Analytical study of Roman and Arabic wall paintings in the Patio De Banderas of Reales Alcazares’ Palace using non-destructive XRD/XRF and complementary techniques

A. Duran a , , J.L. Perez-Rodriguez b , M.C. Jimenez de Haro b , M.L. Franquelo b , M.D. Robador c

a Centre de Recherche et de Restauration des Musées de France, Palais du Louvre, 14 quai François Mitterrand, 75001 Paris, France

b Materials Science Institute of Seville (CSIC-University of Seville), Avda Américo Vespucio 49, 41092 Seville, Spain

c Technical Architecture Faculty (University of Seville), Avda Reina Mercedes s/n, 41012 Seville, Spain

Abstract

A portable XRD/XRF system and complementary laboratory techniques were employed to improve the knowledge of the procedures used to create Roman and Arabicwallpaintings. Integrated physico-chemical investigations were conducted on fragments of artworks collected from the archaeological excavation of the PatiodeBanderas in the RealesAlcazares’ Palace of Seville (Spain), and a comparative study on the pigments from both historical periods was performed. As a result, pigments such as vermilion, red ochre, yellow ochre, green earth, Egyptian blue, carbon and phosphor-based black pigments were detected in Roman samples; however, in the Arabic fragments, only haematite was observed. In addition, the size and shape of the particles of the wallpaintings were studied with an XRD 2-dimensional detector and SEM-EDX.

Keywords XRD/XRF portable system; Roman and Arabicwallpaintings; 1st century BC; 11th century AD; RealesAlcazares’ Palace; SEM-EDX

1. Introduction

RealesAlcazares Palace was built by Abd Al-Rahman III, the first caliph of Andalusia, in 913 after a revolt against the government of Cordoba. The palace was built over an ancient Roman settlement outside the city walls of Seville, where the Basilica of St Vicente was located and St Isidoro was buried (Durán-Benito et al., 2007). From 2008 to 2010, an archaeological investigation in the PatiodeBanderas of the RealesAlcazares’ Palace (Fig. 1a) was conducted (Tabales, 2010), and remains of Roman decorated buildings with wallpaintings from the 1st century BC were found. Hispalis (Roman ancient name of Seville) was considered the most important commercial and industrial Hispano-Roman city in the Betic region (Blanco Freijeiro, 1984). The nearby Roman city of Italica, a residential city, is well preserved and provides an impression of the appearance of Hispalis in the later Roman period. During the stratigraphic archaeological investigations carried out in the site, the archaeologists also salvaged Arabic architectural elements and painted decorations from the 11th to the early 13th century. Remains of construction from the 2nd century BC, and the 1st, 3rd, 4th and 5th centuries AD were also discovered; however, wallpaintings were not found (Fig. 1a).

The technique and pigments used by ancient Romans to render and paint walls are of great interest to many researchers. In recent years, numerous studies have been carried out on Romanwallpaintings in Italy, France, England and Spain ( [Delamare, 1983], [Bearat, 1997], [Edreira et al., 2001], [Mazzocchin et al., 2004], [Mazzocchin et al., 2008], [Edwards et al.,

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2009], [Weber et al., 2009], [Aliatis et al., 2010], [Duran et al., 2010a] and [Duran et al., 2010b]). Contemporary written sources ( [Pliny the Elder, 1985] and [Vitruvius, 2005]) provide valuable information on the preparation and application of lime, mortars and pigments, and the fresco paint technique. Coloured pigments were applied when the walls were still damp. In Hispanic monuments with Islamic iconography, evidence of painted fresco decorations has been found (Rallo Gruss, 2003); however, this type of artwork has not been widely studied from a scientific point of view (Cardell et al., 2009). The palette of ornamentation of Islamic buildings is dichromatic (usually red and white), and its design is geometric and repetitive. As a result, this type of ornamentation is a rapid method of decoration (Rallo Gruss, 2003).

