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Journal of Archaeological Science 41 (2014) 541e555

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Journal of Archaeological Science

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Identification of pigments on Byzantine wall paintings from Crete(14th century AD) using non-invasive Fiber Optics Diffuse ReflectanceSpectroscopy (FORS)

Eleni Cheilakou a,*, Michail Troullinos b,1, Maria Koui a

aChemical Engineering School, Materials Science and Engineering Section, NDT Lab, National Technical University of Athens, 9, Iroon Polytechniou Str.,15870 Zografou, Athens, Greeceb 28th Ephorate of Byzantine Antiquities, Conservation Department, 214, Arkadiou Str., 74100 Rethymno, Crete, Greece

a r t i c l e i n f o

Article history:Received 15 May 2013Received in revised form22 September 2013Accepted 23 September 2013

Keywords:Non-invasive techniquesFORSESEM-EDXATR-FTIRMicro-RamanIdentification of paintings’ pigmentsCretan Byzantine wall paintings

* Corresponding author. Tel.: þ30 210 7723233, þ3E-mail addresses: elenheil@mail.ntua.gr (E

chemeng.ntua.gr (M. Troullinos), 28eba@culture.gr (M1 Tel.: þ30 28310 23653.

0305-4403/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jas.2013.09.020

a b s t r a c t

In this paper a combined analytical methodology was employed aiming to explore the potential of thenon-invasive Fiber Optics Diffuse Reflectance Spectroscopy (FORS) technique for Byzantine wall paintingpigments’ characterization, as well as to assess the reliability of analytical information comparing theresults with detailed spectral analyses obtained by advanced laboratory techniques such as Environ-mental Scanning Electron Microscopy with Energy Dispersive X-Ray Analysis (ESEM-EDX), AttenuatedTotal Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and micro-Raman Spectroscopy.Byzantine wall paintings (14th Century) decorating two Churches located in the settlements of Patsosand Meronas at Amari, Crete, were investigated in a first systematic research effort to study the muralpainting pigments and techniques employed on the island during this period. Micro-sampling wasallowed for laboratory analyses only from the Patsos Church’s murals. The results obtained from thevarious spectroscopic methods employed confirmed the identification of pigments (red/yellow ochres,cinnabar, green earth, etc) and that the mixed fresco-secco technique was used in these paintings. Inorder to characterize the Meronas murals, a comparative study was performed between the acquiredFORS spectra of both Churches and the laboratory analyses results. The data obtained confirmed theeffectiveness of FORS technique for wall painting pigments’ identification, offering key advantages suchas instrument mobility and rapid data collection which are of utmost significance in the field ofarchaeological research.

The present work provides detailed information on the structure of pigments and the interpretation ofthe FTIR spectra by assigning characteristic vibrational modes in these spectra and the electronic tran-sitions of the VIS-NIR spectra, which would be of great value as a reference for other FTIR and FORSresearchers in this field.

� 2013 Elsevier Ltd. All rights reserved.

Pigments’ identification on archaeological artifacts such as wallpaintings is crucial for the deep understanding of the rawmaterialsand the painting techniques applied (Thompson, 1998), as well asfor protection purposes as it could contribute significantly towardsthe selection and employment of the most appropriateconservation-restoration procedures. In order to characterize thepalette used by the original artist and to yield information useful toscientists and conservators, several analytical methods are avail-able (Bikiaris et al., 1999; Daniilia et al., 2000; Pavlidou et al., 2006;

0 210 7723214.. Cheilakou), markoue@. Koui).

All rights reserved.

Daniilia et al., 2008; Hein et al., 2009; Iordanidis et al., 2011).Considering that there are strict regulations where sampling forchemical analysis is restricted or even prohibited, there is an urgentneed to develop non-invasive methodologies where more versatile,robust and simpler techniques should be employed, which arecapable of performing on-site analytical studies rapidly withoutincurring any damage on the under investigation wall painting, aswell.

Among the portable techniques, the XRF, Raman and micro-Raman have been employed extensively in the study of murals(Appolonia et al., 2009; Perardi et al., 2003). Nevertheless, XRF issometimes not conclusive, since it is an elemental analysis method,yielding therefore an indirect identification of pigments throughevidence of key-chemical elements. Raman spectroscopy has high

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555542

diagnostic power, however it is difficult when used in-situ and re-quires lengthy times of analysis. A good alternative to thesepowerful but sophisticated techniques is Diffuse ReflectanceSpectroscopy with fiber optics (FORS). This technique allows rapiddata acquisition that enables quick surveying of the wall paintingsproviding pigments’ characterization in an effective manner.Moreover, it is suitable for operating in all geometrical situations orsome non-easily accessible areas (i.e. high scaffoldings) and thanksto its versatility, it has amajor advantagewhen dealing with on-siteinvestigations. The major drawback of FORS is that it does notprovide information on the stratigraphy, when layering of pigmentsare investigated, as well as when organic binders are present.Spectroscopic imaging techniques (such as infrared, ultraviolet, etc)together with luminescence spectroscopy, which could be used andalso coupled with FORS on the stratigraphy of pigments. As far asmixtures of pigments are concerned, the FORS technique could beimproved (Cheilakou et al., 2009). FORS analyses have been carriedout on several paintings (Bacci, 1995, 2006; Dupuis et al., 2002).However, the application of this tool in the field of mural investi-gation is restricted and mainly concentrated on frescoes of theMiddle Ages and Renaissance, as reported lately (Picollo et al.,2000).

The present study is aiming at the analytical characterization ofByzantine wall paintings (14th Century) from Rethymno, Crete,located in the southern part of the Aegean Sea. While a vastamount of research works have been published concerning pig-ments identification on Byzantine wall paintings of various origins(Bikiaris et al., 1999; Daniilia et al., 2000; Pavlidou et al., 2006;Daniilia et al., 2008; Hein et al., 2009; Iordanidis et al., 2011),the existing analytical information regarding Byzantine muralsfrom Crete is scarce (Westlake et al., 2012). Therefore, this paper isindeed the first systematic research attempt to study an adequateseries of pigments, the results of which are expected to providesubstantial information on the level of the adopted wall paintingmaterials and techniques in Byzantine Crete, as well as to helpscientists and conservators, who are working in this area in orderto decide upon the most compatible conservationerestorationprocedures.

