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Green pigments of Roman mural paintings from Seville Alcazar
CLAY-03373; No of Pages 9 Applied Clay Science xxx (2015) xxx–xxx
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Research paper
Green pigments of Roman mural paintings from Seville Alcazar Jose Luis Perez-Rodriguez ⁎, Maria del Carmen Jimenez de Haro, Belinda Siguenza, José María Martinez-Blanes Materials Science Institute of Seville (CSIC-Seville University), Americo Vespucio 49, 41092 Seville, Spain
a r t i c l e
i n f o
Article history: Received 6 January 2015 Received in revised form 14 March 2015 Accepted 17 March 2015 Available online xxxx Keywords: Roman wall painting Celadonite Glauconite Egyptian blue Egyptian green Support
a b s t r a c t We report here a study of 30 fragments of green wall paintings from Roman times found in the Patio de Banderas excavation in Seville Alcazar. The sample characterisation was realised using optical microscopy, colourimetry, infrared and micro-Raman spectroscopy, X-ray diffraction, and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. The study of these pigments is important because it can help determine the source or the pictorial technique used. The samples studied in this work have been divided into two groups, according to the composition of their green pigments. In the first group, celadonite has been characterised as the primary component of the green colour; chlorite was also detected. Particles constituted by chromium accompanied by aluminium, iron and zinc were found in all studied samples of this group. Chlorite and chromium oxide could also be responsible for the green colour. The presence of chromium suggested the presence of green colour pigment from Verona. In the second group, a mixture of celadonite and glauconite was detected and could be responsible for the green colour observed. The addition of refracting material such as Egyptian blue was also used. A mixture of Egyptian green and Egyptian blue together with celadonite and glauconite was also found. Four classes of intonaco were recognised and classified based upon the composition of the aggregates. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The archaeological excavation of the Patio de Banderas was performed by Tabales (2010, 2012), and was organised by the Foundation of the Reales Alcazares of Seville to obtain information about the stratigraphy of the first enclosure of the Real Alcazar. The Patio de Banderas excavations found remains belonging to the Early Iron Age and structures belonging to ancient Roman buildings, the most important of which was the one raised by the opus africanum technique. A large building from the end of the fifth century built around a columned courtyard was also found; this building perhaps belonged to religious units linked to a church outside the walls. The most important of the excavated Roman buildings belonged to the beginnings of Roman urbanism during the republican phase I (circa 100 BC), the republican phase 2 (60–30 BC) and reforms of the imperial period (1st and 2nd centuries AD). Coatings in situ have not survived but many polychrome fragments in the imperial levels have, dating to the late republican time and for the first imperial time, richly decorated interiors with quality plastering. Paintings and colour remains from Roman Ages have been discovered and studied for over a century. Roman artists had a wide knowledge of green pigment, including verdigris, malachite and green earth (Singer et al., 1954; Eastaugh et al., 2004). Important discoveries were performed in Pompei and Rome (Mazzocchin et al., 2003; Aliatis et al., 2009; Duran et al., 2011; Piovesan et al., 2011). In Spain, scientific
⁎ Corresponding author. Tel.: +34 954489532. E-mail address: [email protected] (J.L. Perez-Rodriguez).
research in archaeological finds has been developing (DomenechCarbo et al., 1996; Edrein et al., 2001; Duran et al., 2010). Other Roman wall paintings from other countries have also been studied (Maggiolaro et al., 1997; Gliozzo et al., 2012). Malachite ores came from Armenia, Cyprus, Macedonia and Spain. The one from Armenia was the most precious pigment (Augusti, 1967; Pliny, 1968; Vitruvius, 1999; Aliatis et al., 2009). Pliny (1968) mentioned that malachite was a rare and expensive material that was also called chrysocolla, which is the name now used for hydrated copper silicate. Green earth (i.e., creta viridis or appianium in ancient times) was typically used in wall paintings since ancient times and is still used (Grissom, 1986; Grygar et al., 2003; Hradil et al., 2003). The minerals responsible for the colour of green earth are types of clay micas, glauconite ((K0.8Na0.01Ca0.04)(Fe3+1.31Al0.28Mg0.4)(Si3.58Al042)4O10(OH)2 and celadonite ((K0.94)(Fe3 +0.72Al0.42Mg0.6Fe2 +0.24(Si3.9Al0.1)4O10(OH)2 (Rieder et al., 1998). Also smectite, chlorite, serpentines and pyroxenes can be responsible of this colour (Grissom, 1986; Hradil et al., 2003, 2004; Usman et al., 2012; Valanciene et al., 2014). Glauconite and celadonite have similar compositions but are formed under different geological conditions: celadonite is found in amigdules or fractures in metamorphic rocks, while glauconite is found in the form of small greenish pellets (i.e., green sand) in shallow marine sedimentary rock (Ospitali et al., 2008). Both minerals consist of a layer of octahedral coordinated cations (Al, Fe3+, Fe2+ and Mg), sandwiched between two sheets of silicium tetrahedral and have small tetrahedral substitutions; an interlayer of K ions holds the layers together (Brindley and Brown, 1980). Celadonites and glauconites have been studied by numerous methods (Drits et al., 1997) and are typically found as dull grey-green
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Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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to bluish green masses. Mineralogical analyses in the field of cultural heritage are rare and often limited to the identification of the generic class “green earth” without specific characterisation of the mineralogical species present in the artefacts. The most famous deposits of green earth can be found near Verona, Italy, as well as in Tyrol, Bohemia, Saxony, Poland, Hungary, France, Cyprus and England. Verona earth is constituted by celadonite found in basaltic rocks. However, the presence of glauconite cannot be excluded from a green pigment because it can be found in sand stone levels as a result of mixing between extrusive tertiary products with eocenic sediments (Aliatis et al., 2009). The similarity in the structure and composition of glauconite and celadonite makes its analytical distinction difficult. In this study, we were not able to positively distinguish glauconite from celadonite; however, different experimental techniques have been used to distinguish both minerals used in Roman wall paintings; these techniques include Móssbauer (Castellato et al., 2000), Raman and EDS (Moretto et al., 2011), XRD (Rafalska-Lasocha et al., 2010), FT-IR, EDS, AAS spectrophotometric analysis, EPR, and micro-Raman spectroscopy (Genestar and Pons, 2005; Ospitali et al., 2008; Clementi et al., 2011; Moretto et al., 2011). In a recent work, Duran et al. (2011) detected glauconite but not celadonite in some wall painting samples of different colours from Pompei and Herculaneum by synchrotron radiation-high-resolution powder diffraction (SH-HRPD). A common practice of Roman wall painters was the addition of Egyptian blue to green earth to produce more brilliant colours (Mazzocchin et al., 2003). Egyptian craftsmen created a blue pigment (i.e., Egyptian blue) by firing a mixture of compounds containing silicon, calcium and copper with a soda or plant-derived potash as a flux at 850–1000 °C. This technology was lost after the seventh century (Pages-Camagna and Colinart, 2003). The characterisation of this pigment in ancient times has been widely studied (Mazzocchin et al., 2003; Eastaugh et al., 2004; Pages-Camagna et al., 2010; Clementi et al., 2011; Duran et al., 2011; Piovesan et al., 2011). The green colour could also be obtained from the mixture of Egyptian blue with a yellow pigment or this mixture could be added to other green pigment, such as malachite or green earth, to obtain a darker colour (Clementi et al., 2011). A pigment with the same chemical elements as Egyptian blue called Egyptian green with a turquoise colour was also used. This pigment is also called green frit (Ulrich, 1987; Schiegl et al., 1992). It has been considered to be a misfired Egyptian blue (Jaksch et al., 1983; Ulrich, 1987); the colour has also been interpreted to indicate the presence of iron coming from the sand (Kaczmarczyk and Hedges, 1983) or a weathered Egyptian blue. The alteration of this pigment generates only copper carbonate or copper chloride. However, the Egyptian blue and Egyptian greens are two entirely different pigments produced following different recipes (Bianchetti et al., 2000; Pages-Camagna and Colinart, 2003; Schiegl and El Goresy, 2006). The Egyptian green pigment is produced from the same components of the Egyptian blue simply changing the concentration and temperature conditions to obtain a glassy phase where Cu2+ occupied an octahedral coordination and consequently a green colour (Eastaugh et al., 2004). The colour tone of the Egyptian green pigment should depend on the origin of copper impurities in the sand and manufacturing temperature (Canti and Heathcote, 2002). The goal of the present work was the study of the green colour of several fragments from the Patio de Banderas excavation. The identification and study of these pigments used in Roman wall paintings found in this excavation will obtain information on the technique used by Roman. This study can provide to the archaeologists and art historians precise information on the technique used in the creation of the work itself. In addition, the results can provide conservators and restorers with guidelines on the materials necessary for conservation. This work was focused on the characterisation of glauconite and celadonite and the techniques on these wall paintings, which included non-invasive methodologies integrated by focused micro-invasive analysis. This work was also focused on the characterisation of Egyptian blue
and green mixture with celadonite and/or glauconite. This identification could help trace possible routes of Roman painting in Spain. 2. Experimental 2.1. Materials 30 green coloured fragments from the Patio de Banderas supplied by Professors Tabales and Duran of Seville University were analysed. The interest for the study has been described by Tabales, 2012. Fig. 1 shows several fragments of the samples studied in this work. The fragments were buried; the samples were in excellent conditions and were not subjected to any previous restoration processes. The size of the samples was variable (dimensions of 12 cm × 7 cm to 3.5 cm × 1.5 cm.) The thickness of the fragments ranged from 3 cm to 0.9 cm including the mortar and pictorial layer. The cross sections were prepared from small samples taken from the wall painting fragments following the previously described methodology (Khandekar, 2003). 2.2. Techniques 2.2.1. Colourimetric analysis Colour measurements were performed on the samples with a Dr. Lange Micro Color Labor station. Experimental data were recorded according to the CIE (Commission International De L' Éclairage); lightness L*, red-green coordination a* and yellow-blue coordinate b*. 2.2.2. Optical microscopy The cross-sections were prepared starting from a mould of methyl polymethacrylate where the samples were placed horizontally and refilled up with epoxy resin of methylmethacrylate. The resulting material was cut with a fretsaw equipped with a Bahco 302-835-blade, which was polished with an automatic polishing machine and various grades of sand paper and was finished with a cloth. The cross sections were observed and photographed using a Nikon OPTIPHOT (× 25, × 50 and ×100) optical microscope. Fig. 2 shows a selection of the cross sections prepared from the extracted samples. The thickness of the colour layers ranged from 3 μm to 25 μm. 2.2.3. Micro-Raman laboratory equipment The integrated dispersive Horiba Jobin Yvon LabRaman system was used to record the Raman spectra. These experiments were performed directly on the artwork or on the cross sections. Two external visible diode lasers with a solid-state source are available in this apparatus: 532.14 nm (green) and 784.56 nm (red). However, we primarily used the 784 nm source to minimise fluorescence from the organic medium or from the pigments/dyes themselves. The instrument has a chargecoupled device (CCD) detector and a grating of 600 grooves/mm. A confocal optical microscope is coupled to the Raman spectrometer. The majority of the measurements presented in this paper were collected at 100× magnification. The size of the analysed zones depends on the microscope magnification. At 100 ×, the spot sizes were 0.72 μm and 1.06 μm for the green and red lasers, respectively, and the spatial resolution was 0.53 μm. Each Raman spectrum was recorded for 8–12 min with a spectral resolution of 2 cm− 1. The standard spectrum was obtained from the Jobin Yvon Commercial Databases: www.horiba. com/scientific/products/raman-spectroscopy/accesories/raman-spectrallibraries (ancient pigments). 2.2.4. Fourier transform infrared spectroscopy (FTIR) The Fourier transform infrared study was performed using a Jasco FTIR 6200. Small samples were ground, and a disk with KBr was prepared.
