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.     

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.     

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.     

陶寺、尉迟寺白灰面的测试研究

在XRD和拉曼光谱分析的基础上,借助XRF、ICP-AES和ICP-MS技术,对取自陶寺、尉迟寺遗址的“白灰面”做了相关测试和研究。结果表明,尉迟寺F85号红烧土房墙体表面白灰面为碳酸钙。陶寺“白灰面”有两种,一种为人工烧制的石灰,系石灰石烧制而成,表面打磨得较为光滑,并且有一块样品分4次加工,分为4层,表层主要为方解石和文石,里层则为石英含量略高的粘土和石灰的混合物,具较高的工艺,另外,有一块“白灰面”经检测为二水硫酸钙,这首次表明我国古代先民在4千年前已经开始开采和使用石膏做为建筑材料。     

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.     

Analysis of artist’s palette on a 16th century wood panel painting by portable and laboratory Raman instruments

Non-destructive analysis of the artist’s palette of ancient wooden panel paintings is a difficult task and studies are rare. Here we compare different methods of analysis of a wooden panel painting, dated to the early sixteenth century, mainly by Raman and infrared spectroscopies. Raman spectra were recorded on collected/sampled micrometric fragments using portable Raman instruments with laser excitation lines at 532 and 785 nm and transportable Raman instruments at 532, 633 and 785 nm; a fixed 1064 nm Raman spectrometer was also used. Infrared analyses were performed in Attenuated Total Reflection (ATR-FTIR) mode. Using the portable instrument, the Raman spectra evidenced white lead, calcite and vermilion only. Raman spectra recorded by transportable and fixed instruments enabled the identification of most of the artist’s palette: (i) white lead, calcite, gypsum and cerussite for white colour; (ii) vermilion, red lead, litharge, haematite for red; (iii) azurite, indigo and lapis lazuli for blue. IR spectra gave information on the organic binding media. XRF analysis on a brown pigment suggested an heterogeneous mixture of a red pigment (such as haematite and/or minium) and a green one as malachite. GC-MS analysis allowed identifying terpenic resin in the composition of the outer protective layer.     

TG-DTA and FTIR analyses of plasters from byzantine monuments in Balkan region

Historic plasters from wall paintings of Byzantine and post-Byzantine churches situated in the Balkan region were studied. All wall paintings were made with fresco technique and are dated from IX - XVI century. Plaster samples were followed from room temperature to 1000°C by Thermogravimetric (TG) and Differential Thermal Analysis (DTA), and one or two significant temperature regions, corresponding to thermal decomposition mechanisms were observed. The analysis of the plaster samples and the composition characterization was carried out using also, Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Although the main components are calcite and quartz (from sand) in different proportions, there are differences between them such as the presence of gypsum being either as a constituent element or due to environmental pollution. The results are examined comparatively taking into account the creation time and place of the paintings.     

Chromatographic,Microscopic, and Spectroscopic Characterization of a Wooden Architectural Painting from the Summer Palace,Beijing, China

The wooden construction painting is a type of an ancient decorative art on Chinese ancient structures. Comprehensive reports concerning the composition of these materials are rather limited. Here multiple analytical methods were applied to systematically explore the morphology and materials. Several paintings were characterized using a morphological microscope. Scanning electron microscopy–energy dispersive spectrometry (SEM-EDS), X-ray fluorescence (XRF), and X-ray diffraction (XRD) detected emerald green and ultramarine in the paint layers. Gas chromatography–mass spectrometry (GC-MS) indicated that the binding medium in the first layer was composed of blood. Our study helps to comprehensively understand the preparation of the wooden construction paintings in the renowned Summer Palace and provide a scientific basis for its restoration and related archeology work.     

In situ analysis of mediaeval wall paintings: a challenge for mobile Raman spectroscopy

Raman spectroscopy is an analytical technique, which is gaining attention as a molecular technique for the investigation of objects of art. Especially the non-destructive properties of the method make this application suitable for the in situ analysis of artefacts. However, although using mobile, fibre optics Raman instrumentation for this type of research seems to be straightforward, some practical obstacles may hamper the investigation. In this paper, pitfalls and solutions are described when applying a dedicated spectrometer to the analysis of mediaeval wall paintings. It is shown how some practical problems may be overcome, and the results of the analysis are presented. Although the mediaeval wall paintings from the chapel of the castle of Ponthoz are well-preserved, still some interesting degradation phenomena could be observed: the identification of a black degradation product, likely to be meta-cinnabar, a degradation product of the red pigment vermilion (HgS); the formation of gypsum (CaSO₄·2H₂O) as a weathering product of calcium carbonate (CaCO₃); the observation of copper(II)hydroxychlorides.     