The wall paintings decorate the Churches of Panagia andTheotokos built in the settlements of Patsos and Meronas at Amari,respectively. Due to their great historical and artistic value, micro-sampling was permitted only from the Patsos wall paintings, sub-sequently settling the need for a strictly non-invasive examinationof the murals in Meronas. Therefore, a combined analytical meth-odology was employed involving (a) non-invasive portable VIS-NIRFORS for the performance of in-situ measurements on bothChurches’ wall paintings, and (b) ESEM-EDX, ATR-FTIR and micro-Raman that served as reference laboratory methods providingdetailed compositional and molecular information of the samples’pigments. In order to identify the pigments fromMeronas murals, acomparative study was carried out between the FORS spectra ofboth Churches and the laboratory analyses results. Pigment iden-tification was also derived from comparing the collected diffusereflectance spectra with suitable spectral databases provided byliterature. The interpretation of the FORS spectra is discussed indetail. The main objective of this study was to explore the potentialof VIS-NIR FORS for pigments’ characterization, as well as to assessthe reliability of analytical information comparing the results in thecombined analytical methodology.

1. Description of the wall paintings e historical data

A flourishing of Byzantine art occurred in Crete from the 13th tothe 17th Centuries, the period of the Venetian occupation of theisland. The Italian archaeologist Gerola (Gerola, 1905) listed more

than 800 wallpainted churches in Crete, the majority decoratedbetween 1225 and 1523. Hundreds of them have survived today,scattered throughout the island and constituting an invaluablereligious, cultural and artistic value. In the province of Rethymno,more than 150 remarkable Byzantine monuments are preservedwith murals of inestimable artistic value (Kalokyris, 1973).

The wall painting of the Panagia Church at Patsos is dated backto the first decade of the 14th century and has been associated withspecific historical events, such as the actions of the Cretan rulerAlexios Kallergis in the wider region of Milopotamos after theenforcement of the 1295 Treaty with the Venetians. The murals areof particular interest for tracking the penetration of Palaiological artin Crete, in an era where the average artistic level was not high inthe island due to its isolation. The wall painting was extendedalmost to the entire Temple. The lower part of the wall depictsfrontal standing Saints, focusing on hierarchs, while the upper partportrayed scenes focusing on the life of Virgin Mary. On the sidewalls of the Sanctuary there were two scenes such as the society ofApostles and the Ascension of Christ. The scenes and the individualshapes are depicted with monumental dimensions and specialcharacteristics such as the heavy volumes, rich in drapery clothingwith brightly lit of the points projecting, the use of complementarycolors to the presentation of the faces and with an intense mobility.The Patsos Church’s frescoes are completely different from thepoint of view of art level practiced during this period in Crete, andthey are categorized into the realistic tendencies of Palaiologicalpaintings that evolve by the end of 13th century (Andrianakis,2002).

Since 1903 the above monument has been in ruins afterdestruction by earthquake. In general the roof of the temple is notpreserved, just some parts of its walls and fragments of wall dec-orations still exist, which are not kept in very good condition due tothe bad preservation of the building. A large part of the walldecoration was detached and moved to Heraklion for protectionpurposes in 1973, where since then is exhibited in the collection ofAgia Aikaterini Church. Some detached fragments are also saved inthe Conservation Department of Rethymno (Andrianakis, 2002).

The Church of Theotokos in Meronas is a domed three-aisledBasilica attributed to Virgin Mary, Saint George and Apostles Pe-ter and Paul. The interiors of the central and northern aisles aredecorated with wall paintings dated back to the second half of 14thCentury, displaying numerous shapes of Saints, Hierarchs andscenes of the Christological and Evangelic cycles that impress withtheir high esthetic levels. The murals of Meronas is a high qualitywork of art and strongly reflects the conservative and academictrends evolving in Constantinople, whose appearance in Creteduring this period is associated with the activities of the renownedKallergis family. The coat-of-arms of Kallergis family depicted inwall decorations affirm the direct contribution of this illustrioushouse of the Cretan nobility to the penetration and disseminationof the idealistic and conservative stylistic trend in the fiefs he heldin western and central Crete. Paramount monument of this trend isthe Theotokos Church in Meronas (Borboudakis., 1986).

2. Experimental

2.1. Micro-sampling

Totally 13 micro-samples (S1eS13) were collected from selectedwall painting fragments saved in the Panagia Church at Patsos(Fig. 1c), as well as from detached fragments that are today dis-played in the Conservation Department of Rethymno (Fig. 1a, b),which were representative in order to cover the majority of colorsappearing within the two Churches. In-situ FORS measurementswere performed at multiple spots of almost all color impressions

Fig. 1. Wall paintings originating from the Panagia Church at Patsos, Amari, representing: (a) Agia Fotini and (b) Agios Nikolaos saved in the Conservation Department of Rethymno,(c) remains of Military Saints saved in the southern wall of the Church at Patsos.

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555 543

appearing in the above fragments (Fig. 1aec, see labeled spots a, b, c,etc), as well as in selected wall paintings decorating the TheotokosChurch at Meronas (Fig. 2aec, see dotted arrows).

2.2. Methods of analysis

2.2.1. Laboratory analytical procedures2.2.1.1. ESEM-EDX. All samples were initially examined under a FEIQuanta 200 Environmental Scanning Electron Microscope (ESEM),coupled with an Energy Dispersive X-Ray Detector (EDX), for themicrostructure investigation and the chemical elemental analysisof the pigments. ESEM imaging parameter were selected as follows:30 kV accelerating voltage, magnifications up to �400 and dwelltime of 5 ms for each single image. The surface elemental compo-sition was determined by EDX detector using: spot analysis locallyat different selected spots of interest, and surface analysis (map-ping) on the whole image. The Quanta 200 ESEM system can

provide high resolution images without requiring any samplingpretreatment (carbon or gold coating), thus enabling to leave thesamples intact for further analysis.

2.2.1.2. ATR-FTIR. For the characterization of the pigments’ mo-lecular structure, all samples were analyzed using a Thermo-Scientific Nicolet 6700 Fourier Transform Infrared Spectrometer(FTIR), equipped with an Attenuated Total Reflectance (ATR)accessory. Transmission FTIR spectra were recorded in the mid-IRspectral region 4000e400 cm�1, at a resolution of 4 cm�1 and bycollecting 120 co-added scans for each spectrum. The approxi-mate collection time was about 1 min. Data processing was car-ried out using the OMNIC 7.1 Software. The great advantage of theATR technique utilized is that minimum amount of sample isrequired without involving any preparation (i.e. KBr pelletiza-tion), enabling, thus to obtain high quality IR spectra of thesamples very quickly.