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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Fig. 1. Several fragments of the samples studied in this work.
Fig. 2. Selection of the cross sections prepared from the extracted samples. Group i) a–d. Group ii) e–h. Painting supports i–l.
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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2.2.5. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM–EDX) Elemental chemical analyses of the cross sections were obtained using a HITACHI S-4800 SEM instrument equipped with a Bruker XFlash Detector 4010 EDX analyser at an accelerating voltage of 20 kV. The EDX quantitative microanalyses were obtained using the ZAF method of correction.
According to the mineralogical composition obtained in this work, the green pigments characterised have been divided into two groups: i): green colour was only observed in this group, representative crosssections are shown in Fig. 2a, b, c and d, and ii) mixture of blue and green colours was observed in this group, representative crosssections are shown in Fig. 2e, f, g and h. The fragments of both groups were found in different zones of the excavation.
2.2.6. X-ray diffraction (XRD) Grazing incidence XRD was used to study the surface of the fragments. The irradiated surface was 20 mm × 1.5 mm. X-ray powder diffraction was performed on a PANalytical X'PERT Pro MPD diffractometer with lambda = 1.540509 Å at 45 kV and 40 mA. A Pixcel solid-state detector was used. The study was performed directly on the fragments using XRD. Conventional XRD was also performed with the same equipment on ground small samples.
3.1. Group i)
2.2.7. Portable X-ray fluorescence (XRF) In-situ measurements were also performed using a portable XRF system (Gianoncelli et al., 2008). An X-ray tube (40 kV, 700 μA) with a copper anode was used. The XRF detector was a silicon drift detector (Röntec GmBH) and had an active area of 5 mm2 and a full width at half-maximum (FWHM) of 150 eV at 5.9 keV. It was Peltier-cooled to −10 °C and was located at 90° to the X-ray tube and on the axis normal to the analysed sample surface. At the exit of the tube, we used a slit of 0.5 mm; therefore, the measured area was approximately 9 mm2. The chemical analysis performed by portable XRF yields information of the external composition of the sample. For XRF, the depth of analysis depends on the nature of the chemical elements and the energy of the X-rays used for the detection of the elements. 3. Results and discussion Colorimetric analysis of the green colour surface of the fragments studied was accomplished by considering the L⁎ a⁎ b⁎ colour space. The lightness L⁎ values and saturation C are not given because they depended on the paint techniques and on the influence of the white colour used as a binder and support material. The relationship between a⁎ and b⁎ is shown in Fig. 3. A high heterogeneity of chromatic values was found in each area of green colour. The heterogeneity of the green colours was most likely due to the different colours near or under them. In some fragments, 4 green colours with different hues in the same colour area were found to be made with the same pigment but with different percentages of the pigment and binder. In other samples, mixtures between different green and blue pigments were detected. This technique was not able to differentiate between celadonite and glauconite, as described by Moretto et al. (2011).
Fig. 3. Representation of a⁎ (red-green coordination) versus b⁎ (yellow-blue coordinate) parameters of colourimetric analysis.
The chemical analysis performed by portable XRF is shown in Table 1. Ca(+), Cr, Fe, K, Ni, Ti, and Sr have been detected in these samples. These data suggested the presence of green earth. The most important information obtained was the presence of chromium that will help elucidating the source of this pigment. Despite its portability and facility in analysis and handling data, XRF is not the most powerful technique for obtaining information of all layers of a cross-section due to its thickness; thus, XRF was not adequate to distinguish the distribution of different layer analysed. In this work, the SEM–EDX performed on the cross-sections (i.e. Fig. 2a–d) helped complete the characterisation of different particles and distribution of the different layers. In Table 1, chemical analyses of green grains are shown. The chemical analysis of some grains showed the presence of chromium. The punctual chemical analysis of other green grains showed the presence of Si, Al, Mg, Fe, K and Ca (Fig. 4a), which suggested the presence of celadonite and/or glauconite. Due to the high resolution of SEM–EDX, it is possible to differentiate between different components present, including glauconite and celadonite. Based on the ratio Si:Al:Mg, it is possible to differentiate glauconite from celadonite: when Si N Al N Mg, glauconite is present; however, in celadonite, Si N Mg N Al. The quantitative chemical analyses performed by punctual chemical analysis and the atoms % Fe/Mg and K/ (Si/Al) of green particles is shown in Table 2. The compositions are similar to the stoichiometric composition of celadonite. The representation of Fe/Mg versus K/(Si/Al) showed that it is possible to include this samples in the celadonite field from Verona based on the study performed by Hradil et al. (2011). In all samples, particles of Cr (see Fig. 4b–d, f) were detected. In addition, this chemical element was accompanied by Fe (Fig. 4b), Al (Fig. 4c), Ti (Fig. 4d) and Si (Fig. 4f); Zn and Ca were also detected. Particles constituted primarily by Si were also found (Fig. 4e). It is known from the literature that terra verte may contain chromium oxide and cobalt–aluminium, which make a pigment green (Hradil et al., 2004). However, chromium is only present in green earth from Verona. These results confirm that the green earth is constituted by celadonite and that the pigment originated from Verona. The presence of particles made primarily of Cr suggests that this element is not included in the structure of mica (i.e., celadonite) and appeared as chromium oxide with the mica. Chromium oxides are also green in colour, which may imply that they are responsible for the colour of this pigment. The XRD analyses performed on the surface of the fragments (Fig. 5) indicated the presence of mica (Fig. 5b) (i.e., celadonite and/or glauconite). In some of these samples, reflections at 14.00, 7.05, 3.74 Å, etc. (Fig. 5a) also appeared and may be attributed to the presence of chlorite, which is also green in colour. The XRD diagrams obtained in these samples after acid treatment confirmed the presence of chlorite. In a fragment with a dark and light green colour the only differences found were the percentages of the green pigments (i.e., mica and chlorite) (see Fig. 5c and d). Iron oxides were also characterised (Fig. 5a, b). The XRD performed by grazing angle incidence do not allow a clear differentiation of celadonite and glauconite due to that during painting it produces the orientation of the layers of these minerals, responsible for an intensity increase of 001 reflection and decrease of the other reflections. The 060 reflection used for the differentiation of both minerals practically is not observable in our diagrams. The presence of other crystalline and amorphous phases coming from the support layer of the
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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Table 1 Chemical elements characterised by FXR portable directly on the fragments and by EDX on the cross-sections of group i) green colours. Sample 22.1 22.2 26 53 54 55 76.1 76.2 119 121.1 121.2
XRF analysis Ca(+)Cr,Fe,K,Ni,Sr,Ti Ca(+),Cr(+)Fe,K,Ni, Ca(+)Cr,Fe,K,Ni,Sr Ca(+)Cr,Fe,K,Mn,Ni,Sr,Ti Ca(+)Cr,Fe,K,Ni,Sr,Ti Ca(+)Cr,Fe,K,Ni,Sr Ca(+)Cr,Fe(+),K,Ni,Sr Ca(+)Cr,Fe,K,Ni,Sr
EDX analysis of green grains
EDX analysis of green grains containing Cr
Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si(+) Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si(+) Al,Ca,Fe,K,Mg, Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si(+) Al,Ca,Fe,K,Mg Al,Ca,Fe,K,Mg
Al,Cr(+),Fe,Mg,Si Al,Ca,Cr(+),Fe,Mg,Si,Ti,Zn Al.Cr(+),Fe,Mg Al,Ca,Cr(+)Fe,Mg,Si Al,Ca,Cr(+)Fe,Mg,Si Al(+),Ca,Cr(++)Fe(+),Mg,Si,Ti Al(+),Ca,Cr(+)Fe(+),Mg,Si Al,Ca,Cr(+),K,Mg,Si,Zn, Al(+),Ca,Cr(+),Fe(+),Mg,Zn, Al,Cr(+)Fe(+),K,,Mg,Si,Zn Al,Ca,Cr,Fe,K,Mg,Mn,Si(+)
studied fragment makes the differentiation of these two micas difficult. Other minerals have been detected in the X-ray diagrams; however, differences have been found between different samples. Only calcite was detected in some samples (Fig. 5d); in others calcite and quartz appeared, whereas in others calcite and dolomite with quartz and feldspars (Fig. 5b) were detected. These differences are attributed to the mortar used that will be discussed later in this work. FT-IR spectroscopy can be useful for the identification of glauconite and celadonite, particularly in the range of the spectra between 3400–3700 cm−1 and 950–1100 cm−1 (Moretto et al., 2011). Bands at 3601, 3556 and 3531 cm−1 are characteristic of the stretching of hydroxyl groups. The four absorption bands that appeared in the FTIR spectra (Fig. 6) of the samples of this group attributed to Si\O bond in plane (977 and 1074 cm−1) and perpendicular to the clay mineral layer (1105 cm−1) are characteristic of celadonite. Glauconite showed only a large band peak in the 1000 cm−1 in this range. Ions with octahedral coordination structure, particularly Fe3+, in celadonite and glauconite can be detected in the range between 500 and 430 cm− 1. The presence of Fe3+ in the mica studied in this sample was shown by the absorption bands at 494, 457 and 440 cm−1. The presence of water
was confirmed by the band at 1428 cm− 1. The absorption bands at 795 and 690 cm−1 can be attributed to the bonding of OH to octahedral cations in celadonite. This spectrum also showed the presence of carbonates, due to CaCO3 binders (e.g., bands centred at 1428, 873 and 712 cm−1). The Raman spectra of the samples of this group showed band peaks at 175 and 200 cm− 1. This two-peak feature is characteristic of celadonite. A peak at 277 cm−1 is also typical by celadonite. In glauconite, peaks at 263–268 cm−1 are typically found (Aliatis et al., 2009). All these experimental results imply the presence of celadonite as the green pigment in these fragments. In addition, chlorite and chromium oxide may also be responsible for the observed green colour. The additional spectroscopic investigation confirms the conclusions from chemical analysis that this green colour originates from Verona. 3.2. Group ii) The same procedure for characterisation of group i) has been applied to group ii). Because of the grinding of the pigment and the polishing of the paint layer, it is difficult to detect differences in morphology. Portable XRF, XRD and IR spectroscopy are also not easily interpreted due to the mixture of different minerals with similar compositions and in the presence of the calcite, which is used as a support and binder. Due to the spatial resolution of SEM–EDX and micro-Raman performed on the sample cross-sections, it was possible to differentiate between the different minerals present in the green pigments of the studied samples in this work. The cross sections observed using an optical microscope (i.e., Fig. 2e– h) showed important differences with the group i), appearing blue and green particles with angular morphology probably produced by grinding frits cakes to obtain the required shape (Hatton et al., 2008). Some samples showed high concentration of green particles and few particles of blue colour (Fig. 2e, f), while others showed a high proportion of these particles and others with morphology similar to showed in group i) (Fig. 2e). The chemical analysis of this group performed by EDX showed differences from the first group. A general analysis performed by EDX in the SEM showed the presence of Si, Al, Mg, K, Ca, Fe and Cu (Fig. 7a). The blue particles contained Si, Ca, Cu and O (Fig. 7c); other particles with morphology similar to group i) contained Si, Fe,
Table 2 Quantitative chemical analysis (%) carried out by punctual chemical analysis of green particles. Ratio atoms (%): Fe/Mg, Si/Al and K/(Si/Al) obtained from the quantitative analysis.
