Microscopic, mass spectrometric and spectroscopic characterisation of the mordants used for gilding on wall paintings from three post-Byzantine monasteries in Thessalia, Greece

The main churches of three monasteries in Thessalia, Central Greece are decorated with wall paintings from the post-Byzantine period. The main goal of the present study is to offer insights into the decorative technique of mordant gilding, especially the chemical composition of the mordants and the effects on them of ageing. Light microscopic (LM) examination was carried out on samples taken from the gilded areas of the paintings to view their layer build-up. Direct temperature resolved mass spectrometry (DTMS) under electron ionisation (EI) and chemical ionisation (CI) conditions led to the identification mainly of the organic, as well as some inorganic compounds. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) gave an account of the elemental composition on selected cases. The results from samples taken from different wall paintings were compared with each other to observe their differences and similarities. Furthermore, the three churches in question are believed to have been painted by the same painter, who has only been identified in one of them. Hence, the comparison of the wall paintings as far as the mordant gilding technique is concerned provided additional evidence on the identity of the painter in the other two churches.     

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.

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.     

Byzantine wall paintings from Mani (Greece): microanalytical investigation of pigments and plasters

The present case study concerns the technology of Byzantine wall paintings from the Mani Peninsula, Greece. An assemblage of 12 Byzantine churches, constructed in the tenth to fifteenth century, was included in an initial analytical survey. Two random samples of wall paintings were taken in each monument in order to study their micro stratigraphy and the composition of pigment and plaster layers. Polished sections were fabricated for examination with optical microscopy and scanning electron microscopy (SEM). Furthermore, selected samples were powdered and analysed with Fourier-transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The analytical results achieved in this case study provided general conclusions concerning painting techniques for wall paintings in a rather provincial area of the Byzantine Empire. The palette comprised mainly earthen pigments like ochres and carbon black but occasionally also other pigments like cinnabar, minium and ultramarine. In view of future studies, a portable X-ray fluorescence analysis (XRF) set-up was tested.     

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.     

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.     

Stratigraphic analysis of organic materials in wall painting samples using micro-FTIR attenuated total reflectance and a novel sample preparation technique

Wall paintings typically contain low concentrations of organic materials within a largely inorganic matrix and are characterised by their high porosity and long-term exposure to severe environmental conditions. The identification of organic materials within specific paint or plaster layers is challenging and the inherent characteristics of wall painting samples present further complications. Embedding materials (such as epoxy, polyester and acrylic-based resins) used to produce cross-sections often infiltrate porous and leanly bound samples, and compromise the interpretation of Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectra and the qualitative identification of natural organic materials. An alternative method for the preparation of cross-sections of wall painting samples was developed using cyclododecane (C(12)H(24)) as a temporary consolidant and barrier coating to encapsulate the sample, and to provide necessary support to produce a cross-section through microtoming. Impacts of traditional and novel sample preparation techniques on the identification of organic materials with micro-FTIR-ATR were examined for both replica and real wall painting samples.     

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 wall paintings in the Oratorio of San Giovanni Battista in Urbino: a study finalized to a correct conservation project

The walls of the Oratorio of San Giovanni Battista in Urbino are decorated with outstanding mural paintings dating back to the 15th century. Due to degradation processes that have occurred in the past years, such paintings require a conservative restoration project. In order to evaluate reasons of the decay, some scientific studies have been performed. They consist of macroscopic observations and chemical (EDS), morphological (SEM) and mineralogical (XRD) analyses of samples both from the original preparatory layers under the painted layers and from the restored plasters at the surbase of the wall. In addition, environmental studies have been performed to verify microclimatic conditions of the church in which the mural paintings are located. Finally, a conservative restoration project was proposed.     

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.     

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.     

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.     

GC-MS characterisation and identification of natural terpenic resins employed in works of art

Natural resins were frequently employed in the past as adhesives or as components of oleo-resinous media in paintings. The identification of vegetable resins is still an open problem. The aim of this paper is to analyse by GC-MS some vegetable resins frequently employed in paintings, such as Venice turpentine, dammar, copal, elemi, in order to identify their main components in samples both raw and aged. Some molecules are proposed as chemical markers to identify these natural resins. Two samples scraped off from XV and XVII century paintings were used to test the reliability of proposed method.     