Fig. 2. Wall paintings from the Theotokos Church at Meronas, Amari, decorating: (a) the wall between the south-eastern and north-western arches representing the coat-of-arms ofthe Kallergis family, (b, c) the Sanctuary representing the Melismos (in Greek Mεlismó2) and the Presentation of the Virgin, respectively.

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555544

2.2.1.3. Micro-Raman. micro-Raman spectroscopy was used as anadditional technique, in order to shed light on uncertain cases,regarding the molecular structure of pigments and to confirmprevious identifications of pigments. A JY T64000 triple mono-chromator system in subtractive mode was employed that operateswith three 1800 lines/mm holographic gratings and is equippedwith an OLYMPUS BH2-UMA optical microscope of magnificationup to 100�, a liquid nitrogen CCD detector and motorized steppingdrive motors for the scanning of the samples. An Arþ ion laser beamserved as the excitation source operating at the wavelengths of514.5 nm and 488 nm. Low laser excitation beam power up to 1mWwas used for obtaining spectra acquisition in the region between100 and 1700 cm�1, with a collection time of 4e6 h and an accu-mulation spectra of 5e14 scans/spectrum.

2.2.2. In-situ investigation procedures2.2.2.1. Fiber Optics Diffuse Reflectance Spectroscopy (FORS).In-situ measurements were performed using a portable OceanOptics, USB4000-VIS-NIR Fiber Optic Reflectance Spectrometer(FORS) that features a high-performance 3648-element linear CCD-array detector, installed with a multi-bandpass order-sorting filterto cover the 350e1000 nmwavelength range, and a 25 mmentranceslit for optical resolution to 1.5 nm. The instrument is equippedwith a QR400-7-VIS/NIR reflection bifurcated probe providing

illumination and detection of diffused light from the same direc-tion, an HL-2000 tungsten-halogen light source and a probe holderpositioning the QR400-7 at 45� for diffuse reflection in order not toinclude specular reflectance. Use of this device allows also one toassure a constant distance between the probe and the surface to beanalyzed, in the same time avoiding external light contributions.Diffuse reflectance spectra were referenced against WS-1 Standardand guaranteed reflective at 98% or more in the spectral rangeinvestigated. The spectra were taken instantaneously. Data treat-ment was performed with the SpectraSuite software add-on forExcel.

3. Results and discussion

3.1. Laboratory results

The ESEM-EDX, ATR-FTIR and micro-Raman analysis of themicro-samples led to the following results regarding the identifi-cation of pigments, organic binders and the painting technique ofthe Panagia Church’s wall paintings at Patsos, Amari.

3.1.1. The wall painting techniqueThe EDX chemical elemental analysis results revealed the

presence of high Ca content as major component of almost all the

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555 545

examined samples (Table 1), suggesting the presence of calciumcompounds. Indeed calcium carbonate was identified by the strongcharacteristic signature bands of CaCO3 recorded in all samples byATR-FTIR bands near 1410, 870 and 710 cm�1 (Figs. 3a, 4a and 7)indicating that CaCO3 was in the form of calcite (see Table 2). Thecombination mode n1 þ n4 (1085 þ 710) was also observed at1795 cm�1. The n1CO3

¼ stretching vibration gives rise to a verystrong Raman band near 1085 cm�1, which is normally inactive inIR (Theophanides and Anastasopoulou, 2010; Farmer, 1974).

Furthermore, the presence of organic matter was identified inalmost all ATR-FTIR spectra by the weak absorption bands in theregions of 2920, 2850 cm�1 and 2960, 2870 cm�1 attributed to theasymmetric and symmetric stretchings for methylene and methylgroups, respectively, of phospholipids. The band appearing near1730 cm�1 is evidence for the presence of ester carbonyl groups(nC]O carbonyl stretching), and the bands near 1160 and1240 cm�1 are spectral features attributed to cholesterol estergroups involved in oxidized molecules of cholesterol. The lattercould also be assigned to vibrations of PO2

- groups of phospholipidsand/or DNA. In addition, all spectra showed a broad carbonyl ab-sorption band near 1650 cm�1, called Amide I, which is represen-tative of eNHeCOe vibrations of the peptide group of proteins,arising mainly from C]O stretching vibrations with minor contri-butions from the in-plane dNeH bending. All the above mentionedspectral features are consistent with the presence of egg as anorganic binder (Theophanides et al., 1988; Derrick et al., 1999;Meilunas et al., 1990; Mamarelis et al., 2010). Fresh egg showstwo characteristic bands, one at 3006 cm�1 attributed to unsatu-rated ]CH stretching vibrations and another single ester carbonylband at 1746 cm�1. In aged eggs the first band shifts to 3080 cm�1

and the second band splits into two bands near 1714 and 1730 cm�1

(Meilunas et al., 1990), where in our case only the latter(1730 cm�1) is shown due to the presence of other constituents andto the fact that our spectra are tooweak in this region. In the higherspectral range between 3140 and 3500 cm�1 the primary amidesshow two bands arising from the vasNeH and vsNeH stretchingvibrations, which are not distinct in the obtained ATR-FTIR spectrabut appear in the form of a very broad band due to hydrogenbonding of the NeH groups (Theophanides et al., 1988; Derricket al., 1999; Meilunas et al., 1990; Mamarelis et al., 2010).