In the field of cultural heritage, the objects under study are often precious and unique works of art. Thus, to maintain the artistic value of the work, destructive sampling is minimised ( [Herrera et al., 2009] and [Deneckere et al., 2010]), and non-invasive techniques such as X-rays fluorescence (XRF), μ-Raman or μ-FTIR are often performed ( [De Viguerie et al., 2009], [Kato et al., 2009], [Miliani et al., 2009], [Pinna et al., 2009], [Ricciardi et al., 2009], [Deneckere et al., 2010] and [Nazaroff et al., 2010]). Recently, novel equipment for the in situ analysis of artwork has been developed. In particular, devices that combine two different techniques in the same system have been produced. However, only a few portable X-ray diffraction (XRD) systems for phase identification are currently available ( [Uda et al., 2005], [Chiari, 2008] and [Abe et al., 2009]). XRD requires careful alignment and reproducible incident angles, reflection angles and source-sample-detector distances, etc. Moreover, XRD analyses usually require long acquisition times due to the low intensity of the diffracted beam. Recently, a portable XRD/XRF laboratory equipment has been designed and constructed in the C2RMF (Centre de Recherche et de Restauration des Musées de France) laboratory ( [Gianoncelli et al., 2008], [De Viguerie et al., 2009], [Duran et al., 2010a], [Eveno et al., 2010] and [Pagès-Camagna et al., 2010]). Although the aforementioned device can analyse artefacts in situ, if this cannot be achieved, the object must be transported to the laboratory. Amorphous phases or phases present in very low concentrations are difficult to characterise with the aforementioned techniques. In this case, the combination of energy-dispersive X-rays and scanning electron microscopy provides useful information; however, to apply these techniques, the artefact must be sampled.

The identification and study of pigments used in the Roman and Arabicwallpaintings discovered in the excavations of the RealesAlcazares’ Palace can provide art historians precise information on the techniques used in the creation of the work itself and can provide conservators and restorers with guidelines on the materials necessary for conservation. Integrated physico-chemical investigations were carried out on artwork fragments of the PatiodeBanderas to obtain useful information on the techniques and materials used by the Romans and Arabs. In addition, a comparative study on the pigments from both historical periods was performed. The present paper is one of the first articles devoted to the study of both Roman and Arabicwallpaintings discovered in Seville, and the results of the current investigation were compared to those of similar artworks from the same period found in other locations. To analyse the paintings, a novel XRD/XRF portable system and complementary techniques such as micro-Raman, SEM-EDX and optical microscopy were employed at the Materials Science Institute of Seville and the Centre de Recherche et de Restauration des Musées de France at the Louvre Museum.

2. Experimental

Wallpaintings were discovered in a large Roman building, located in the Republican city of Hispalis and tentatively dated to the 1st century BC. The building was a great structure and

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was built according to the raised skeleton technique, which is characterised by the parallel arrangement of at least three compartmentalised rooms and a corridor with different levels of pavement. Some of the materials were located at a very low level, which could be indicative of a partial basement (Fig. 1a and b) (Tabales, 2010). In the 11th century, after four centuries of Arabic occupation, the Visigothic (post-Roman civilisation) religious complex (Basilica of St Vicente) was destroyed, and a number of buildings and streets belonging to Islamic suburbs were built in the vicinity of the actual catholic Cathedral (approximately 100 m away) (Fig. 1a and c) (Tabales, 2010). The other wallpaintings were found in these Arabic buildings.

The sampling procedure was guided by the location of the paintings within the excavation site and the colours observed on the surface of the paintings. Eight samples from the Roman epoch (1st century BC) and two from the Arabic period (11th century AD) were investigated (Table 1). Because the artefacts were buried, the samples were in excellent condition and were not subjected to any previous restoration processes. The size of the samples was variable (dimensions of 1.0 × 0.8 cm to 8.5 × 6.0 cm), and the thickness of the fragments ranged from 1.0 to 1.5 cm, including the mortar and pictorial layers. Visual examination of the samples indicated that different colours were present in the fragments. Red, yellow, white, green and black colourations were observed in Romanpaintings, and red and white colourations in Arabicpaintings (Table 1). The samples were studied as received (fragments) and as cross-sections.