Use of in situ and confocal Raman spectroscopy to study the nature and distribution of carotenoids in brown patinas from a deteriorated wall painting in Marcus Lucretius House (Pompeii)

Colonisation of wall paintings by microorganisms and other organisms is a well-known problematic phenomenon. Besides taxonomic identification of the biodeteriogen, it is essential to evaluate the consequences of the colonisation, e.g., unsightly coloured patinas. This work proposes new methodology for characterisation of the nature of the main carotenoids and their distribution in brown stains or patinas of a deteriorated wall painting on the north wall of the atrium of Marcus Lucretius House (Pompeii, Italy). Characterisation of the brown patinas and surrounding areas (plaster and polychromy) from the wall painting started with in situ screening using, mainly, a portable Raman instrument with a handheld FTIR (DRIFTS sampling interface) in order to select the sampling areas suitable for further analysis in the laboratory. Two wall painting fragments were then analysed in the laboratory in two steps. First, microscopic observations (SEM and phase-contrast microscopy) were used to determine whether biodeteriogens were present in the samples. In a second step, confocal Raman microscopy (785 and 514 nm excitation lasers) was used to characterise the main biogenic compounds of the brown stains. Because of the resonance Raman effect (514 nm excitation laser), it was possible to obtain reliable Raman features to assign not only the nature of the main biogenic pigments (carotenoids) present in the stains, but also their spatial conformation. Moreover, Raman confocal applications, for example, Raman imaging and depth profiling were also used in a first attempt to determine the distribution of biosynthesised carotenoids in the stains, and to determine the thickness of the brown patinas.     

A Silver Monochrome “Concetto spaziale” by Lucio Fontana: A Spectroscopic Non- and Micro-Invasive Investigation of Materials

In several of his artworks, for instance the Venezie cycle, Fontana employed metallic paints; previous investigations on such materials highlighted the use of different synthetic binders and of thick paint layers below the metal one, having different colours to change the visual perception of the metallic surface. In the present work, a monochrome silver “Concetto spaziale” by the Italo–Argentine artist belonging to a private collection recently gifted to the museum of the Church of San Fedele in Milano, Italy, was investigated to deepen the knowledge of this particular group of Fontana’s paintings. The artwork was initially visually inspected in visible and ultraviolet (UV) light. Subsequently, a non-invasive spectroscopic investigation was performed by X-ray fluorescence (XRF), reflection Fourier-transform infrared (FTIR) and Raman spectroscopy. A minute fragment of silver-coloured paint was taken from the reverse of the painting, near the cut edge, and examined by scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX) and micro-Fourier-transform Raman (FT-Raman) spectroscopy. The analytical data made it possible to identify the composition of the metallic paint layer and of the underlying dark one, both from the point of view of the pigments and of the binders used, also highlighting the potential of the non-invasive and micro-invasive methods adopted in the investigation.     

Studies of wall painting fragments from Kaiping Diaolou by SEM/EDX, micro Raman and FT-IR spectroscopy

The multi-technique analytical approach has proved to be a very effective tool for the analysis of artwork, as demonstrated by various studies. In this work, four micro-analysis methods were used to analyze the wall painting fragments in Kaiping Diaolou, a world cultural heritage enlisted in 2007. Field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray micro-analysis (EDX), combined with micro Raman and Fourier transform infrared (FT-IR) spectroscopy, provided a vast amount of information concerning the raw materials present in the pigments, organic binder, plasters and mortars of the wall painting. Four types of pigments (goethite, lazurite, chromium green and calcite) were identified on the surface layer of the wall paintings. The substrate under the pigment layer was found to be composed of cubic-like calcite (CaCO₃), micro-rod bundle-shaped syngenite (K₂Ca(SO₄)₂·H₂O), gypsum (CaSO₄·2H₂O) and silica (SiO₂). The organic binder can be attributed to animal glue (such as egg) and drying oil by micro FT-IR spectroscopy. These analysis results can provide important information for the conservation and restoration of the Kaiping Diaolou.     

In situ investigations of vault paintings in the Antwerp cathedral

X-ray fluorescence spectroscopy (XRF) and Raman spectroscopy have been used to examine 15th century mediaeval and 16th century renaissance vault paintings in the Our Lady's Cathedral (Antwerp, Belgium) in view of their restoration. The use of mobile instruments made it possible to work totally non-destructively. This complementary approach yields information on the elemental (XRF) and on the molecular composition (Raman) of the pigments. For the 15th century vault painting the pigments lead–tin yellow (Pb₂SnO₄), lead white (2PbCO₃·Pb(OH)₂), vermilion (HgS), massicot (PbO) and azurite (2CuCO₃·Cu(OH)₂) could be identified. The pigments used for the 16th century vault painting could be identified as red lead (Pb₃O₄), hematite (Fe₂O₃), lead white (2PbCO₃·Pb(OH)₂) and azurite (2CuCO₃·Cu(OH)₂). For both paintings the presence of the strong Raman scatterer calcite (CaCO₃) resulted in a difficult identification of the pigments by Raman spectroscopy. The presence of gypsum (CaSO₄·2H₂O) on the mediaeval vault painting probably indicates that degradation took place.     