Gas chromatography/mass spectrometry of oils and oil binders in paintings

A GC/MS procedure has been developed, optimized, and applied to characterization of oil binders in paintings. The procedure involves hydrolysis of lipids to fatty acids (FAs) and derivatization of FAs to fatty acid methyl esters (FAMEs) by a solution of sodium methanolate in methanol at an elevated temperature. FAMEs are analyzed by temperature-programed GC followed by full-scan MS. Old and dried samples are subjected to extraction of nonpolymerized FAMEs into dichloromethane prior to hydrolysis. The method provides a good repeatability of results and has been applied to the characterization of common plant oils used in paintings, to commercial oil and tempera paints, to model painting samples, and to samples taken from real paintings. The fresh oils and binders can readily be identified and characterized. The ratio of the methyl esters of palmitic and stearic acids can be used to characterize oil binders in old works of art.     

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.     

Minerals associated with artists’ paintings and archaeological iron objects

This article provides a short review of mineral-based pigments used in paintings with examples drawn from technical studies of selected historic paintings. Pigments such as azurite, natural ultramarine, orpiment, and clay earth pigments have been identified. Some examples will also be given of particular case studies which describe the alteration of selected pigments and consequences of these interactions. The second theme shows how use has been made of such interactions in evaluating the effects of environmental impact on paintings and reference is made to previous studies and the application of paint films as dosimeters. Accelerated ageing and site exposure studies are reported, and results provide information on pigment binder interactions. Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TG) have been used to characterise the behaviour of pigments in binding media and to assist in characterising samples from wall paintings. Reference is also made to the occurrence of iron-oxide based minerals present as corrosion products in archaeological iron objects. Examples are given of objects from two archaeological sites in England, the Anglo-Saxon burial site Sutton Hoo in Suffolk, and the burial site in Wetwang, East Yorkshire. It will be shown that post excavation changes occur in the objects and this information is used to inform preventive conservation of these objects, in storage and in display.     

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.     

Identification of proteinaceous binding media of easel paintings by gas chromatography of the amino acid derivatives after catalytic hydrolysis by a protonated cation exchanger

Summary A procedure for the hydrolysis of proteins, based on catalysis by the protonated form of a strong cation exchanger, was established for proteinaceous binding media (e.g. casein, egg, animal collagene) used for objects of art. The experimental parameters for the hydrolysis (temperature, time) were optimized, as well as the conditions for sorption and desorption of the amino acids on the cation exchanger. The results for the identification of proteins by the gas chromatographic pattern of the amino acid derivatives, after hydrolysis by the ion exchanger and by hydrochloric acid were compared. The former method proved to be more efficient due to the mild conditions, avoiding the formation of humins in the presence of carbohydrates, and reducing the dissolution of pigments. The method was applied to identify the proteinaceous vehicles of samples from priming and paint layers of easel and wall paintings from the 16th and 18th century.     

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.     

Environmental Research for Art Conservation and Assessment of Indoor Conditions Surrounding Cultural Objects

This paper describes the results and conclusions of research directed towards the development and evaluation of a chemical sensor which would provide information on the quality of indoor environments surrounding cultural objects. In our case these objects were paintings housed in major European galleries and the main objective is their preservation through an improved understanding of their microenvironment. The concept was to prepare and expose test tempera paintings which would behave as dosimeters and integrate the environmental response at these locations. Artificial ageing of similar samples was performed to provide a means of calibrating the test paintings. Samples from the test paintings were compared with artificially aged samples and this enabled the sites to be ranked in terms of their suitability for exposure of cultural objects. Additionally, novel methodology involving piezoelectric sensors was designed for monitoring the relative humidity and temperature of the microenvironment of paintings. Dielectric techniques were also used for measuring the effect of relative humidity fluctuations on artists' materials and novel non-invasive dielectric techniques in the microwave region were used for the determination of their moisture content. This revised version was published online in August 2006 with corrections to the Cover Date.