The portable XRD-XRF apparatus used in the present study is based on a 4-mm beam from a copper anode X-ray source (700 μA and 40 kV), which impinges on the coloured surface of the mural painting fragments at an angle of 10°. Thus, the analysed area was approximately 4 mm × 3 mm (Pagès-Camagna et al., 2010). A 2-dimensional imaging plate detector was used to collect the XRD signal. The diffraction pattern of polycrystalline samples typically consists of concentric Debye-Scherrer rings, which result from the superposition of illuminated crystal oriented in the Bragg condition. The Debye-Scherrer rings contain important information on the micro-structure of the sample, including the grain size, preferential orientation, crystallinity, mosaicity, stress, etc. Spotty rings are produced by coarse-grained mineral phases, and continuous rings are produced by fine-grained mineral phases ( [Rodriguez-Navarro, 2006], [Rodriguez-Navarro et al., 2006] and [Eveno et al., 2010]). Because of the intensity of reflections is more sensitive than the number of reflection spots, the intensity profile of the Debye-Scherrer rings has been used to qualitatively estimate the size of mineral grains. In general, the intensity of the reflections increases on average as with an increase in crystal size, and the number of spots decreases ( [Rodriguez-Navarro, 2006] and [Rodriguez-Navarro et al., 2006]). Other factors that affect the intensity profile of the rings include the structure factor, the reflecting power of the compounds, and the proportion of the different crystalline phases in the samples studied. Free software FIT2D (FIT2D software) was used to transform the 2-dimensional images into standard 1-dimensional XRD diagrams. XRF elemental analysis was performed with a Silicon Drift Detector, whose resolution is of 150 eV FWHM at 5.9 keV and T = −10 °C. The distance from the sample to the detector was set to 2.5 cm, and light elements were not detected due to the strong absorption of air between the specimen and the detector ( [De Viguerie et al., 2009], [Duran et al., 2009], [Duran et al., 2010a] and [Pagès-Camagna et al., 2010]).

A dispersive integrated Horiba Jobin-Yvon LabRam HR800 system was used to perform Raman experiments on the surface of the black fragment. Two external visible diode lasers (solid-state source) are available as excitation lines, including a 532-nm (green) and 785-nm (red) laser; however, the 785-nm laser was mainly used to minimise fluorescence. The apparatus was equipped with a charge-coupled device (CCD) detector and a grating of 600 grooves/nm. An

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optical microscope was coupled confocally to the Raman spectrometer, and the measured area was approximately 25 μm2. The power of the laser ranged from 15 to 50 mW to avoid damaging the painting.

Cross-sections of the samples were obtained from the wallpainting fragments. They were prepared starting from a mould of methyl polymethacrylate where the samples were placed horizontally and refilled up with epoxy resin of methylmethacrylate (Palpress several CE 0044). The resulting material was cut with a fretsaw equipped with a Bahco 302-83S-blade, which was polished with an automatic polishing machine and various grades of sandpaper (grain P-240, P-500, P-800 and P-1200) and was finished with a cloth. The cutting and polishing process was critical for almost all of the samples preparations ( [Duran et al., 2008] and [Duran et al., 2010b]). The cross-sections were examined with optical and scanning electron microscopes. Optical microscopy was performed with a Nikon OPTIPHOT microscope (×25, ×50, ×100 and ×200), and scanning electron microscopy was performed with a HITACHI S-4800 microscope equipped with an energy-dispersive X-ray analyser (EDX) Bruker XFlash 4010 at an accelerating voltage of 20 kV. Samples were coated with gold film prior to the SEM-EDX analyses, and powder samples collected on the surface of the fragments were also studied in some cases. To confirm some of the results, conventional X-ray powder diffraction was performed with a Panalytical diffractometer, model X’Pert Pro MPD (Cu Kα radiation, 40 kV, 40 mA).

3. Results and discussion

3.1. XRD/XRF portable system

3.1.1. Red and yellow pigments

The XRD/XRF portable system revealed that two types of red pigments, vermilion and red ochre, were present in the Romanwallpaintings. In the Arabicpaintings, only haematite was detected (Table 1).

Vermilion (HgS) was easily identified via XRF; mercury and sulphur were detected in Roman samples 5 and 11 (Fig. 2a). Fig. 3a shows the XRD patterns recorded by the 2-dimensional detector and, after conversion, the conventional 1-dimensional diagram of sample 11 (Fig. 3b) (The XRD diagram of sample 5 is very similar to that of sample 11). In Fig. 3a, each ring corresponds to diffracting crystallographic planes (incident beam at an angle θ from the planes) for a set of grains under a suitable orientation. The continuous rings that appear in Fig. 3a were formed by the superposition of reflections of cinnabar and calcite grains, and the intensity profile along the diffraction rings is expressed by the changes of colouration observed. As shown in Fig. 3a, the cinnabar rings have different colour (yellow-green) than those of calcite (pink), showing the former higher intensity values. Thus, the results indicated that the particle size of cinnabar was larger than that of calcite. Intensity values are also function of other factors such as the proportion of phases in the sample; in this case, there should be (in mass) more cinnabar than calcite in the paint. Also we should take into account the high reflecting power and structure factor of the cinnabar, which provide values to be added to those derived from particle sizes and phase proportion. Mercury sulphide has been used by artists since antiquity (Gettens and Stout, 1966). Natural (from mining sources, also called cinnabar) and synthetic vermilion have been used as pigments; however, XRD and XRF cannot distinguish between natural and synthetic variants (Van der Snickt et al., 2008). Vermilion was known to the Romans as minium and was one of their most valuable pigments (Pliny the Elder, 1985). As Theophrastus asserted 200 years before Vitruvius, the cinnabar