The presence of calcite confirms that the fresco technique wasinitially employed by the Byzantine artist, which involves themixing of pigments with water or lime water followed by theirapplication on damp lime-based plaster. As the plaster dries, thepigment is pulled into the surface of the plaster and stabilized by

Table 1EDX elemental analysis of samples with red (S1eS4), brown (S5eS7), black (S8, S9), yellowPanagia Church at Patsos, Amari (Wt%).a

El. S1/Deepred

S2/Brightred

S3/Orange-red S4/Ceramic-red S5/Darkpurple-brown

SB

map map spot map spot map spot map spot m

C 34.5 31.9 17.5 14.3 15.7 11.2 8.4 51.5 25.3 3O 31.9 32.8 21.8 43.8 43.6 45.1 42.1 27.3 32.1 3Mg 2.6 1.9 1.6 3.4 0.8 2.4 1.1 0.7 0.9 0Al 1.3 0.7 1.1 1.4 0.9 2.8 1.2 0.4 0.8 1Si 8.4 4.4 2.9 6.3 3.8 11.3 5.1 2.1 2.8 4K 0.44 0.4 0.2 0.6 0.5 0.7 0.2 0.3 0.4 0S 0.6 2.6 6.6 0.5 3.4 0.6 0.2 0.8 0.9 1Ca 15.3 17.9 5.9 23.4 12.2 21.3 6.4 9.9 7.8 1Fe 3.2 1.6 1.3 4.3 17.3 3.6 34.5 6.3 27.4 1Hg 1.6 5.1 40.0 n.d. n.d. n.d. n.d. n.d n.d. nCl n.d. n.d. 0.3 0.3 0.3 0.4 0.3 0.2 0.3 nNa n.d. n.d. 0.8 0.8 0.9 n.d. n.d. n.d. 0.4 nTot 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 1

a The numbers are rounded to the tenth maximum/minimum; n.d.: not-detected.

Ca(OH)2 that reacts with CO2 and slowly is converting into CaCO3.The protein-containing organic matter identified by ATR-FTIRshows that secco was also applied after the plaster was dried(over the fresco), probably to add details or make alterations, usingpigments mixed with egg as an organic binding medium(Thompson, 1998; Taft and Mayer, 2000).

3.1.2. Red pigmentsThe EDX results of the red samples (S1, S2, S3, S4) reported in

Table 1, revealed the presence of considerable Si and lower Alconcentrations indicating the existence of aluminosilicate com-pounds. The determination of Fe contents which seem to beremarkably increased in samples S3 (orangeered) and S4(ceramicered) suggest the presence of iron oxide [Fe2O3] as themain component of the pigment producing the red color. Moreover,the coexistence of aluminosilicates possibly in the form of kaolinite[Al2Si2O5(OH)4)], leads to the consideration that the pigment usedwas red ochre. Samples S1 (deep red) and S2 (bright red), present adifference referring to the use of not only red ochre but also cin-nabar. Cinnabar identification is based on the detection of Hg and Samounts, which were particularly high in sample S2 comparedwith sample S1, and also with respect to its lower Fe content. Theaforementioned results suggest that the red color of samples S1 andS2 come from a mixture of red ochre and cinnabar in differentproportions, with the higher HgS content to exist in the bright redcolor impressions.

The above hypothesis concerning red ochre is confirmed by theATR-FTIR spectral analysis of the red samples. The spectra obtained(Fig. 3a, Table 2) showed intense absorption bands near 1005 and1030 cm�1 that could be attributed to the in-plane stretching vi-brations of the equatorial SieO bonds of kaolinite associated withtetrahedral polyhedra (Farmer, 1974; Madejová, 2003). This is dueto the stresses imparted by the octahedral sheet in kaolinite, whichare transferred to the Si4þ tetrahedral sheet resulting in a distortionof its structure and a reduction of the degeneracy of the SieOmodes (Schroeder, 2002). Therefore, the well-defined SieO ab-sorption band produced by the silicate minerals between 1000 and1200 cm�1 due to their fully ordered crystalline lattice structure, inthe case of layer silicates as kaolinites splits into two or more peaks,since some of the double bond of Si]O bonds are held perpen-dicular to the layers, while others vibrate in-plane with the layers(Derrick et al., 1999).

In the higher spectral region 3400e3700 cm�1, the spectrashowed weak absorption bands near 3620 cm�1 assigned tostretching of the inner OH-groups of kaolinite lying between the

(S10) and green (S11eS13) color impressions collected from thewall paintings of the

6/rown

S7/Darkpurple-brown

S8/Black S9/Bluish-black

S10/Yellow

S11/Green

S12/Darkgreen

S13/Green

ap map map spot map map map map

4.8 7.4 29.4 52.7 33.3 10.3 9.9 19.95.7 39.8 37.2 25.5 32.0 50.6 52.0 40.5.9 1.8 1.8 1.0 2.0 2.0 2.4 2.2.0 1.5 0.7 0.3 0.7 0.7 0.4 0.9.2 4.5 3.8 2.2 5.6 5.3 2.4 7.8.2 3.6 0.2 0.4 1.2 1.2 0.6 1.7.6 6.0 0.6 0.6 0.8 4.0 7.1 0.30.3 18.3 24.4 16.6 20.7 21.8 22.2 23.61.3 11.8 0.6 0.3 2.2 2.3 1.3 2.8.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d..d. 0.6 0.6 0.3 0.7 0.6 0.7 n.d..d. 1.2 0.5 n.d. 0.7 1.0 1.0 0.400.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Fig. 3. (a) ATR-FTIR absorption spectrum and (b) micro-Raman spectrum of red samples S1 (deep red) and S2 (bright red), respectively.

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555546

tetrahedral and octahedral sheets, and in the regions of 3690 and3650 cm�1 attributed to the in-plane and out-of-plane stretchingvibrations of the inner-surface OH-groups, respectively. These OH-groups reside in the octahedral surface of the layers and formweakhydrogen bonds with the oxygen of the SieOeSi bonds on thelower surface of the next layer. The band near 910 cm�1 could beassigned to the inner hydroxyl bending vibrations (dAleOH) ofkaolinite (Farmer, 1974; Madejová, 2003; Schroeder, 2002; Frostet al., 1993). Normally, low amounts of quartz [SiO2] are foundwithin kaolinite, which are identified by the characteristic doubletpeak appeared at 795, 780 cm�1 and the bands near 1083 and690 cm�1 arising by the symmetrical and asymmetrical stretchingand bending vibrations of the SieO group, respectively (Farmer,1974; Derrick et al., 1999; Ramasamy and Suresh, 2009; Hlavayet al., 1978; Fernández-Carrasco et al., 2012). Finally, in the lowerspectral region the bands near 530 and 460 cm�1 could be attrib-uted to dSieO bending vibrations and terminal groups nAleO ofkaolinite (Schroeder, 2002; Bougeard et al., 2000).