Fig. 4. EDX analysis of punctual chemical analysis of green grains from samples of group i).
SiO2 Al2O3 FeO MgO K2O Fe/Mg Si/Al K/(Si/Al)
59.5 4.90 18.5 8.19 9.10 2.91 10.74 0.5
58.3 5.00 19.3 10.3 7.15 2.41 10.32 0.41
57.0 5.39 19.21 11.1 7.30 2.22 9.21 0.47
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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Fig. 7. EDX analysis performed on cross-sections of samples of group ii). a) general analysis; b) analysis of blue particles and c) analysis of particles with similar morphology of group i).
Mg, Al and K, which are typical of mica (Fig. 7b). Ca was also found and attributed to calcite. However, Cr was not found; the portable XRF analysis did not show the presence of this element. A SEM image of the blue grains is shown in Fig. 8. The morphology shown is typical of a refractory material. Due to its colour and chemical composition, this mineral is thus attributed to the presence of Egyptian blue, which is considered to be one of the first synthetic pigments, first produced during the fourth Dynasty in Egypt and widely used in Roman period (Fitzhugh, 1997). The addition of Egyptian blue to the green earth to produce more brilliant colours was a common practice of the Roman wall painters (Mazzocchin et al., 2003). The cross-sections showed particles of blue and green colour. The blue colour showed the presence of Si, Ca and Cu characteristic of blue
Egyptian. However, the chemical analysis of green particles showed also the presence of Si, Ca and Cu although with different concentrations compared to the Egyptian blue (i.e. higher and lower concentration of Ca and Cu, respectively). The content of Ca was about 10% and 20% for blue and green Egyptian pigment, respectively. These results were in agreement with the data obtained by Hatton et al. (2008) that have found that the production of green frits have involved a reduction in the amount of copper added to the mixture compared to the added for Egyptian blue frits and an increase in the amount of alkali flux. The composition of the green particles was attributed to Egyptian green pigment, which is composed of the same chemical elements as Egyptian blue. In these samples, a mixture of both pigments (i.e., Egyptian blue and green pigment) was present and must be considered two entirely different pigments produced with different recipes (Pages-Camagna and Colinart, 2003; Schiegl and El Goresy, 2006; Hatton et al., 2008); the artist of the wall paintings likely mixed these two pigments to obtain the desired tonality.
Fig. 6. FTIR spectra of some samples of group i).
Fig. 8. SEM microphotography of Egyptian blue.
Fig. 5. X-ray diffraction performed on the surface of some fragments of group i) (C = calcite, Ch = chlorite, D = dolomite, Ox = iron oxide, Q = quartz, M = mica).
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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The XRD (Fig. 9) performed on the surface of these fragment by grazing angle incidence showed reflections at 7.58, 3.79, 3.36, 3.29, 3.00 Å, etc. and were attributed to cuprorivaite; however, the relative peak intensities found did not match the cuprorivaite JCPDS card (card 12-512) because of the preferred orientation of the mineral produced during the application on the wall painting by the artists due to its layer structure. Reflections at 10.00, 5.00, 4.45 and 3.33 Å were detected and can be attributed to the presence of mica (i.e., celadonite and/or glauconite). In addition, calcite, quartz, tridymite and feldspars were detected in the pigments of some fragments. However, the most important information obtained from these XRD diagrams were the presence of peaks that can be attributed to cuprorivaite present in the blue particles (i.e., Egyptian blue) according with the chemical analysis. However, the green colour of other particles and their chemical analysis showed also the presence of Egyptian green; the peaks showed by the XRD study may also be attributed to Egyptian green or wollastonite (Fig. 9). Both minerals cuprorivaite and wollastonite are difficult to distinguish by XRD using grazing angle incidence when they appear together due to the similarity of reflection of both minerals and due to the preferred orientation of both minerals. One small sample was taken from one fragment of this group and was treated with hydrochloric acid. The XRD diagram of the untreated sample is shown in Fig. 9e. Calcite appeared together with the other minerals previously characterised. The XRD diagrams of the treated sample (Fig. 9f) showed the presence of mica, cuprorivaite and/or wollastonite, quartz and tridymite more clearly. Tridymite is formed in the synthesis of the synthetic pigments Egyptian blue or Egyptian green. The presence of Sn (Fig. 4g) in some samples suggested that Cu was derived from bronze, while the absence of this element most likely suggested a different origin of the Cu, such as directly from ore deposits. The FTIR of these samples showed several absorption bands in 972–1105 cm−1, which can be attributed to a Si\O bond in plane and perpendicular to the silicate layers. The characterisation of celadonite
Fig. 9. X-ray diffraction performed on the surface of some fragments of group ii) (Ca = calcite, C = cuprorivaite, Ch = chlorite, D = dolomite, Q = quartz, M = mica, T = tridymite, W = wollastonite).
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and/or glauconite using these absorption bands in group ii) is difficult. In this range, the adsorption bands of these minerals and other absorption bands at 1011 and 1051 cm− 1, which overlap with the bands of Egyptian blue present in these samples, are shown. Raman spectroscopy has been used to distinguish celadonite and glauconite. The Raman spectra of these minerals showed bands between 100 and 300 cm−1 that correspond to the internal vibrations of the XO6 octahedral, where X is the interlayer metal. The bands between 200 and 800 cm−1 correspond to the vibration modes of SiO4 tetrahedral units. One Raman spectrum obtained in these samples is shown in Fig. 10. Bands at 175 and 215 cm− 1 are observable in celadonite, while the two peaks do not appear in glauconite, only showing a band between 180 and 200 cm−1. Thus, the doublet shown in this sample suggested the presence of celadonite. However, the intensity of the band at 215 cm−1 is smaller compared to the band showed by standard celadonite. Celadonite and glauconite show bands at 270 and 264 cm−1, respectively. In these spectra, a peak at 267 cm−1 is shown near the bands of both minerals. Bands at 385 and 400 cm− 1 are found in celadonite and glauconite, respectively. In the samples studied in this paper, a peak at 387 cm−1 is shown, which is very similar to the glauconite but is rather broad. In glauconite, the band at 590 cm−1 reaches maximum intensity, while in celadonite, the band at 550 cm−1 is the primary band. The spectra of the samples studied in this work showed both bands: one strong at 586 cm− 1, and the other strong at 548 cm−1. The laser power was controlled because excessive irradiation would lead to broad spectra with one band centred at 585 cm− 1 for both species (Ospitali et al., 2008). The peak that appeared at 700 cm−1 is found in both minerals. The small bands that appeared at 319, 357 and 456 cm−1 can also be attributed to glauconite (Ospitali et al., 2008). However, in several samples studied in this work, the peak at 456 cm−1 presented the maximum intensity. We considered that in this case, the presence of this peak with its high intensity can be attributed to the presence of Egyptian blue or green, which were detected in these samples by XRD and EDX. The small differences in the position and intensity of the peaks in the range between 100 and 300 cm− 1 together with the presence of the two peaks at 586 and 548 cm−1 suggested the presence of a mixture of celadonite and glauconite. The mixture of both minerals, despite their different origin, has also been found by Ospitali et al. (2008) in an archaeological site in Central Italy called Sussa (Ancona) and Pisaurum (Pesaro-Urbino). This technique confirms that in some fragment of the wall paintings studied, a pigment made from celadonite and glauconite was used; in some samples, a mixture with Egyptian blue and a mixture of Egyptian blue and Egyptian green were also present.
Fig. 10. Raman spectra performed on cross-sections of some samples of group ii).