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mines used by the Romans were of Spanish origin and were located in Sisapo (Almaden at the present time) ( [Mazzocchin et al., 2008] and [Duran et al., 2010b]).

The identification of haematite (α-Fe2O3), red ochre (haematite, silica, clays) and yellow ochre (goethite α-FeOOH, silica, clays) could not be achieved by XRF alone because iron is present in everywhere. In the present study, relative high concentrations of iron were detected by XRF in samples 1 (Arabic), 3 and 7 (both Romans) (Fig. 2b). The red pigment haematite was detected by XRD in samples 1 and 3 (Fig. 4). Alternatively, goethite, a yellow pigment, was detected in samples 3 and 7 (Fig. 4 and Fig. 5). Calcite (CaCO3) and quartz (SiO2) were also observed in all of the samples. Moreover, the characteristic fingerprint peak of clays at 2θ ≈ 20° (Brindley and Brown, 1980) was observed in Roman samples 3 and 7; however, peaks attributed to clays were not observed in Arabic sample 1. These results suggest that two different types of pigments were used, depending on the period in which the paintings were made. In particular, red ochre and yellow ochre were observed in Romanpaintings, and haematite was detected in Arabicpaintings. The ratio of calcite (2θ = 29.5°)/quartz (2θ = 27.6°) XRD peaks was higher in the superficial layers of the Arabic fragments than in the Roman samples (Figs. 4a, c and 5a). Continuous smooth diffraction rings corresponding to small haematite and goethite particles sizes were collected in the imaging plates (Figs. 4b, d and 5b). Typically, natural iron oxyhydroxides and iron oxides were mixed with clay minerals (kaolinites, illites, smectites, etc) and used as pigments (Hradil et al., 2003). Red ochre was one of the first pigments used in ancient paintings ( [Menu, 2009] and [Pallecchi et al., 2009]), and Roman artists ( [Mazzocchin et al., 2004], [Weber et al., 2009] and [Aliatis et al., 2010]) used both natural and artificial ochres, which were obtained by the calcination of yellow ochres (Pliny the Elder, 1985). Hispano-arabicpainting is often dichromatic, and the design is made in red on the white mortar. The symbolic aspects of red colours in the Middle Ages are well-documented; however, in the studied artwork, we believe that haematite was used as a pigment due to its ease of preparation, location and cost. Moreover, the colour of haematite provides a stark contrast against a white background and promotes a strong visual effect (Rallo Gruss, 2003).

3.1.2. Green pigments

Celadonite (K(Mg, Fe, Al)2(Si, Al)4O10(OH)2) was detected by XRD and attributed to the green coloured pigment in Roman sample 12 (Fig. 6). The quartz grains and celadonite particles in sample 12 were large and relatively intense rings were observed. In addition, the diffraction rings were dotted, indicating a non-homogeneous distribution or isolated particles (Fig. 6b) ( [Rodriguez-Navarro, 2006] and [Rodriguez-Navarro et al., 2006]). One of the mean XRD peaks of mica compounds is observed at 2θ = 9°. However, in experiments performed in reflection mode, low angles (2θ < 16–17°) are lost due to the experimental restrictions of the portable XRD/XRF system. Thus, to confirm the presence of celadonite, conventional X-ray powder diffraction experiments were performed on sample 12, and diffraction peaks corresponding to the aforementioned phase (2θ ≈ 8.8°, 24.5°, 33.3° and 34.8°) were observed; these results are similar to those obtained by using the XRD portable system. “Green earths” used as pigments since antiquity are still in use in the creation of artwork: they are mainly constituted of micas celadonite and/or glauconite (phyllosilicates), both minerals are formed under different geological conditions (Ospitali et al., 2008). In these paintings, only celadonite has been detected. Both minerals are iron-rich dioctahedral micas that are deficient in potassium and have small tetrahedral substitution (Brindley and Brown, 1980). Celadonites and also glauconites have been studied by numerous methods (Drits et al., 1997) and are typically