Samples S1 and S2 were further analyzed with micro-Ramanspectroscopy in order to identify cinnabar, whose characteristicbands appear at a spectral range lower than 400 cm�1 and is

impossible to reveal with the ATR-FTIR instrument using a detectorwhich absorbs in this region. The obtained micro-Raman spectra(Fig. 3b) recorded a band at 253 cm�1 and a poorly-resolved band at344 cm�1, attributed to the n(HgeS) stretching vibration of cinna-bar (Daniilia et al., 2000; Edwards and Chalmers, 2005).

3.1.3. Brown and black pigmentsThe EDX elemental results of the brown samples (S5, S6, S7)

summarized in Table 1, identified high Fe levels along with lower Siand Al concentrations, suggesting the existence of hematite [Fe2O3]as the main component of the pigment. Since no Mn was detected,the possible use of raw or burnt umber whose brown hue arisesfrom the MnO2 was excluded. Moreover, considerable S amountswere determined in samples S6 and S7 collected from the Churchthat could be associated with the organic medium used for thepreparation of the pigments, as well as with the paintings’ surfacescolonized by microorganisms.

Typical bands for aluminosilicate compounds were recorded inthe ATR-FTIR spectra of the brown samples (Fig. 4a, Table 2) con-firming the presence of ochre. The spectra of samples S6 and S7showed also strong absorption bands near 669 and 599 cm�1,

Table 2Materials identified with ATR-FTIR and micro-Raman spectroscopy in samples collected from the wall paintings of the Panagia Church at Patsos, Amari

Sample/Colorimpression

ATR-FTIR absorption bands (cm�1) Micro-Ramanbands (cm�1)

Pigment

Calcite Kaolinite Quartz Celadonite Organic binder

S1/Deep red n3asymCO3¼ stretching 1410

n2asymCO3¼ out-of-plane

bending 870n4symCO3

¼ in-planebending 710n1 þ n4 1795n1 ¼ 1085, from Ramann1 ¼ 1795e710

nOH 3620,3690, 3650dOH 910nSieOeSi(Al)1005,1030dSieOeSi, AleO530,460

nSieOeSi795, 780nSieOeSi1083dSieOeSi693

nCH2 2920, 2850vCH3 2960nC]O 1730 (ester)nC]O 1650 (protein)

Cinnabarn(HgeS) 253,344

Mixture of Cinnabar[HgS] and red ochreS2/Bright red

S3/Orange-red Red ochre Hematite[Fe2O3]S4/Ceramic-red

S5/Darkpurple-brown

n3asymCO3¼ stretching 1405

n2asymCO3¼ out-of-plane

bending 870n4symCO3

¼ in-planebending 710n1 þ n4 1795n1 ¼ 1085, from Ramann1 ¼ 1795e710

nOH 3690dOH 910nSieOeSi(Al) 1030dSieOeSi, AleO530,460

nSieOeSi795, 780nSieOeSi1083

nCH2 2920, 2850nC]O 1736 (ester)nC]O 1646 (protein)

Hematite [Fe2O3]probably mixed withcalcite or carbon black

S6/Brown dOH 910nSieOapicaleSi 1110nSieOeSi(Al)1005,1030SieOeAl 786, 756dSieOeSi, AleO530,460

S7/Darkpurple-brown

nCH2 2920, 2850vCH3 2960, 2870nC]O 1736 (ester)nC]O 1646 (protein)

HematitedFeeO 245, 294,410, 616nFeeO 225, 503

S10/Yellow n3asymCO3¼ stretching 1402

n2asymCO3¼ out-of-plane

bending 871n4symCO3

¼ in-planebending 710n1 þ n4 1793, n1¼ 1083from Ramann1 ¼ 1793e710

nOH 3691dOH 910nSieOeSi(Al)1012,1080dSieOeSi, AleO533, 432

nCH2 2921, 2852vCH3 2959, 2874nC]O 1729 (ester)nC]O 1649 (protein)

GoethitenFeeOeFe/eOH 390dFeeO 299

Yellow ochre-Goethite[FeO(OH)]

S11/Green n3asymCO3¼ stretching 1410

n2asymCO3¼ out-of-plane

bending 870n4symCO3

¼ in-planebending 710n1 þ n4 1795n1 ¼ 1085, from Ramann1 ¼ 1795e710

nOH 3530, 3555dOH 800nSieOeSi 959,972, 1075, 1108SieOeFe(Al),Fe(Al)eOH440,458, 488

Green earth-Celadonite[K[(Al,Fe3þ), (Fe2þ,Mg)](AlSi3,Si4)O10](OH)2]

S12/Dark green nCH2 2924, 2850vCH3 2960nC]O 1732 (ester)nC]O 1650 (protein)

S13/Green nOH 3529,3554, 3598dOH 798nSieOeAl 1012nSieOeSi 972,1078,1109SieOeFe(Al),Fe(Al)eOH438,461

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555 547

which could be attributed to the vibrations of the nCeS and nSeSgroups, indicating the presence of sulfones on the initially utilizedorganic material likely associated with egg, thus confirming thehigh S levels detected by the EDX results (Table 2). The eOHstretching and bending vibrations of the adsorbed water occur near3400 and 1620 cm�1, respectively. The latter could also be assignedto nOeNO2

� stretching of nitrate groups or amide I (Theophanidesand Anastasopoulou, 2010; Anastassopoulou et al., 1997). The bandappearing near 3530 cm�1 could be attributed to vibrations of OH-groups produced by the hyperoxidation of lipids and proteins(Mamarelis et al., 2010). Finally, the band observed at 1323 cm�1

could arise from the nsCeO vibrations of COO� groups, suggestingthe possible presence of calcium oxalate metalcomplex[CaC2O4$nH2O] as a degradation product (Pavlidou et al., 2006;Aliatis et al., 2009).