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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3.3. Painting supports Painting supports were shown to vary in terms of the number of layers present and the relative coarseness of the mortars used, which will be referred to herein as “intonaco” (Piovesan et al., 2011). The paint was applied to the topmost of the layers (Rowland, 1999); in this work, we have studied this top layer. Chemical analysis was performed for both crystals (i.e., aggregate) and matrices (i.e., binders). Four classes of intonaco were found in the studied samples. A cross-section of the first group of intonaco is shown in Fig. 2i. The chemical analysis of the aggregates showed the presence of only Ca and small percentages of Si and Al. This aggregate consists of euhedral calcite crystal. The petrographic study showed a micrite-like matrix composed of crypto and microcrystalline calcite. The matrix is composed primarily of Ca with small amounts of Si, Al, K and sometimes Fe (Fig. 11a). These pieces of information confirmed the presence of calcite and silicates. The presence of euhedral calcite crystals also confirmed the presence of intonaco nominated marmorino. The aggregates of the second group (cross section in Fig. 2j) are completely different to the previous group. The chemical analysis showed the presence of Si, which can be attributed to fragments of quartz (Fig. 11b). The matrix showed a similar composition to that of the first group describe in this work. The aggregates of the third group (cross-section in Fig. 2k) showed another composition. The chemical analysis showed fragments with different chemical compositions that can be attributed to dolomite (Fig. 11c), feldspars (Fig. 11d) and quartz. The matrix is similar to those in the other studied samples. The cross-sections of three of the studied fragments showed two painting layers separated by a layer of white colour (cross-section in Fig. 2l). The white colour layer is composed of a calcite with lower porosity. These results confirmed that different aggregates have been used to create the intonaco. 4. Conclusions The green colour palette of the Roman wall paintings found in the Seville Alcazar excavation is consistent with that observed throughout the Roman Empire. Two groups of pigments have been found. The X-ray diffraction study did not allow the differentiation of celadonite and glauconite; however, mica and chlorite were characterised. The punctual chemical analysis performed by SEM–EDX, FTIR and Raman spectroscopy showed the presence of celadonite in the first group (i). The SEM–EDX study characterised particles composed of chromium that were not included
Fig. 11. EDX analysis performed in grains of different supports of the wall-painting.
in the octahedral coordination of the mica. Chlorite has also been detected in all studied samples of this group. The presence of this mineral and chromium oxide is also responsible for the observed green colour. The presence of celadonite and chromium in these pigments suggested that the green earth used in this group of Roman wall paintings was originated from caves near Verona. In the second group (ii) of the studied fragments, inexpensive pigments, such as green earth, mixed with precious pigments, such as Egyptian blue and Egyptian green has been identified. SEM–EDX provided the best characterisation of the mixture of Egyptian blue and Egyptian green; however, overlapping of the peaks of these two pigments in the XRD diagrams has hindered characterisation using this technique. Micro-Raman spectroscopy was the only technique that was able to distinguish the mixture of celadonite and glauconite present in the fragments of the second group. The presence of Sn in the two samples indicated that Cu was derived from bronze while the absence of this element most likely suggested a different origin of the Cu used, which may have been ore deposits. For the preparation layers, three different types of intonaco have been recognised based on the composition of their aggregate. The matrix is composed primarily of Ca with small amounts of Si, Al and sometimes K and Fe. White layer composed of calcite with lower porosity has been also found between two painting layers. All data and, in particular, the absence of trace amounts of organic binders and a carbonation layer suggested that the most utilised painting technique was fresco. In two samples, two layered coloured samples were found. The carbonation layer between the two differently coloured layers suggested that the superficial painting one was applied with a lime painting technique. Acknowledgements The authors are indebted to the Patronato de los Reales Alcazares de Sevilla for their collaboration with this investigation. The financial support of the CHARISMA — FP7 n. 228330, the Spanish Commission Interministerial de Ciencia y Tecnología (CICYT) under project BIA200912618 and the Junta de Andalucia (TEP-6558) is also acknowledged. Samples were provided by M.D. Robador, architect, and M.A. Tabales and A. Duran, archaeologists. References Aliatis, I., Bersani, D., Campani, E., Casoli, A., Lottici, P.P., Mantovan, S., Marino, I.-G., Ospitali, F., 2009. Green pigments of the Pompeian artista` palette. Spectrochim. Acta A Mol. Biomol. Spectrosc. 73, 532–538. Augusti, S.I., 1967. Colori Pompeiani. D Luca Editore, Rome. Bianchetti, P., Talarico, F., Vigliano, M.G., Ali, M.F., 2000. Production and characterization of Egyptian blue and Egyptian green frit. J. Cult. Herit. 1, 179–188. Brindley, G.W., Brown, G., 1980. Crystal Structures of Clay Minerals and Their X-ray Identification. Mineralogical Society, London. Canti, M.E., Heathcote, J.L., 2002. Microscopic Egyptian blue (synthetic cuprorivaite) from sediment at two archaeological sites in West Central England. J. Archaeol. Sci. 29, 831–836. Castellato, U., Vigato, P.A., Russo, U., Matteini, M., 2000. A Mösbauer approach to the physic-chemical characterization of iron containing pigments for historical wall paintings. J. Cult. Herit. 1, 217–232. Clementi, C., Ciocan, V., Vagnini, M., Doherty, B., Tabasso, M.L., Cunti, C., Brunetti, B.G., Miliani, C., 2011. Non-invasive and microdestructive investigation of the Domus Aurea wall painting decoration. Anal. Bioanal. Chem. 401, 1815–1826. Domenech-Carbo, M.T., Bosh-Reig, F., Gimeno Adelantado, J.V., Periz-Martinez, V., 1996. Fourier transform infrared spectroscopy and the analytical study of works of art for purposes of diagnosis and conservation. Anal. Chim. Acta 330, 207–215. Drits, V.A., Dainyak, L.G., Muller, A., 1997. Isomorphous cation distribution in celadonites, glauconites and Fe-illites determined by infrared, Mössbauer and EXAFS spectroscopies. Clay Miner. 32, 153–179. Duran, A., Jimenez de Haro, M.C., Perez-Rodriguez, J.L., Franquelo, M.L., Herrera, L.K., Justo, A., 2010. Determination of pigments and binder in Pompeian wall paintings using synchrotron radiation-high-resolution X-ray powder diffraction and conventional spectroscopy–chromatography. Archeometry 52, 286–307. Duran, A., Perez-Rodriguez, J.L., Jimenez de Haro, M.C., Franquelo, M.L., Robador, M.D., 2011. 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. J. Archaeol. Sci. 38, 2366–2377.
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J.L. Perez-Rodriguez et al. / Applied Clay Science xxx (2015) xxx–xxx Eastaugh, N., Walsh, V., Choplin, T., Siddald, 2004. The Pigment Compendium: A Dictionary of Historical Pigments. Elsevier, Amsterdam. Edrein, M.C., Feliu, M.J., Fernandez-Lorenzo, C., Marin, J., 2001. Spectroscopic study of Egyptian blue mixed with other pigments. Anal. Chim. Acta 434, 331–345. Fitzhugh, W., 1997. Artists' Pigments: A Handbook of Their History and Characterization vol. 3. University NY, Oxford. Genestar, C., Pons, C., 2005. Earth pigments in painting: characterization and differentiation by means of FTIR spectroscopy and SEM–EDS microanalysis. Anal. Bioanal. Chem. 382, 268–274. Gianoncelli, A., Castaing, J., Ortega, L., Doorhyées, E., Salomon, J., Walter, P., Hodeau, J.L., Bordet, P., 2008. A portable instrument for in situ determination of the chemical and phase composition of cultural heritage objects. X-ray Spectrom. 37, 418–423. Gliozzo, E., Cavari, F., Damiani, D., Memmi, 2012. Pigments and plasters from the Roman settlement of Thamusida (Rabat, Morocco). Archaeometry 54, 278–293. Grissom, C.A., 1986. Green earth. In: Feller, R. (Ed.), Artists' Pigments vol. 1. Cambridge University Press, UK, pp. 141–167. Grygar, T., Hradil, D., Hradilova, J., Hradil, D., Bezdicka, P., Bakardjeva, S., 2003. Analysis of earthy pigments in grounds of Barroque paintings. Anal. Bioanal. Chem. 375, 1154–1160. Hatton, G.D., Shortland, A.J., Tite, M.S., 2008. The production technology of Egyptian blue and green frits from second millennium BC Egypt and Mesopotamia. J. Archaeol. Sci. 35, 1591–1604. Hradil, D., Grygar, T., Hradilova, J., Bezdicka, P., 2003. Clay and iron oxide pigments in the history of painting. Appl. Clay Sci. 22, 223–236. Hradil, D., Grygar, T., Hruskova, M., Bezdicka, P., Lang, K., Schneeweiss, O., Chvatal, M., 2004. Green earth pigment from the Kadan Region, Czech Republic: use of rare Ferich smectite. Clay Clay Miner. 52, 767–778. Hradil, D., Pisková, A., Hradilová, J., Bezdicka, P., Lehrberger, G., Gerzer, S., 2011. Mineralogy of Bohemian green earth pigment and its microanalytical evidence in historical paintings. Archaeometry 53, 563–586. Jaksch, H., Seipel, W., Weiner, K.L., El Grresy, A., 1983. Egyptian blue, cuprorivaite. A Window to Ancient Egyptian Technology Die Naturwissenschaften 70 pp. 525–535. Kaczmarczyk, A., Hedges, R.E., 1983. Ancient Egyptian Faience — An Analytical Survey of Egyptian Faience From Predynastic to Roman Times. Aries and Phillips, Warminster, U.K. Khandekar, N., 2003. Preparation of cross-section from easel paintings. Rev. Conserv. 4, 52–64. Maggiolaro, V., Molin, G., Pappalardo, U., Vergerio, P., 1997. Proceeding of the International Workshop on Roman Wall Painting, Fribourg 1997, pp. 105–117. Mazzocchin, G.A., Agnoli, F., Mazzocchim, S., Colpo, I., 2003. Analysis of pigments from Roman wall paintings found in Vicenza. Talanta 61, 565–572. Moretto, L.M., Orsega, E.F., Mazzocchin, G.A., 2011. Spectroscopic methods for the analysis of celadonite and glauconite in Roman green wall paintings. J. Cult. Herit. 12, 384–391. Ospitali, F., Bersani, D., Di Lionardo, G., Lottici, P.P., 2008. Green earth: vibrational and elemental characterization of glauconites, celadonites and historical pigments. J. Raman Spectrosc. 39, 1066–1073.