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present as dull grey–green to bluish green masses. In the present study, iron and potassium were detected by XRF, along with copper (Fig. 2c), which was not justified with the detection of any compound by XRD. A copper source is not typically used for micro-XRF portable systems because copper fluorescence lines are always present in the spectra; thus, the detection of copper is often difficult ( [Gianoncelli et al., 2008] and [Duran et al., 2009]). However, in the XRF spectrum of sample 12, a Cu Kβ peak was clearly visible (Fig. 2c magnification), indicating that the Cu was present in the sample (Duran et al., 2011).

3.1.3. White and black pigments

The detection of calcite by XRD as the main component was certain in all the surfaces of the fragments studied (Table 1). In the fresco wallpainting technique, pigments are mixed with water to make a suspension (paint) and applied to the wet plaster, which is made of hydrated lime and aggregates. Dissolved lime diffuses from the plaster into the paint layer and then carbonates, forming calcite and acting as a binder for the pigment. As shown in Fig. 2, significant amounts of calcium were also detected in the XRF spectra. Furthermore, in samples 1 (Arabic), and 3, 5, 7, 11 and 12 (Roman), calcite was detected by XRD (Fig. 3, Fig. 4, Fig. 5 and Fig. 6) together with coloured compounds (cinnabar, haematite, goethite and celadonite) and quartz. Alternatively, in white-coloured fragments, only calcite and quartz were detected, as shown in the XRD spectra of Arabic sample 2 and Roman fragments 4 and 13.

In sample 14 (the black Roman fragment), only calcite and quartz were detected by XRD. No characteristic chemical elements responsible for the black colour were observed by XRF. Light elements such as carbon or phosphorus, which are normally responsible for the black colour, are not usually detected by XRD/XRF due to the strong absorption of X-rays due to the air (2.5 cm) between the sample and the XRF detector. For instance, at the energy of Si–K (1.74 keV), X-ray transmission in 1 and 3 cm of air is approximately 40% and 5%, respectively ( [Gianoncelli et al., 2008] and [De Viguerie et al., 2009]). Thus, other techniques were used to characterise black pigments.

3.2. Optical and scanning electron microscopy and EDX analyses

To conduct EDX and SEM analyses, samples of the wallpainting fragments were collected and cross-sections of the material were done in some cases. The information provided by these techniques allowed us to study the paintings in more detail. In particular, the distribution of the layers was evaluated, and the minority components and the morphology of the particles were analysed.

3.2.1. Red and yellow pigments

The EDX spectra of the red layer of the Arabic sample 1 indicated that the material consisted primarily of Fe, Ca, Si and Al. However, in punctual analyses, the presence of almost only iron (Fig. 7a) was detected, likely due to the presence of haematite, as previously observed by XRD. The cross-section of the Roman sample 3 showed the presence of two differentiated colour layers by optical microscopy (Fig. 8a): an external red and an internal yellow one, with similar elemental composition: Si, Ca, Fe, Al, Mg and K (by EDX analyses).

The EDX analyses of the red and yellow layers of the cross-sections of Roman (samples 3 –red and yellow– and 7 –yellow) and Arabic (sample 1 –red) fragments (Fig. 7b and c) were

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compared. The ratios silicon/calcium and aluminium/calcium peak intensities are higher for Roman samples than for the Arabic one. The ratio silicon/iron is lower for the Arabic sample, showing that higher amounts of silicon and aluminium appeared in the Roman fragments and of iron in the Arabic one. In addition, punctual analyses and elemental mappings of the Roman samples seemed to indicate that the presence of iron was associated with aluminium and potassium (forming clays), as shown in Fig. 9a. Iron was also observed in the Arabic sample (Fig. 9b); however, iron in the Arabic fragment was associated with calcium and was not correlated with aluminium and potassium. In fact, silicon appeared in the zones in which iron was absent. These results suggest that Arabs employed haematite as a pigment and Romans used red ochre and yellow ochre for colouration. Although the XRD results support this assertion (Fig. 4 and Fig. 5), it is unclear whether the clay content of the ochre pigments was naturally high, or if clay and sand were combined with the pigment and hydrated lime in the mortar-forming process, as suggested by other authors (Weber et al., 2009).