The presence of hematite was identified in the micro-Ramanspectrum of sample S7 (Fig. 4b) by the bands at 245, 294, 410,616 cm�1 arising from the FeeO Eg symmetric bending vibrations,and the bands at 225, 503 cm�1 assigned to the FeeO A1g sym-metric stretching vibrations (Legodi & deWaal, 2007; Bouchard andSmith., 2003). The band observed near 660 cm�1 could be assignedto the FeeO A1g symmetric stretching mode of magnetite [Fe3O4]

that is suggested to exist in the Raman spectra of hematite becauseof partial transformation into magnetite under the laser beam(Legodi & deWaal, 2007). All the aforementioned results lead to theconclusion that the brown colorations come from red ochre withhigh content of hematite, probably mixed with either calcite tolighten the color tone or with carbon black to darken the tone.Vegetable carbon was identified from the micro-Raman analysis ofthe black samples (S8, S9) by the doublet band recorded around1370 and 1600 cm�1 (Fig. 5) that can be assigned to the n(CeC)stretching vibrations of amorphous carbon, corresponding to thesp3 kai sp2 forms of hybridized carbon, respectively, the so-called Dband (CeC bonding, diamond A1g mode) and G band (C]C bonding,graphite Eg mode) (Silva, 2003). A calcined bone or ivory source forthis carbonwas excluded since neither phosphorus was detected inthe black pigment by the EDX results (Table 1), nor any signaturephosphate bands at 960 cm�1 were identified in the Raman analysis(Edwards and Chalmers, 2005).

3.1.4. Yellow pigmentsThe considerable Si content determined in the yellow sample

(S10) by the EDX results (Table 1) along with the lower Fe and Alconcentrations indicate the presence of yellow ochre, possibly in

Fig. 4. (a) ATR-FTIR absorption spectra of brown samples S5, S7 (dark purpleebrown) and (b) micro-Raman spectrum of sample S7 after smoothing and baseline correction.

Fig. 5. micro-Raman spectrum of sample S9 (bluish-black) after smoothing andbaseline correction.

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555548

the form of goethite, [FeO(OH)] or limonite, [FeO(OH)$H2O]. Theabsence of As or Pb excludes the possible utilization of arsenic- orlead-based yellow pigments such as orpiment [As2S3] or massicot[PbO]. Typical bands for aluminosilicate compounds were recordedin the ATR-FTIR spectrum of the yellow sample (Table 2), while thehydrated iron oxide was identified in the obtained micro-Ramanspectrum (Fig. 6) by the bands appearing at 390 and 299 cm�1,assigned to the symmetrical nFeeOeFe/FeeOH stretching and dFeeO bending vibration of goethite, respectively (Edwards andChalmers, 2005; Legodi & de Waal, 2007; Bouchard and Smith.,2003). The bands occurring at 154 and 282 cm�1 could be attrib-uted to the external modes of bending vibrations of the CO3

¼ ion ofcrystal calcite (Gunasekaran et al., 2006). The above results confirmthe utilization of yellow ochre (goethite) for the production of theyellow colorations.

3.1.5. Green pigmentsThe EDX analysis results reported in Table 1 indicated the

presence of Fe, Si, Mg, Al and K as major components of all theexamined green samples (S11, S12, S13) allowing us to assume thatthe green pigment used was Green Earth. Since no Cu was detected,

Fig. 6. micro-Raman spectrum of sample S3 (yellow).

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555 549

the possible presence of copper-based green pigments such asmalachite [CuCO3$Cu(OH)2] was excluded. Green earths were thecommonest pigments in Byzantine fresco, mainly constituted byceladonite and glauconite, which are both layer silicates of thedioctahedral mica group.

The presence of celadonite [K[(Al,Fe3þ),(Fe2þ,Mg)](AlSi3,Si4)O10](OH)2] is evident in the obtained ATR-FTIR spectra of the greensamples S11, S12 (Fig. 7a) by the presence of bands appearing near955, 970, 1075 cm�1 assigned to the in-plane SieO stretchingmodes, and the band near 1110 cm�1 arising from the SieOstretching vibrations perpendicular to the SiO4 tetrahedral sheet,suggesting quite crystalline order. In the same spectral region 950e1110 cm�1, the ATR-FTIR spectrum of sample S13 (Fig. 7b) isdifferentiated with regard to the aforementioned spectra. Specif-ically, the fine structure in the SieO band characteristic of cela-donite is not distinct, due to overlapping with the intense SieOeAlabsorption band centered at 1012 cm�1 leaving weak shoulders at1078 and 1109 cm�1. This could be attributed to a decreasing ofsymmetry (more disordered structure) in the tetrahedral silicatelayers, taking into account that the shape of the principal SieObands is particularly sensitive to even small differences of Al3þ-for-Si4þ substitutions in the SiO4 tetrahedra, resulting in larger diver-gence from the optimum R3þ:R2þ (where R3þ and R2þ are Fe3þ andFe2þ) ratio of 1:1 in the octahedral layer (Aliatis et al., 2009;Newman, 1979; Ospitali et al., 2008; Moretto et al., 2011).

In the higher spectral region the weak absorption bandsobserved near 3530, 3555 and 3600 cm�1 could be assigned to thestretching vibrations of the OH-groups hydrogen bonded in cela-donite, strictly dependent on the nature of the octahedral cations.OH bending modes involving octahedral cations (R3þeOeH, whereR3þ is the octahedral ion) are responsible for the bands near800 cm�1, which could be assigned to the in-plane bending vibra-tions dMgFe3þOH of celadonite (Anastassopoulou et al., 1997;Newman, 1979), also coinciding with the respective dFe2þFe3þOHmodes (Farmer, 1974). The bands observed at 747 and 675 cm�1 inthe spectrum of sample S13 are related to the R3þeOeH bendingvibrations of celadonite as well (Ospitali et al., 2008; Moretto et al.,2011). A sequence (triplet) of absorption bands is also observedbelow 500 cm�1 (near 440, 460, 488 cm�1), related to the SieOeR3þ and R3þeOH vibrations of celadonite (Newman, 1979; Morettoet al., 2011). These bands are very sensitive to the variation of ionswithin an octahedral coordination in such structures (SieOeR3þ),particularly of Fe3þ.

3.2. In-situ FORS results

The study and comparative analysis of the VIS-NIR diffusereflectance spectra obtained from both Churches for every inves-tigated color impression, led to the following observations andresults regarding the identification of pigments from the TheotokosChurch at Meronas.

3.2.1. Red color impressionsThe diffuse reflectance spectra obtained from the in-situ mea-

surements in the ceramic- and orangeered color impressions areshown in Fig. 8a. The spectra present a typical S-shape character-ized by a sharp positive slope at the wavelengths between 550 and600 nm, a maximum near 740 nm and two absorption bands, astrong one in the blue-green region (near 490 nm) and a weaker inthe near-infrared (between 850 and 870 nm). The first derivativesof the curves were also performed (D0 ¼ DR/dl), as shown in Fig. 8b,identifying that the wavelength of the inflexion point lm, whichwas calculated as the maximum of each derivative spectrum, variesbetween 575 and 580 nm. All these spectral features are charac-teristic for red ochre with the form of hematite (Cheilakou et al.,2009; Picollo et al., 2000; Elias et al., 2006), which was also veri-fied by the ESEM-EDX and ATR-FTIR results of the red samplesdescribed above (x 3.1.2), therefore confirming the use of red ochreby the artist of Meronas for the production of the ceramic- andorange-red colorations.