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Pages-Camagna, S., Colinart, S., 2003. The Egyptian green pigments: its manufacturing process and links to Egyptian blue. Archeometry 45, 637–658. Pages-Camagna, S., Laval, E., Vigears, D., Duran, A., 2010. Non-destructive and in situ analysis of Egyptian wall paintings by X-ray diffraction and X-ray fluorescence portable systems. Appl. Phys. A 100, 671–681. Piovesan, R., Siddall, R., Mazzoli, C., Nodari, L., 2011. The Temple of Venus (Pompeii): a study of the pigments and painting techniques. J. Archeol. Sci. 38, 2633–2643. Pliny, 1968. Natural History in Ten Volumes, Vol. XI. In: Rackham (Ed.), Books XXXIII– XXXV. Loel Classical Library, Cambridge MA. Rafalska-Lasocha, A., Kaszowska, W., Dziembaj, R., 2010. X-ray powder diffraction investigation of green earth pigments. Powder Diffract. 25, 38–45. Rieder, M., Cavazzini, G., D'yakonov, Y.S., Frank-Kamenetskii, V.A., Gottandi, G., Guggenheim, S., Koval, P.V., Müller, G., Neiva, A.M.R., Rodoslovich, E.W., Robert, L.L., Sassi, F.P., Takeda, H., Weiss, Z., Wones, D.R., 1998. Nomenclature of the micas. Can. Mineral. 36, 905–912. Rowland, I.D., 1999. (Vitruvius the Ten Books on Architecture). Cambridge University Press. Vitruvius (1st cent BC/Rouland 1999). Schiegl, S., El Goresy, A., 2006. Comments on S. Pages-Camagna and S. Colinart. “The Egyptian green pigments: its manufacturing process and links to Egyptian blue”. Archeometry 45 (4) (2003), 637–58. Archaeometry 48 (4), 707–713. Schiegl, S., Weiner, K.L., El Goresy, A., 1992. The diversity of newly discovered deterioration patterns in ancient Egyptian pigments, consequences to entirely new restoration strategies and to the egyptological colour symbolism. Mater. Res. Soc. Symp. Proc. 267, 831–838. Singer, C., Holmyard, E.J., Hall, A.R. (Eds.), 1954. A History of Technology. Claredon Press, Oxford. Tabales, M.A., 2010. Summary of the Archeological Works Carried Out in 2009 in Patio de Banderas. Apuntes del Alcazar de Sevilla. Patronato del Real Alcazar. Technographic, Sevilla, pp. 135–145. Tabales, M.A., 2012. The subsoil of the Patio de Banderas between 9th centuries BC and 12th AD. In: de Sevilla, Alcazar (Ed.), Archaelogical Investigations in the Alcazar of Seville Campaigns 2009–2012. Apuntes del Alcazar de Seville, pp. 1–28. Ulrich, D., 1987. Egyptian blue and green frit: characterization, history and occurrence, synthesis. Datation-Caracterisation des painters parietals et murals, Ravello, Part 17pp. 324–332. Usman, M., Hanna, K., Abdelmoula, M., Ruby, C., 2012. Formation of green rut via mineralogical transformation of ferric oxides (ferrihydrite, goethite and hematite). Appl. Clay Sci. 64, 38–43. Valanciene, V., Siauciunas, R., Valancius, Z., 2014. Evaluation of glauconite rock color stability during firing. Appl. Clay Sci. 99, 110–118. Vitruvius, 1999. Ten Books on Architecture. Cambridge University Press, Cambridge/New York.
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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Research paper
Green pigments of Roman mural paintings from Seville Alcazar Jose Luis Perez-Rodriguez ⁎, Maria del Carmen Jimenez de Haro, Belinda Siguenza, José María Martinez-Blanes Materials Science Institute of Seville (CSIC-Seville University), Americo Vespucio 49, 41092 Seville, Spain
a r t i c l e
i n f o
Article history: Received 6 January 2015 Received in revised form 14 March 2015 Accepted 17 March 2015 Available online xxxx Keywords: Roman wall painting Celadonite Glauconite Egyptian blue Egyptian green Support
a b s t r a c t We report here a study of 30 fragments of green wall paintings from Roman times found in the Patio de Banderas excavation in Seville Alcazar. The sample characterisation was realised using optical microscopy, colourimetry, infrared and micro-Raman spectroscopy, X-ray diffraction, and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. The study of these pigments is important because it can help determine the source or the pictorial technique used. The samples studied in this work have been divided into two groups, according to the composition of their green pigments. In the first group, celadonite has been characterised as the primary component of the green colour; chlorite was also detected. Particles constituted by chromium accompanied by aluminium, iron and zinc were found in all studied samples of this group. Chlorite and chromium oxide could also be responsible for the green colour. The presence of chromium suggested the presence of green colour pigment from Verona. In the second group, a mixture of celadonite and glauconite was detected and could be responsible for the green colour observed. The addition of refracting material such as Egyptian blue was also used. A mixture of Egyptian green and Egyptian blue together with celadonite and glauconite was also found. Four classes of intonaco were recognised and classified based upon the composition of the aggregates. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The archaeological excavation of the Patio de Banderas was performed by Tabales (2010, 2012), and was organised by the Foundation of the Reales Alcazares of Seville to obtain information about the stratigraphy of the first enclosure of the Real Alcazar. The Patio de Banderas excavations found remains belonging to the Early Iron Age and structures belonging to ancient Roman buildings, the most important of which was the one raised by the opus africanum technique. A large building from the end of the fifth century built around a columned courtyard was also found; this building perhaps belonged to religious units linked to a church outside the walls. The most important of the excavated Roman buildings belonged to the beginnings of Roman urbanism during the republican phase I (circa 100 BC), the republican phase 2 (60–30 BC) and reforms of the imperial period (1st and 2nd centuries AD). Coatings in situ have not survived but many polychrome fragments in the imperial levels have, dating to the late republican time and for the first imperial time, richly decorated interiors with quality plastering. Paintings and colour remains from Roman Ages have been discovered and studied for over a century. Roman artists had a wide knowledge of green pigment, including verdigris, malachite and green earth (Singer et al., 1954; Eastaugh et al., 2004). Important discoveries were performed in Pompei and Rome (Mazzocchin et al., 2003; Aliatis et al., 2009; Duran et al., 2011; Piovesan et al., 2011). In Spain, scientific
⁎ Corresponding author. Tel.: +34 954489532. E-mail address: [email protected] (J.L. Perez-Rodriguez).
research in archaeological finds has been developing (DomenechCarbo et al., 1996; Edrein et al., 2001; Duran et al., 2010). Other Roman wall paintings from other countries have also been studied (Maggiolaro et al., 1997; Gliozzo et al., 2012). Malachite ores came from Armenia, Cyprus, Macedonia and Spain. The one from Armenia was the most precious pigment (Augusti, 1967; Pliny, 1968; Vitruvius, 1999; Aliatis et al., 2009). Pliny (1968) mentioned that malachite was a rare and expensive material that was also called chrysocolla, which is the name now used for hydrated copper silicate. Green earth (i.e., creta viridis or appianium in ancient times) was typically used in wall paintings since ancient times and is still used (Grissom, 1986; Grygar et al., 2003; Hradil et al., 2003). The minerals responsible for the colour of green earth are types of clay micas, glauconite ((K0.8Na0.01Ca0.04)(Fe3+1.31Al0.28Mg0.4)(Si3.58Al042)4O10(OH)2 and celadonite ((K0.94)(Fe3 +0.72Al0.42Mg0.6Fe2 +0.24(Si3.9Al0.1)4O10(OH)2 (Rieder et al., 1998). Also smectite, chlorite, serpentines and pyroxenes can be responsible of this colour (Grissom, 1986; Hradil et al., 2003, 2004; Usman et al., 2012; Valanciene et al., 2014). Glauconite and celadonite have similar compositions but are formed under different geological conditions: celadonite is found in amigdules or fractures in metamorphic rocks, while glauconite is found in the form of small greenish pellets (i.e., green sand) in shallow marine sedimentary rock (Ospitali et al., 2008). Both minerals consist of a layer of octahedral coordinated cations (Al, Fe3+, Fe2+ and Mg), sandwiched between two sheets of silicium tetrahedral and have small tetrahedral substitutions; an interlayer of K ions holds the layers together (Brindley and Brown, 1980). Celadonites and glauconites have been studied by numerous methods (Drits et al., 1997) and are typically found as dull grey-green