The morphology of the particles was studied by directly visualising the fragments via SEM or by collecting powders from the surface of the fragments. As shown in Fig. 10a, calcite particles (approximately 1–3 μm) and granular haematite particles with a size less than 0.5 μm were observed in the Arabic sample. Alternatively, in the Roman sample, granular goethite particles with a diameter less than 0.5 μm were detected. As shown in Fig. 10b, the goethite present in the Roman samples was associated with relatively large, laminar particles of clays. Moreover, in Roman samples, characteristic laminar clay particles (size around 10 μm) were observed in red and yellow pigments (Fig. 10c). The morphology results obtained in the present study are similar to those commonly described in the literature ( [Gettens and Stout, 1966] and [Henning and Störr, 1986]) and are in agreement with the qualitative results derived from the XRD 2-dimensional images.

Using SEM-EDX, two different compositions were observed in the upper zone of the cross-section of Roman sample 11 (Fig. 8b). Moreover, Hg and Fe mappings indicated that two different red layers were present in the material. In particular, the upper layer corresponded to an Hg-based compound, and the inner layer was attributed to a Fe-based mineral (Fig. 9c). According to the XRD results, only cinnabar, calcite and quartz were present in the fragments (Fig. 3). Thus, the penetrability of X-rays played an important role in the analysis of sample 11. The X-rays attenuation length is defined as the depth into the material measured along the surface normal where the intensity falls to 1/e of its value at the surface (Henke et al., 1993). To calculate X-ray penetration, the composition and density of the material (cinnabar), the photon energy (Cu Kα radiation) and the incidence angle (around 10°) were considered. The theoretical attenuation length of cinnabar was 1.105 μm, and cinnabar grains with a diameter of approximately 2–6 μm were observed by SEM. Thus, due to the fairly homogeneous distribution of large cinnabar grains (previously observed in the 2-dimensional XRD images shown in Fig. 3) in the surface layer, X-rays from the XRD/XRF portable system could not penetrate into the inner layers. As a result, iron-based compounds (possibly red ochre) were not detected. Coarse cinnabar grains with various sizes were observed in the images (Fig. 10d). The grains appear to be broken fragments rather than single rounded homogeneous crystals; thus, the cinnabar used in the pigment is likely a natural variety.

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3.2.2. Green pigments

The EDX spectra of sample 12 revealed that Si, Ca, Fe, and also K, Al and Mg were present in the green-coloured fragment (Fig. 7d). The association of the colour with this kind of composition leads us to the conclusion that the colour can be attributed to green earth, also according to the presence of quartz and celadonite (detected by XRD) (Fig. 6). Microscopically, platy crystals, characteristics of celadonite, were observed (Fig. 10e). In addition to green earth, another compound based on calcium, copper and silicon was detected in some punctual EDX analyses; similar results were previously observed by the XRF analyses (Fig. 2c magnification). Hexagonal crystals of about 20 μm were likely applied, possibly to retain the colour (Fig. 10f). These results seemed to indicate the presence of Egyptian blue, a pigment which is very often added to green earth pigments in Romanwallpaintings.

3.2.3. Black and white pigments

Phosphorus and calcium were detected in sample 14 by SEM-EDX (punctual analyses) (Fig. 7e), which was associated to the presence of ivory black. In addition, carbon-based black pigments were suspected by micro-Raman spectroscopy due to the appearance of broad Raman bands centred near 1330 and 1590 cm−1 (Figure not shown) (Duran et al., 2011). Based on these results, we concluded that two types of pigments were very possibly responsible for black coloured fragments (phosphor and carbon-based compounds).

High amounts of calcium were detected in white fragments and in white areas of other fragments. Fig. 10g and h shows the morphology of calcite and quartz in the superficial zones of the mortars. Granular calcite displayed particle sizes of 1–3 μm, and continuous rings with low intensities were observed in the XRD 2-dimensional images, indicating that a large number of small calcite grains were homogeneously distributed throughout the superficial layer of the samples.

4. Conclusions

During the archaeological excavations in the PatiodeBanderas of RealesAlcazares’ Palace, fragments of Roman and Arabicwallpaintings were discovered. Red, yellow, white, green and black coloured fragments were collected from the Romanwallpaintings, and red and white-coloured fragments were obtained from the Arabicpaintings (Table 1).