Concerning the deep and bright red colorations, the reflectancespectra obtained demonstrated in Fig. 9a present different shapecompared with those analyzed above (Fig. 8a) referring to thepresence of a stronger and sharper positive slope near 600 nm,which is characteristic for cinnabar (Clark, 1995). From the calcu-lation of the first-derivative curves (Fig. 9b) lm was evaluated to605 nm coinciding with the inflexion point of HgS (Bacci, 1995).Additionally, as shown in Fig. 9a the spectra corresponding toPatsos (curves 1,2) show weak and broad absorption bands in theblue-green region and in the near-IR (around 850 nm), which couldbe attributed to hematite, suggesting the existence of both cinnabarand red ochre, as found by the ESEM-EDX, ATR-FTIR and micro-Raman results of samples S1 (deep red) and S2 (bright red). Thesharper and stronger positive slope observed in the bright redspectrum (curve 2) could possibly indicate the higher content inHgS, as well. The above features related to hematite are not presentin the spectrum corresponding to Meronas (curve 3), which ischaracterized by a constantly increased slope towards higherwavelengths (600e1000 nm) and the absence of minima in theblue-green region, totally coinciding with the spectral features ofHgS. All the aforementioned data show the use of cinnabar by theMeronas artist for the production of the bright red colorimpressions.

3.2.2. Yellow color impressionsThe diffuse reflectance spectra of the yellow colorations

demonstrated in Fig. 10a present a typical S-shape and similarspectral features with those related to red ochre (Fig. 8a) differingmainly by the sharp positive slope appearing in lower wavelengths(between 500 and 580 nm) with respect to red ochre, as well as thepresence of a broad absorption band near 660 nm. The above fea-tures are characteristic for yellow ochre with the form of goethite(Cheilakou et al., 2009; Picollo et al., 2000; Elias et al., 2006; Clark,1995). The curves are also characterized by a shoulder between 450and 480 nm and a broad absorption band near 930 nm attributed togoethite (Picollo et al., 2000). The first derivative of the spectrademonstrated a maximum varying between 545 and 555 nm(Fig. 10b) corresponding to the wavelength of the inflexion pointlm, which is evaluated to 550 nm for pure goethite and varies

Fig. 7. ATR-FTIR absorption spectra of green samples (a) S11 (green), S12 (dark green) and (b) S13 (green).

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555550

between 535 and 565 nm for yellow ochre (Elias et al., 2006). Theaforementioned results are totally agreeable with the laboratoryanalytical results of the yellow sample (x 3.1.4) verifying the use ofyellow ochre by the artist of Meronas, with goethite as majorcomponent of the pigment, for the production of the yellowcolorations.

3.2.3. Brown color impressionsFig. 11 provides the diffuse reflectance spectra of the dark

purple-brown color impressions along with the spectrum of aceramic-red coloration (curve 2 of Fig. 8a) for comparison purposes.From the comparative spectral analysis it is observed that thecurves of the purple-brown colorations (curves 1,2) approach theshape of the ceramic-red spectrum (curve 3) therefore indicatingthe presence of red ochre (hematite), and differ mainly in the lowreflectance intensity as well as the low positive slope that theyappear between 550 and 600 nm when compared with red ochre.These FORS data combined with the laboratory analytical results ofthe brown samples (x 3.1.3) indicate that the dark purple-brown

colorations are due to red ochre with high hematite content andprobably mixed with black carbon, which results in the afore-mentioned significant decrease of both reflectance intensity andthe slope (between 550 and 600 nm) as well as in the slightbroadening and shifting of the edges in higher wavelengths, whichwere observed in the spectrum of Meronas.

3.2.4. Green color impressionsFrom the comparative spectral analysis demonstrated in Fig. 12,

it is observed that, in general terms, all spectra of the green col-orations present similar shape and are differentiated in theirreflectance intensity. Specifically, the curves corresponding to thewall paintings saved in both Churches (curves 2,3) are character-ized by a reflectance maximum at lmax z 560 nm which lies be-tween two minima (absorption maxima) near 500 and 750 nm,presenting also a secondary broadmaximum in the near-IR (around850 nm) and a shoulder near 480 nm. These spectral features arecharacteristic for green earth pigment (Cheilakou et al., 2009) in theform of celadonite (Hradil et al., 2004). The aforementioned

Fig. 8. (a) Diffuse reflectance spectra of the ceramic- and orangeered color impressions obtained from the wall paintings of the Panagia Church at Patsos (curves 1,2) and theTheotokos Church at Meronas (curves 3,4). (b) First derivative spectrum of the ceramicered color impression from Patsos (curve 2 of a).

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555 551

findings are in accordancewith the ESEM-EDX and ATR-FTIR resultsof the green samples (x 3.1.5) thus, verifying that the green pigmentutilized by the artist of Meronas was green earth (celadonite). As faras curve 1 is concerned that corresponds to the detached wallpainting “Nikolaos” from Patsos, a slight broadening and shift of thereflectance peak in higher wavelengths (near 570 nm) is observed.This could be associated with the small differentiation presented inthe ATR-FTIR spectrum of the respective green sample S13 (takenfrom ‘Agios Nikolaos’ e Fig. 7b) with respect to the spectra ofsamples S11 and S12 (Fig.7a).

3.2.5. Interpretation of the obtained diffuse reflectance spectraThe color of Fe-oxides is mainly a function of the electron

transitions allowed by their structure, also strongly dependent onother factors such as particle size and shape, the degree of particlepacking and absorbed impurities resulting in crystal defects(mainly due to Al-for-Fe substitutions). Red and yellow ochresconsist mainly of hematite and goethite, respectively, and of whitepigments (aluminosilicates) such as kaolinite and quartz, whosevarying contents affect the color of ochres.