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Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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to bluish green masses. Mineralogical analyses in the field of cultural heritage are rare and often limited to the identification of the generic class “green earth” without specific characterisation of the mineralogical species present in the artefacts. The most famous deposits of green earth can be found near Verona, Italy, as well as in Tyrol, Bohemia, Saxony, Poland, Hungary, France, Cyprus and England. Verona earth is constituted by celadonite found in basaltic rocks. However, the presence of glauconite cannot be excluded from a green pigment because it can be found in sand stone levels as a result of mixing between extrusive tertiary products with eocenic sediments (Aliatis et al., 2009). The similarity in the structure and composition of glauconite and celadonite makes its analytical distinction difficult. In this study, we were not able to positively distinguish glauconite from celadonite; however, different experimental techniques have been used to distinguish both minerals used in Roman wall paintings; these techniques include Móssbauer (Castellato et al., 2000), Raman and EDS (Moretto et al., 2011), XRD (Rafalska-Lasocha et al., 2010), FT-IR, EDS, AAS spectrophotometric analysis, EPR, and micro-Raman spectroscopy (Genestar and Pons, 2005; Ospitali et al., 2008; Clementi et al., 2011; Moretto et al., 2011). In a recent work, Duran et al. (2011) detected glauconite but not celadonite in some wall painting samples of different colours from Pompei and Herculaneum by synchrotron radiation-high-resolution powder diffraction (SH-HRPD). A common practice of Roman wall painters was the addition of Egyptian blue to green earth to produce more brilliant colours (Mazzocchin et al., 2003). Egyptian craftsmen created a blue pigment (i.e., Egyptian blue) by firing a mixture of compounds containing silicon, calcium and copper with a soda or plant-derived potash as a flux at 850–1000 °C. This technology was lost after the seventh century (Pages-Camagna and Colinart, 2003). The characterisation of this pigment in ancient times has been widely studied (Mazzocchin et al., 2003; Eastaugh et al., 2004; Pages-Camagna et al., 2010; Clementi et al., 2011; Duran et al., 2011; Piovesan et al., 2011). The green colour could also be obtained from the mixture of Egyptian blue with a yellow pigment or this mixture could be added to other green pigment, such as malachite or green earth, to obtain a darker colour (Clementi et al., 2011). A pigment with the same chemical elements as Egyptian blue called Egyptian green with a turquoise colour was also used. This pigment is also called green frit (Ulrich, 1987; Schiegl et al., 1992). It has been considered to be a misfired Egyptian blue (Jaksch et al., 1983; Ulrich, 1987); the colour has also been interpreted to indicate the presence of iron coming from the sand (Kaczmarczyk and Hedges, 1983) or a weathered Egyptian blue. The alteration of this pigment generates only copper carbonate or copper chloride. However, the Egyptian blue and Egyptian greens are two entirely different pigments produced following different recipes (Bianchetti et al., 2000; Pages-Camagna and Colinart, 2003; Schiegl and El Goresy, 2006). The Egyptian green pigment is produced from the same components of the Egyptian blue simply changing the concentration and temperature conditions to obtain a glassy phase where Cu2+ occupied an octahedral coordination and consequently a green colour (Eastaugh et al., 2004). The colour tone of the Egyptian green pigment should depend on the origin of copper impurities in the sand and manufacturing temperature (Canti and Heathcote, 2002). The goal of the present work was the study of the green colour of several fragments from the Patio de Banderas excavation. The identification and study of these pigments used in Roman wall paintings found in this excavation will obtain information on the technique used by Roman. This study can provide to the archaeologists and art historians precise information on the technique used in the creation of the work itself. In addition, the results can provide conservators and restorers with guidelines on the materials necessary for conservation. This work was focused on the characterisation of glauconite and celadonite and the techniques on these wall paintings, which included non-invasive methodologies integrated by focused micro-invasive analysis. This work was also focused on the characterisation of Egyptian blue
and green mixture with celadonite and/or glauconite. This identification could help trace possible routes of Roman painting in Spain. 2. Experimental 2.1. Materials 30 green coloured fragments from the Patio de Banderas supplied by Professors Tabales and Duran of Seville University were analysed. The interest for the study has been described by Tabales, 2012. Fig. 1 shows several fragments of the samples studied in this work. The fragments were buried; the samples were in excellent conditions and were not subjected to any previous restoration processes. The size of the samples was variable (dimensions of 12 cm × 7 cm to 3.5 cm × 1.5 cm.) The thickness of the fragments ranged from 3 cm to 0.9 cm including the mortar and pictorial layer. The cross sections were prepared from small samples taken from the wall painting fragments following the previously described methodology (Khandekar, 2003). 2.2. Techniques 2.2.1. Colourimetric analysis Colour measurements were performed on the samples with a Dr. Lange Micro Color Labor station. Experimental data were recorded according to the CIE (Commission International De L' Éclairage); lightness L*, red-green coordination a* and yellow-blue coordinate b*. 2.2.2. Optical microscopy The cross-sections were prepared starting from a mould of methyl polymethacrylate where the samples were placed horizontally and refilled up with epoxy resin of methylmethacrylate. The resulting material was cut with a fretsaw equipped with a Bahco 302-835-blade, which was polished with an automatic polishing machine and various grades of sand paper and was finished with a cloth. The cross sections were observed and photographed using a Nikon OPTIPHOT (× 25, × 50 and ×100) optical microscope. Fig. 2 shows a selection of the cross sections prepared from the extracted samples. The thickness of the colour layers ranged from 3 μm to 25 μm. 2.2.3. Micro-Raman laboratory equipment The integrated dispersive Horiba Jobin Yvon LabRaman system was used to record the Raman spectra. These experiments were performed directly on the artwork or on the cross sections. Two external visible diode lasers with a solid-state source are available in this apparatus: 532.14 nm (green) and 784.56 nm (red). However, we primarily used the 784 nm source to minimise fluorescence from the organic medium or from the pigments/dyes themselves. The instrument has a chargecoupled device (CCD) detector and a grating of 600 grooves/mm. A confocal optical microscope is coupled to the Raman spectrometer. The majority of the measurements presented in this paper were collected at 100× magnification. The size of the analysed zones depends on the microscope magnification. At 100 ×, the spot sizes were 0.72 μm and 1.06 μm for the green and red lasers, respectively, and the spatial resolution was 0.53 μm. Each Raman spectrum was recorded for 8–12 min with a spectral resolution of 2 cm− 1. The standard spectrum was obtained from the Jobin Yvon Commercial Databases: www.horiba. com/scientific/products/raman-spectroscopy/accesories/raman-spectrallibraries (ancient pigments). 2.2.4. Fourier transform infrared spectroscopy (FTIR) The Fourier transform infrared study was performed using a Jasco FTIR 6200. Small samples were ground, and a disk with KBr was prepared.
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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Fig. 1. Several fragments of the samples studied in this work.
Fig. 2. Selection of the cross sections prepared from the extracted samples. Group i) a–d. Group ii) e–h. Painting supports i–l.
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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2.2.5. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM–EDX) Elemental chemical analyses of the cross sections were obtained using a HITACHI S-4800 SEM instrument equipped with a Bruker XFlash Detector 4010 EDX analyser at an accelerating voltage of 20 kV. The EDX quantitative microanalyses were obtained using the ZAF method of correction.
According to the mineralogical composition obtained in this work, the green pigments characterised have been divided into two groups: i): green colour was only observed in this group, representative crosssections are shown in Fig. 2a, b, c and d, and ii) mixture of blue and green colours was observed in this group, representative crosssections are shown in Fig. 2e, f, g and h. The fragments of both groups were found in different zones of the excavation.
2.2.6. X-ray diffraction (XRD) Grazing incidence XRD was used to study the surface of the fragments. The irradiated surface was 20 mm × 1.5 mm. X-ray powder diffraction was performed on a PANalytical X'PERT Pro MPD diffractometer with lambda = 1.540509 Å at 45 kV and 40 mA. A Pixcel solid-state detector was used. The study was performed directly on the fragments using XRD. Conventional XRD was also performed with the same equipment on ground small samples.
3.1. Group i)
2.2.7. Portable X-ray fluorescence (XRF) In-situ measurements were also performed using a portable XRF system (Gianoncelli et al., 2008). An X-ray tube (40 kV, 700 μA) with a copper anode was used. The XRF detector was a silicon drift detector (Röntec GmBH) and had an active area of 5 mm2 and a full width at half-maximum (FWHM) of 150 eV at 5.9 keV. It was Peltier-cooled to −10 °C and was located at 90° to the X-ray tube and on the axis normal to the analysed sample surface. At the exit of the tube, we used a slit of 0.5 mm; therefore, the measured area was approximately 9 mm2. The chemical analysis performed by portable XRF yields information of the external composition of the sample. For XRF, the depth of analysis depends on the nature of the chemical elements and the energy of the X-rays used for the detection of the elements. 3. Results and discussion Colorimetric analysis of the green colour surface of the fragments studied was accomplished by considering the L⁎ a⁎ b⁎ colour space. The lightness L⁎ values and saturation C are not given because they depended on the paint techniques and on the influence of the white colour used as a binder and support material. The relationship between a⁎ and b⁎ is shown in Fig. 3. A high heterogeneity of chromatic values was found in each area of green colour. The heterogeneity of the green colours was most likely due to the different colours near or under them. In some fragments, 4 green colours with different hues in the same colour area were found to be made with the same pigment but with different percentages of the pigment and binder. In other samples, mixtures between different green and blue pigments were detected. This technique was not able to differentiate between celadonite and glauconite, as described by Moretto et al. (2011).
Fig. 3. Representation of a⁎ (red-green coordination) versus b⁎ (yellow-blue coordinate) parameters of colourimetric analysis.