To produce the red colour, different pigments were used, depending on the origin of the painting. Namely, in the Romanpaintings, red ochre and vermilion were employed. Alternatively, in the Arabicpaintings, haematite was used. The distinction between red ochre and haematite was possible thanks to the use of XRD and SEM-EDX. For instance, haematite and clays (forming red ochre) were detected by XRD in some of the red samples of Roman origin. Punctual chemical analyses and elemental mappings revealed that iron was associated with aluminium and potassium in these samples. Similar to red paints, Roman artists used yellow ochre to obtain yellow decorations. Alternatively, haematite was detected in the Arabicpaintings; in particular, the results indicated that iron and calcium were associated. It is known the admiration, emulation, assimilation and continuity of Islamic art from the ancient Roman world. Hispano-arabic art is a fusion of visigothic and Roman Iberian art and has a strong base in local tradition ( [Maravall, 1992] and [Rallo Gruss, 2003]).

The XRD results indicated that quartz and celadonite were present in the green coloured fragments, and the EDX results showed the presence of Si, Ca, Fe, K, Al and Mg; thus, we

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concluded that the green colour of Roman samples was achieved with green earth. Moreover, Egyptian blue was also detected by SEM-EDX and XRF. The composition of the black fragment was based on phosphor (ivory black) and carbon-based pigments.

The pigments detected in the Romanwallpaintings studied in this paper are seen to be those that are quite normally encountered in Roman villas; namely, red and yellow ochres, vermilion, green earth, Egyptian blue and carbon and phosphor-based black pigments (carbon black and ivory black) were detected ( [Edreira et al., 2001], [Mazzocchin et al., 2004], [Edwards et al., 2009], [Weber et al., 2009], [Aliatis et al., 2010] and [Duran et al., 2010b]).

In addition, a first qualitative approach about the size and shape of the particles in the pigments was determined by acquiring XRD images with a 2-dimensional detector (imaging plate) and tested by scanning electron microscopy. The results obtained from both techniques were in agreement. In particular, the results revealed that haematite and goethite displayed small particle sizes (<0.5 μm), and celadonite and calcite possessed similar particle sizes (1–3 μm). Moreover, celadonite and calcite particles were smaller than those of cinnabar (2–6 μm) and other laminar clays detected in ochre (10 μm). In addition, Egyptian blue particles were approximately 20 μm in diameter. The data obtained in the present study coincide with those described in the literature.

From a technical point of view, the portable XRD/XRF system developed by the C2RMF laboratory was used to successfully characterise the paintings. With this equipment, elemental, chemical and structural analyses were combined, and non-destructive analyses were achieved. In addition, the micro-structures of the samples and the grain size of the particles were determined. It is important to point the high quality of the results obtained from the new portable XRD/XRF system. However, SEM-EDX allowed a more thorough identification of the components of pigments. As a result, the sequence of the layers and the morphology of the particles were described in detail.

Acknowledgements

This work was supported by project BIA 2009-12618, EU-ARTECH (contract number RII3-CT-2004-506171), MEC/FULLBRIGHT 2007 and JAE Doc 088. The authors gratefully acknowledge C2RMF staff (especially Dr. Jacques Castaing), Miguel Angel Tabales from the RealesAlcazares of Seville, Cristina Gallardo from the Materials Science Institute of Seville, Almudena Muñoz (architect) for their assistance and the useful comments from the reviewers. Samples were provided by Miguel Angel Tabales.

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Table 1. Description of the samples collected from the wallpaintings: period, notation (sample number), micrograph, fragment dimensions, composition and analytical techniques employed for characterization.

Period Sample number

Photograph of the fragment

Fragment dimensions Composition Techniques

employed

Roman (1st century BC)

3 3.5 × 1.5 × 1.5 cm

Red ochre, yellow ochre. calcite, quartz

XRD-XRF portable, O.M., SEM-EDX

4 6.5 × 4.0 × 1.5 cm Calcite, quartz

XRD-XRF portable, O.M.

5 2.5 × 2.5 × 1.5 cm Vermilion, calcite

XRD-XRF portable, O.M.

