeded in maximizing the staining colour by adjusting the temperature during the staining reaction. Quantification of the colour intensity by visible reflectance spectroscopy resulted in a straight line plot of protein concentration against reflectance in the wavelength range 380–780 nm. The modified dot-ELISA procedure is proposed as a semi-quantitative analytical method for characterisation of protein binders in egg-based paintings. To evaluate its performance, the method was first applied to standard samples (ovalbumin, whole egg, egg white), then to model specimens, and finally to real samples (Giotto’s wall paintings). Moreover, amino acid analysis performed by innovative ultra-performance liquid chromatography was applied both to standards and to model samples and the results were compared with those from the dot-ELISA tests. In particular, after protein hydrolysis (24 h, 114 °C, 6 mol L^?1 HCl) of the samples, amino acid derivatization by use of 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate enabled reproducible analysis of amino acids. This UPLC amino acid analysis was rapid and reproducible and was applied for the first time to egg-based paintings. Because the painting technique involved the use of egg-based tempera on fresh lime-based mortar, the study enabled investigation of the effect of the alkaline environment on egg-protein detection by both methods.

Deuterium incorporation in biomass cell wall components by NMR analysis

A commercially available deuterated kale sample was analyzed for deuterium incorporation by ionic liquid solution (2)H and (1)H nuclear magnetic resonance (NMR). This protocol was found to effectively measure the percent deuterium incorporation at 33%, comparable to the 31% value determined by combustion. The solution NMR technique also suggested by a qualitative analysis that deuterium is preferentially incorporated into the carbohydrate components of the kale sample.     

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.     

Collagen-protein interactions mapped by phototriggered thiol introduction

Accumulating evidence shows that collagen plays important roles in many biological systems by interacting with various proteins. The major limitation to determining protein-binding sites on collagen has been a lack of useful methods. We have developed a new strategy for mapping these sites using a photoreactive cross-linker, APDP. A unique -SH group can be introduced into collagen in the vicinity of the protein-binding sites by DTT reduction of the SS bond in the cross-linked product. To identify the sites of cross-linking in collagen, the strategy used was as follows: (i) derivatization of the free -SH group with fluorescein-5-maleimide (FM); (ii) fragmentation of collagen with an appropriate collagenase; (iii) separation of FM-labeled fragments by two-dimensional diagonal electrophoresis; and (iv) detection of cross-linked partners of collagen-binding protein as fluorescent spots under UV light. This strategy can be used to determine the binding sites of various proteins on collagen.