The chemical analysis performed by portable XRF is shown in Table 1. Ca(+), Cr, Fe, K, Ni, Ti, and Sr have been detected in these samples. These data suggested the presence of green earth. The most important information obtained was the presence of chromium that will help elucidating the source of this pigment. Despite its portability and facility in analysis and handling data, XRF is not the most powerful technique for obtaining information of all layers of a cross-section due to its thickness; thus, XRF was not adequate to distinguish the distribution of different layer analysed. In this work, the SEM–EDX performed on the cross-sections (i.e. Fig. 2a–d) helped complete the characterisation of different particles and distribution of the different layers. In Table 1, chemical analyses of green grains are shown. The chemical analysis of some grains showed the presence of chromium. The punctual chemical analysis of other green grains showed the presence of Si, Al, Mg, Fe, K and Ca (Fig. 4a), which suggested the presence of celadonite and/or glauconite. Due to the high resolution of SEM–EDX, it is possible to differentiate between different components present, including glauconite and celadonite. Based on the ratio Si:Al:Mg, it is possible to differentiate glauconite from celadonite: when Si N Al N Mg, glauconite is present; however, in celadonite, Si N Mg N Al. The quantitative chemical analyses performed by punctual chemical analysis and the atoms % Fe/Mg and K/ (Si/Al) of green particles is shown in Table 2. The compositions are similar to the stoichiometric composition of celadonite. The representation of Fe/Mg versus K/(Si/Al) showed that it is possible to include this samples in the celadonite field from Verona based on the study performed by Hradil et al. (2011). In all samples, particles of Cr (see Fig. 4b–d, f) were detected. In addition, this chemical element was accompanied by Fe (Fig. 4b), Al (Fig. 4c), Ti (Fig. 4d) and Si (Fig. 4f); Zn and Ca were also detected. Particles constituted primarily by Si were also found (Fig. 4e). It is known from the literature that terra verte may contain chromium oxide and cobalt–aluminium, which make a pigment green (Hradil et al., 2004). However, chromium is only present in green earth from Verona. These results confirm that the green earth is constituted by celadonite and that the pigment originated from Verona. The presence of particles made primarily of Cr suggests that this element is not included in the structure of mica (i.e., celadonite) and appeared as chromium oxide with the mica. Chromium oxides are also green in colour, which may imply that they are responsible for the colour of this pigment. The XRD analyses performed on the surface of the fragments (Fig. 5) indicated the presence of mica (Fig. 5b) (i.e., celadonite and/or glauconite). In some of these samples, reflections at 14.00, 7.05, 3.74 Å, etc. (Fig. 5a) also appeared and may be attributed to the presence of chlorite, which is also green in colour. The XRD diagrams obtained in these samples after acid treatment confirmed the presence of chlorite. In a fragment with a dark and light green colour the only differences found were the percentages of the green pigments (i.e., mica and chlorite) (see Fig. 5c and d). Iron oxides were also characterised (Fig. 5a, b). The XRD performed by grazing angle incidence do not allow a clear differentiation of celadonite and glauconite due to that during painting it produces the orientation of the layers of these minerals, responsible for an intensity increase of 001 reflection and decrease of the other reflections. The 060 reflection used for the differentiation of both minerals practically is not observable in our diagrams. The presence of other crystalline and amorphous phases coming from the support layer of the
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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Table 1 Chemical elements characterised by FXR portable directly on the fragments and by EDX on the cross-sections of group i) green colours. Sample 22.1 22.2 26 53 54 55 76.1 76.2 119 121.1 121.2
XRF analysis Ca(+)Cr,Fe,K,Ni,Sr,Ti Ca(+),Cr(+)Fe,K,Ni, Ca(+)Cr,Fe,K,Ni,Sr Ca(+)Cr,Fe,K,Mn,Ni,Sr,Ti Ca(+)Cr,Fe,K,Ni,Sr,Ti Ca(+)Cr,Fe,K,Ni,Sr Ca(+)Cr,Fe(+),K,Ni,Sr Ca(+)Cr,Fe,K,Ni,Sr
EDX analysis of green grains
EDX analysis of green grains containing Cr
Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si(+) Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si(+) Al,Ca,Fe,K,Mg, Al,Ca,Fe,K,Mg,Si Al,Ca,Fe,K,Mg,Si(+) Al,Ca,Fe,K,Mg Al,Ca,Fe,K,Mg
Al,Cr(+),Fe,Mg,Si Al,Ca,Cr(+),Fe,Mg,Si,Ti,Zn Al.Cr(+),Fe,Mg Al,Ca,Cr(+)Fe,Mg,Si Al,Ca,Cr(+)Fe,Mg,Si Al(+),Ca,Cr(++)Fe(+),Mg,Si,Ti Al(+),Ca,Cr(+)Fe(+),Mg,Si Al,Ca,Cr(+),K,Mg,Si,Zn, Al(+),Ca,Cr(+),Fe(+),Mg,Zn, Al,Cr(+)Fe(+),K,,Mg,Si,Zn Al,Ca,Cr,Fe,K,Mg,Mn,Si(+)
studied fragment makes the differentiation of these two micas difficult. Other minerals have been detected in the X-ray diagrams; however, differences have been found between different samples. Only calcite was detected in some samples (Fig. 5d); in others calcite and quartz appeared, whereas in others calcite and dolomite with quartz and feldspars (Fig. 5b) were detected. These differences are attributed to the mortar used that will be discussed later in this work. FT-IR spectroscopy can be useful for the identification of glauconite and celadonite, particularly in the range of the spectra between 3400–3700 cm−1 and 950–1100 cm−1 (Moretto et al., 2011). Bands at 3601, 3556 and 3531 cm−1 are characteristic of the stretching of hydroxyl groups. The four absorption bands that appeared in the FTIR spectra (Fig. 6) of the samples of this group attributed to Si\O bond in plane (977 and 1074 cm−1) and perpendicular to the clay mineral layer (1105 cm−1) are characteristic of celadonite. Glauconite showed only a large band peak in the 1000 cm−1 in this range. Ions with octahedral coordination structure, particularly Fe3+, in celadonite and glauconite can be detected in the range between 500 and 430 cm− 1. The presence of Fe3+ in the mica studied in this sample was shown by the absorption bands at 494, 457 and 440 cm−1. The presence of water
was confirmed by the band at 1428 cm− 1. The absorption bands at 795 and 690 cm−1 can be attributed to the bonding of OH to octahedral cations in celadonite. This spectrum also showed the presence of carbonates, due to CaCO3 binders (e.g., bands centred at 1428, 873 and 712 cm−1). The Raman spectra of the samples of this group showed band peaks at 175 and 200 cm− 1. This two-peak feature is characteristic of celadonite. A peak at 277 cm−1 is also typical by celadonite. In glauconite, peaks at 263–268 cm−1 are typically found (Aliatis et al., 2009). All these experimental results imply the presence of celadonite as the green pigment in these fragments. In addition, chlorite and chromium oxide may also be responsible for the observed green colour. The additional spectroscopic investigation confirms the conclusions from chemical analysis that this green colour originates from Verona. 3.2. Group ii) The same procedure for characterisation of group i) has been applied to group ii). Because of the grinding of the pigment and the polishing of the paint layer, it is difficult to detect differences in morphology. Portable XRF, XRD and IR spectroscopy are also not easily interpreted due to the mixture of different minerals with similar compositions and in the presence of the calcite, which is used as a support and binder. Due to the spatial resolution of SEM–EDX and micro-Raman performed on the sample cross-sections, it was possible to differentiate between the different minerals present in the green pigments of the studied samples in this work. The cross sections observed using an optical microscope (i.e., Fig. 2e– h) showed important differences with the group i), appearing blue and green particles with angular morphology probably produced by grinding frits cakes to obtain the required shape (Hatton et al., 2008). Some samples showed high concentration of green particles and few particles of blue colour (Fig. 2e, f), while others showed a high proportion of these particles and others with morphology similar to showed in group i) (Fig. 2e). The chemical analysis of this group performed by EDX showed differences from the first group. A general analysis performed by EDX in the SEM showed the presence of Si, Al, Mg, K, Ca, Fe and Cu (Fig. 7a). The blue particles contained Si, Ca, Cu and O (Fig. 7c); other particles with morphology similar to group i) contained Si, Fe,
Table 2 Quantitative chemical analysis (%) carried out by punctual chemical analysis of green particles. Ratio atoms (%): Fe/Mg, Si/Al and K/(Si/Al) obtained from the quantitative analysis.
Fig. 4. EDX analysis of punctual chemical analysis of green grains from samples of group i).
SiO2 Al2O3 FeO MgO K2O Fe/Mg Si/Al K/(Si/Al)
59.5 4.90 18.5 8.19 9.10 2.91 10.74 0.5
58.3 5.00 19.3 10.3 7.15 2.41 10.32 0.41
57.0 5.39 19.21 11.1 7.30 2.22 9.21 0.47
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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Fig. 7. EDX analysis performed on cross-sections of samples of group ii). a) general analysis; b) analysis of blue particles and c) analysis of particles with similar morphology of group i).
Mg, Al and K, which are typical of mica (Fig. 7b). Ca was also found and attributed to calcite. However, Cr was not found; the portable XRF analysis did not show the presence of this element. A SEM image of the blue grains is shown in Fig. 8. The morphology shown is typical of a refractory material. Due to its colour and chemical composition, this mineral is thus attributed to the presence of Egyptian blue, which is considered to be one of the first synthetic pigments, first produced during the fourth Dynasty in Egypt and widely used in Roman period (Fitzhugh, 1997). The addition of Egyptian blue to the green earth to produce more brilliant colours was a common practice of the Roman wall painters (Mazzocchin et al., 2003). The cross-sections showed particles of blue and green colour. The blue colour showed the presence of Si, Ca and Cu characteristic of blue
Egyptian. However, the chemical analysis of green particles showed also the presence of Si, Ca and Cu although with different concentrations compared to the Egyptian blue (i.e. higher and lower concentration of Ca and Cu, respectively). The content of Ca was about 10% and 20% for blue and green Egyptian pigment, respectively. These results were in agreement with the data obtained by Hatton et al. (2008) that have found that the production of green frits have involved a reduction in the amount of copper added to the mixture compared to the added for Egyptian blue frits and an increase in the amount of alkali flux. The composition of the green particles was attributed to Egyptian green pigment, which is composed of the same chemical elements as Egyptian blue. In these samples, a mixture of both pigments (i.e., Egyptian blue and green pigment) was present and must be considered two entirely different pigments produced with different recipes (Pages-Camagna and Colinart, 2003; Schiegl and El Goresy, 2006; Hatton et al., 2008); the artist of the wall paintings likely mixed these two pigments to obtain the desired tonality.
Fig. 6. FTIR spectra of some samples of group i).
Fig. 8. SEM microphotography of Egyptian blue.
Fig. 5. X-ray diffraction performed on the surface of some fragments of group i) (C = calcite, Ch = chlorite, D = dolomite, Ox = iron oxide, Q = quartz, M = mica).
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The XRD (Fig. 9) performed on the surface of these fragment by grazing angle incidence showed reflections at 7.58, 3.79, 3.36, 3.29, 3.00 Å, etc. and were attributed to cuprorivaite; however, the relative peak intensities found did not match the cuprorivaite JCPDS card (card 12-512) because of the preferred orientation of the mineral produced during the application on the wall painting by the artists due to its layer structure. Reflections at 10.00, 5.00, 4.45 and 3.33 Å were detected and can be attributed to the presence of mica (i.e., celadonite and/or glauconite). In addition, calcite, quartz, tridymite and feldspars were detected in the pigments of some fragments. However, the most important information obtained from these XRD diagrams were the presence of peaks that can be attributed to cuprorivaite present in the blue particles (i.e., Egyptian blue) according with the chemical analysis. However, the green colour of other particles and their chemical analysis showed also the presence of Egyptian green; the peaks showed by the XRD study may also be attributed to Egyptian green or wollastonite (Fig. 9). Both minerals cuprorivaite and wollastonite are difficult to distinguish by XRD using grazing angle incidence when they appear together due to the similarity of reflection of both minerals and due to the preferred orientation of both minerals. One small sample was taken from one fragment of this group and was treated with hydrochloric acid. The XRD diagram of the untreated sample is shown in Fig. 9e. Calcite appeared together with the other minerals previously characterised. The XRD diagrams of the treated sample (Fig. 9f) showed the presence of mica, cuprorivaite and/or wollastonite, quartz and tridymite more clearly. Tridymite is formed in the synthesis of the synthetic pigments Egyptian blue or Egyptian green. The presence of Sn (Fig. 4g) in some samples suggested that Cu was derived from bronze, while the absence of this element most likely suggested a different origin of the Cu, such as directly from ore deposits. The FTIR of these samples showed several absorption bands in 972–1105 cm−1, which can be attributed to a Si\O bond in plane and perpendicular to the silicate layers. The characterisation of celadonite
Fig. 9. X-ray diffraction performed on the surface of some fragments of group ii) (Ca = calcite, C = cuprorivaite, Ch = chlorite, D = dolomite, Q = quartz, M = mica, T = tridymite, W = wollastonite).