7 1.0 × 0.8 × 1.0 cmYellow ochre, calcite, quartz

XRD-XRF portable, O.M., SEM-EDX

11 2.3 × 1.5 × 0.8 cm

Vermilion, red ochre, calcite, quartz

XRD-XRF portable, O.M., SEM-EDX

12 5.5 × 3.0 × 1.5 cm

Green earth, Egyptian blue, calcite, quartz

XRD-XRF portable, O.M., SEM-EDX

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Period Sample number

Photograph of the fragment

Fragment dimensions Composition Techniques

employed

13 1.5 × 1.5 × 0.9 cm Calcite, quartz

XRD-XRF portable

14 8.5 × 6.0 × 1.7 cm

Carbon based black, ivory black, calcite, quartz

XRD-XRF portable, micro-Raman, O.M., SEM-EDX

Arabic (11th century AD)

1 4.5 × 4.5 × 1.5 cmHaematite, calcite, quartz

XRD-XRF portable, O.M., SEM-EDX

2 1.3 × 1.0 × 1.0 cm Calcite, quartz

XRD-XRF portable, O.M.

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Figure captions

Figure 1. (a) Plan of the archaeological site of the PatiodeBanderas of RealesAlcazares’ Palace, including the different remains of construction from the 2nd century BC to the 11–13th century AD (b) and (c) show the plans of the PatiodeBanderas and the location of Roman building rests (from 1st century BC) and Arabic buildings and streets (from 11th to 13th century AD) from which Roman and Arabicwallpaintings were discovered (sampling zones are marked with green and blue squares) (plans were provided by M.A. Tabales). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Figure 2. XRF spectra collected from the superficial layers of the wallpaintings fragments: (a) Roman red sample 5; (b) Arabic red sample 1; (c) Roman green sample 12 (and magnification). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Figure 3. (a) XRD pattern of the Roman sample 11 as recorded in reflection mode on the 2-dimensional detector (coloured surface in fragment); (b) Conventional XRD diagram (Roman sample 11) [Cin = cinnabar; C = calcite; Q = quartz]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Figure 4. XRD diagrams and XRD patterns obtained from the 2-dimensional detector: (a,b) Arabic sample 1 (coloured surface in fragment) (black diagram), and (c,d) Roman sample 3 (coloured surface in fragment) (red diagram) [H = haematite; G = goethite; C = calcite; Q = quartz; Cl = clays]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Figure 5. XRD diagram (a) and XRD pattern (b) of Roman sample 7 (coloured surface in fragment) [G = goethite; C = calcite; Q = quartz; Cl = clays]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Figure 6. Conventional XRD diagram (a) and XRD patterns (b) of Roman sample 12 (coloured surface in fragment) [Cd = celadonite; Q = quartz; C = calcite; Cl = clays]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Figure 7. EDX spectra corresponding to: (a) the punctual analysis on the red layer of the cross-section of Arabic fragment 1; (b) the general analysis on the red layer of the cross-section of Roman fragment 3; (c) the general analysis on the red layer of the cross-section of Arabic fragment 1; (d) the general analysis on the green layer of the cross-section of Roman fragment 12; (e) the punctual analysis on the cross-section of Roman fragment 14. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Figure 8. Cross-sections micrographs of: (a) Roman sample 3 (red and yellow), (b) Roman sample 11 (two red layers). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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Figure 9. Elemental mappings performed on: - (a) the yellow and red layers of the cross section of sample 3 (Roman): (a-1) secondary electron images, (a-2) Fe mapping, (a-3) Al mapping, (a-4) K mapping; - (b) the red layer of the cross section of sample 1 (Arabic): (b-1) secondary electron images, (b-2) Fe mapping, (b-3) Ca mapping, (b-4) Si mapping; - (c) the red layers of the cross section of sample 11 (Roman): (c-1) secondary electron images, (c-2) Fe mapping, (c-3) Hg mapping. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Figure 10. SEM images showing the morphology of: (a) haematite particles and calcite grains in Arabic sample 1; (b) goethite and clays particles in Roman sample 3; (c) clays associated with haematite and goethite particles in Roman sample 3; (d) cinnabar grains in the cross-section of Roman sample 11; (e) green earth (mainly celadonite) in Roman sample 12; (f) Egyptian blue grains in sample 12; (g) calcite grains (Arabic sample 1); (h) quartz grains (Roman sample 3).

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Figure 1

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Figure 2

23

Figure 3

24

Figure 4

25

Figure 5

26

Figure 6

27

Figure 7

28

Figure 8

29

Figure 9

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Figure 10

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