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.     

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.     

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.     

Noninvasive and nondestructive NMR, Raman and XRF analysis of a Blaeu coloured map from the seventeenth century

A complete multianalytical study of a hand-coloured map from the seventeenth century is presented. The pigments atacamite, massicot, minium, gypsum, carbon black and vermilion were determined by means of XRF and Raman spectroscopy. The state of conservation of the cellulosic support was monitored by means of unilateral NMR. The analysis was nondestructive and noninvasive, and thus several spectra were collected from the same areas, yielding more reliable results without damaging the artwork. The role of copper pigments in the oxidation processes observed in the cellulosic support is discussed, as well as the possible provenance of atacamite as a raw material instead of as a degradation product of malachite.     

Ancient Roman wall paintings mapped nondestructively by portable NMR

The stratigraphies of decorated walls in ancient Herculaneum, Italy, were analyzed by single-sided ¹H NMR. A large version of the NMR-MOUSE® with a maximum penetration depth of 25 mm was used to map proton density profiles at different positions of the Mosaic of Neptune and Amphitrite showing considerable differences between different tesserae and the mortar bed at different times of the year. In the House of the Black Room, different mortar layers were observed on painted walls as well as different proton content in different areas due to different moisture levels and different conservation treatments. The proton density profiles of the differently treated areas indicated that one method leads to higher moisture content than the other. Untreated wall paintings from different times were profiled in a recently excavated room at the Villa of the Papyri showing two different types of mortar layer structures which identify two different techniques of preparing the walls for painting. Reflectance Fourier mid-infrared spectroscopy and in situ X-ray fluorescence measurements complemented the NMR measurements and provided additional insight into the identification of organic coatings as well as the nature of the pigments used, respectively. The information acquired nondestructively by NMR is valued for elaborating conservation strategies and for identifying different schools of craftsmen who prepared the mortar supports of the wall paintings.     

Raman spectroscopic study of a post-medieval wall painting in need of conservation

Raman spectroscopic studies of four specimens from an important angel wall painting in need of conservation work in a medieval church have provided some information about the pigments and pigment compositions which will influence possible future preservation and restoration strategies. Excitation of the Raman spectra at 1,064 nm in macroscopic mode and at 785 nm in microscopic mode revealed that the white pigment on the angel's wings was a mixture of barytes with calcite and lead white in minor composition. Although the specimens provided were not directly associated with coloured regions of the painting, yellow and blue microcrystals were found and they were identified as chrome yellow and lazurite, respectively. Red and brown particles were identified as cinnabar/vermilion and haematite. Several green particles were also found but could not be identified. The green and blue crystals could be related to neighbouring coloured regions of the artwork and the yellow colour could be identified as a background to the angel figure. Particles of carbon were found to be dispersed throughout the specimens and can be ascribed to soot from candles, heating stoves or oil lamps providing lighting in the church. No evidence for biological deterioration was found from the spectra. The unusual pigment palette is strongly suggestive of a later date of painting than was originally believed but there is a possibility that an earlier rendition exists underneath. Following a review of the spectroscopic data, a more extensive sampling protocol is recommended, from which some stratigraphic evidence could identify the underlying plaster and possible artwork.     

An advanced multivariate approach for processing X-ray fluorescence spectral and hyperspectral data from non-invasive in situ analyses on painted surfaces

In the last decades, in situ non-invasive analytical techniques have been widely used for the analysis of paintings. These techniques are useful to extensively map the surface in a non-invasive way, in order to identify the most representative areas to be sampled. When spectroscopic investigations, such as X ray fluorescence (XRF), are conducted, they usually imply the acquisition of a huge amount of measurements. Subsequently, all these data should be processed in situ, in order to immediately support the sampling strategies. To this aim, an appropriate and fast strategy for multivariate treatment of XRF spectral and hyperspectral data sets is presented, able to account for inter-correlation among variables, which is an issue of high importance for elemental analyses. The main advantage of the approach is that XRF spectral profiles are analysed directly, without computation of derived parameters, by means of principal component analysis (PCA). This procedure allows a fast interpretation of results that can be accomplished in situ. Particular attention was paid to the selection of proper spectral pre-treatments to be applied on data together with the use of several chemometric tools (peak alignment, spectra normalisation and exploratory analysis) aimed at improving the interpretation of XRF results. In addition, the application of multivariate exploratory analysis on XRF hyperspectral maps was studied by using an interactive brushing procedure. The multivariate approach was validated on data obtained from the analysis of the famous Renaissance panel painting “The Ideal City”, exhibited in Palazzo Ducale of Urbino, Italy.