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and/or glauconite using these absorption bands in group ii) is difficult. In this range, the adsorption bands of these minerals and other absorption bands at 1011 and 1051 cm− 1, which overlap with the bands of Egyptian blue present in these samples, are shown. Raman spectroscopy has been used to distinguish celadonite and glauconite. The Raman spectra of these minerals showed bands between 100 and 300 cm−1 that correspond to the internal vibrations of the XO6 octahedral, where X is the interlayer metal. The bands between 200 and 800 cm−1 correspond to the vibration modes of SiO4 tetrahedral units. One Raman spectrum obtained in these samples is shown in Fig. 10. Bands at 175 and 215 cm− 1 are observable in celadonite, while the two peaks do not appear in glauconite, only showing a band between 180 and 200 cm−1. Thus, the doublet shown in this sample suggested the presence of celadonite. However, the intensity of the band at 215 cm−1 is smaller compared to the band showed by standard celadonite. Celadonite and glauconite show bands at 270 and 264 cm−1, respectively. In these spectra, a peak at 267 cm−1 is shown near the bands of both minerals. Bands at 385 and 400 cm− 1 are found in celadonite and glauconite, respectively. In the samples studied in this paper, a peak at 387 cm−1 is shown, which is very similar to the glauconite but is rather broad. In glauconite, the band at 590 cm−1 reaches maximum intensity, while in celadonite, the band at 550 cm−1 is the primary band. The spectra of the samples studied in this work showed both bands: one strong at 586 cm− 1, and the other strong at 548 cm−1. The laser power was controlled because excessive irradiation would lead to broad spectra with one band centred at 585 cm− 1 for both species (Ospitali et al., 2008). The peak that appeared at 700 cm−1 is found in both minerals. The small bands that appeared at 319, 357 and 456 cm−1 can also be attributed to glauconite (Ospitali et al., 2008). However, in several samples studied in this work, the peak at 456 cm−1 presented the maximum intensity. We considered that in this case, the presence of this peak with its high intensity can be attributed to the presence of Egyptian blue or green, which were detected in these samples by XRD and EDX. The small differences in the position and intensity of the peaks in the range between 100 and 300 cm− 1 together with the presence of the two peaks at 586 and 548 cm−1 suggested the presence of a mixture of celadonite and glauconite. The mixture of both minerals, despite their different origin, has also been found by Ospitali et al. (2008) in an archaeological site in Central Italy called Sussa (Ancona) and Pisaurum (Pesaro-Urbino). This technique confirms that in some fragment of the wall paintings studied, a pigment made from celadonite and glauconite was used; in some samples, a mixture with Egyptian blue and a mixture of Egyptian blue and Egyptian green were also present.
Fig. 10. Raman spectra performed on cross-sections of some samples of group ii).
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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3.3. Painting supports Painting supports were shown to vary in terms of the number of layers present and the relative coarseness of the mortars used, which will be referred to herein as “intonaco” (Piovesan et al., 2011). The paint was applied to the topmost of the layers (Rowland, 1999); in this work, we have studied this top layer. Chemical analysis was performed for both crystals (i.e., aggregate) and matrices (i.e., binders). Four classes of intonaco were found in the studied samples. A cross-section of the first group of intonaco is shown in Fig. 2i. The chemical analysis of the aggregates showed the presence of only Ca and small percentages of Si and Al. This aggregate consists of euhedral calcite crystal. The petrographic study showed a micrite-like matrix composed of crypto and microcrystalline calcite. The matrix is composed primarily of Ca with small amounts of Si, Al, K and sometimes Fe (Fig. 11a). These pieces of information confirmed the presence of calcite and silicates. The presence of euhedral calcite crystals also confirmed the presence of intonaco nominated marmorino. The aggregates of the second group (cross section in Fig. 2j) are completely different to the previous group. The chemical analysis showed the presence of Si, which can be attributed to fragments of quartz (Fig. 11b). The matrix showed a similar composition to that of the first group describe in this work. The aggregates of the third group (cross-section in Fig. 2k) showed another composition. The chemical analysis showed fragments with different chemical compositions that can be attributed to dolomite (Fig. 11c), feldspars (Fig. 11d) and quartz. The matrix is similar to those in the other studied samples. The cross-sections of three of the studied fragments showed two painting layers separated by a layer of white colour (cross-section in Fig. 2l). The white colour layer is composed of a calcite with lower porosity. These results confirmed that different aggregates have been used to create the intonaco. 4. Conclusions The green colour palette of the Roman wall paintings found in the Seville Alcazar excavation is consistent with that observed throughout the Roman Empire. Two groups of pigments have been found. The X-ray diffraction study did not allow the differentiation of celadonite and glauconite; however, mica and chlorite were characterised. The punctual chemical analysis performed by SEM–EDX, FTIR and Raman spectroscopy showed the presence of celadonite in the first group (i). The SEM–EDX study characterised particles composed of chromium that were not included
Fig. 11. EDX analysis performed in grains of different supports of the wall-painting.
in the octahedral coordination of the mica. Chlorite has also been detected in all studied samples of this group. The presence of this mineral and chromium oxide is also responsible for the observed green colour. The presence of celadonite and chromium in these pigments suggested that the green earth used in this group of Roman wall paintings was originated from caves near Verona. In the second group (ii) of the studied fragments, inexpensive pigments, such as green earth, mixed with precious pigments, such as Egyptian blue and Egyptian green has been identified. SEM–EDX provided the best characterisation of the mixture of Egyptian blue and Egyptian green; however, overlapping of the peaks of these two pigments in the XRD diagrams has hindered characterisation using this technique. Micro-Raman spectroscopy was the only technique that was able to distinguish the mixture of celadonite and glauconite present in the fragments of the second group. The presence of Sn in the two samples indicated that Cu was derived from bronze while the absence of this element most likely suggested a different origin of the Cu used, which may have been ore deposits. For the preparation layers, three different types of intonaco have been recognised based on the composition of their aggregate. The matrix is composed primarily of Ca with small amounts of Si, Al and sometimes K and Fe. White layer composed of calcite with lower porosity has been also found between two painting layers. All data and, in particular, the absence of trace amounts of organic binders and a carbonation layer suggested that the most utilised painting technique was fresco. In two samples, two layered coloured samples were found. The carbonation layer between the two differently coloured layers suggested that the superficial painting one was applied with a lime painting technique. Acknowledgements The authors are indebted to the Patronato de los Reales Alcazares de Sevilla for their collaboration with this investigation. The financial support of the CHARISMA — FP7 n. 228330, the Spanish Commission Interministerial de Ciencia y Tecnología (CICYT) under project BIA200912618 and the Junta de Andalucia (TEP-6558) is also acknowledged. Samples were provided by M.D. Robador, architect, and M.A. Tabales and A. Duran, archaeologists. References Aliatis, I., Bersani, D., Campani, E., Casoli, A., Lottici, P.P., Mantovan, S., Marino, I.-G., Ospitali, F., 2009. Green pigments of the Pompeian artista` palette. Spectrochim. Acta A Mol. Biomol. Spectrosc. 73, 532–538. Augusti, S.I., 1967. Colori Pompeiani. D Luca Editore, Rome. Bianchetti, P., Talarico, F., Vigliano, M.G., Ali, M.F., 2000. Production and characterization of Egyptian blue and Egyptian green frit. J. Cult. Herit. 1, 179–188. Brindley, G.W., Brown, G., 1980. Crystal Structures of Clay Minerals and Their X-ray Identification. Mineralogical Society, London. Canti, M.E., Heathcote, J.L., 2002. Microscopic Egyptian blue (synthetic cuprorivaite) from sediment at two archaeological sites in West Central England. J. Archaeol. Sci. 29, 831–836. Castellato, U., Vigato, P.A., Russo, U., Matteini, M., 2000. A Mösbauer approach to the physic-chemical characterization of iron containing pigments for historical wall paintings. J. Cult. Herit. 1, 217–232. Clementi, C., Ciocan, V., Vagnini, M., Doherty, B., Tabasso, M.L., Cunti, C., Brunetti, B.G., Miliani, C., 2011. Non-invasive and microdestructive investigation of the Domus Aurea wall painting decoration. Anal. Bioanal. Chem. 401, 1815–1826. Domenech-Carbo, M.T., Bosh-Reig, F., Gimeno Adelantado, J.V., Periz-Martinez, V., 1996. Fourier transform infrared spectroscopy and the analytical study of works of art for purposes of diagnosis and conservation. Anal. Chim. Acta 330, 207–215. Drits, V.A., Dainyak, L.G., Muller, A., 1997. Isomorphous cation distribution in celadonites, glauconites and Fe-illites determined by infrared, Mössbauer and EXAFS spectroscopies. Clay Miner. 32, 153–179. Duran, A., Jimenez de Haro, M.C., Perez-Rodriguez, J.L., Franquelo, M.L., Herrera, L.K., Justo, A., 2010. Determination of pigments and binder in Pompeian wall paintings using synchrotron radiation-high-resolution X-ray powder diffraction and conventional spectroscopy–chromatography. Archeometry 52, 286–307. Duran, A., Perez-Rodriguez, J.L., Jimenez de Haro, M.C., Franquelo, M.L., Robador, M.D., 2011. 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. J. Archaeol. Sci. 38, 2366–2377.
Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016
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Please cite this article as: Perez-Rodriguez, J.L., et al., Green pigments of Roman mural paintings from Seville Alcazar, Appl. Clay Sci. (2015), http:// dx.doi.org/10.1016/j.clay.2015.03.016