The absorption bands exhibited by the Fe-oxides at UV to near IRwavelengths originate from electronic transitions within the 3d5

shell of the Fe3þ ion: i) Fe3þ ligand field transitions, ii) transitionsdue to magnetically coupled Fe3þ cations in adjacent sites and iii)

the ligand-to-metal charge transfer transition (LMCT). The color ofhematite and goethite, which are the major components of red andyellow ochre, respectively, is mainly explained by the LMCT tran-sition 6tlu O2�or�OH�

� �/2t2g Fe3þ

� �. This transition occurs at

energies higher than those of ligand field transitions and producean absorption band in the near UV extending to the lower wave-lengths (blueegreen) of the visible region. In the diffuse reflectancespectra, it induces a reflectance minimum in the UV range and astrong positive slope corresponding to the absorption edge in thevisible range. This strong absorption band is present in the reflec-tance spectra of all the investigated red and yellow color impres-sions (Figs. 8a and 10a) coming from red and yellow ochre,respectively (Elias et al., 2006; Torrent and Barrón, 2002, 2008). Thewavelength lm corresponding to the inflexion point of the ab-sorption edge is indicative of the CT band position, varying from545 to 555 nm (Fig. 10b) and 575e580 nm (Fig. 8b) according to thecomposition of the ochres (Fe-oxides and aluminosilicate com-pounds) and thus to their color (Elias et al., 2006).

The Fe3þ ion presents the 3d5 electronic configuration whichexcites the 6A1g ground state in an octahedral symmetry generatedby the O2� and OH- ligands. Fe 3d atomic orbitals are split into threet2g and two eg orbitals separated by the crystal field splitting energyof 10Dq. Ligand field or ded transitions are ultimately due to thepossible electronic configurations of these orbitals and are the

Fig. 9. (a) Diffuse reflectance spectra of the deep and bright red color impressionsobtained from the wall paintings of the Panagia Church at Patsos (curves 1,2) and theTheotokos Church at Meronas (curve 3). (b) First derivative spectrum of the bright redcolor impression from Patsos (curve 2 of Fig. 9a).

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555552

result of excitations from 6A1g ground state. These transitions are inprinciple both spin and parity forbidden, which, however, areallowed in Fe-oxides through magnetic coupling of electronic spinsof the adjacent Fe3þ ions in the crystal. Additional transitions cor-responding to simultaneous excitations within two adjacent Fe3þ

ions (double excitation) may be present (Torrent and Barrón, 2002,2008).

The single electron transition 6A1g/4T2g induces a weak ab-

sorption band near 640 nm and the 6A1g/4T1g transition induces

absorption bands near 840 and 910 nm for hematite and goethite,respectively. Another 6A1g/

4A1g;4Eg transition appears at 440 nm,

while the electron pair transition 2ð6A1gÞ/2ð4T1gÞ exists at 480 nmfor goethite and 530 nm for hematite (Elias et al., 2006; Torrent andBarrón, 2002, 2008). The above ded transitions are slightly shiftedin the diffuse reflectance spectra of the investigated red and yellowcolor impressions (Figs. 8a and 10a). This is mainly due to Al-for-Fesubstitutions resulting in decreased symmetry of the Fe(O,OH)6octahedra symmetry, which in turn alter the ligand field and shiftband positions. For instance, the 6A1g/

4T1g transition of goethitenormally occurring at 910 nm is shifted to higher wavelengths(lower energy) near 930 nm, as shown in Fig. 10a. This could beattributed to Al incorporation (from kaolinite) into the goethitestructure, subsequently resulting in the decrease of the Fe-(O,OH)

distances (Scheinost et al., 1999). Similarly, differences in the Fe-to-Fe distance may affect magnetic coupling of the neighbor Fe3þ ionand, as a consequence, the position and intensity of the doubleexcitation band.

The CT absorption coefficient is around 105 times larger than forded transitions. Moreover, the more ionic the bond between Fe3þ

and the ligands (i.e. the more electronegative the ligand) the moreshift of the CT band towards lower wavelengths. This could explainthe fact that lm and the CT band position alter with composition ofthe ochres and are themajor factors of the different color variations(Elias et al., 2006).

The red color of HgS is caused by the electronic transitionsoccurring from the lower energy valence band, where electrons areattached to individual atoms, to the higher energy conductionband, where electrons move freely throughout the lattice. Thedifference between these energy levels is called the band gap,which in semiconductors as HgS, corresponds to the energy ofvisible or near IR photons producing the electron excitation (Clark,1995). This band gap induces a very sharp positive slope in thevisible range (near 600 nm) of the cinnabar diffuse reflectancespectra, which also appears in the spectra of the examined brightred color impressions (Fig. 9a).

The color of green earth minerals, such as celadonite, is affectedby several ded ligand field transitions and intervalence chargetransfer transitions (IVCT) between Fe2þeFe3þ ions. The diffusereflectance spectra of green earths are characterized by the pres-ence of a reflectance maximum near 555 nm lying between twominima (absorption bands) around 500 and 750 nm. The lattercould be explained by the IVCT Fe2þeFe3þ and the electronictransition 6A1g/

4T2g of the tetrahedral Fe3þtetra, respectively(Hradil et al., 2004; Sànchez- Navas et al., 2008). The aforemen-tioned spectral features appear in the diffuse reflectance spectra ofthe investigated green colorations (Fig. 12) which come from greenearth pigment in the form of celadonite.

4. Conclusions

In this study, the characterization of Byzantine wall paintings(14th Century) of two Churches from Rethymno, Crete, wasattempted by means of an analytical methodology that combinedFORS portable instrumentation with laboratory techniques. Theresults obtained allowed for the first time to gain a deep knowledgeof the wall painting materials and techniques adopted duringByzantine period in Crete, thus constituting of fundamental scien-tific, technological and archaeological significance.

The ESEM-EDX, ATR-FTIR and micro-Raman techniques thatwere applied for the analysis of the micro-samples collected onlyfrom the Panagia Church at Patsos, Amari, were complementaryleading to reliable conclusions concerning the identification ofpigments, organic binders and the technique applied for the con-struction of the wall paintings, as well as degradation phenomena.The color palette of the Byzantine artist was found to comprisetypical fresco pigments such as calcite, red and yellow ochre (he-matite, goethite), green earth (celadonite), cinnabar and amor-phous carbon of vegetable origin, as well as their mixtures for theproduction of the desirable color hues. The presence of calcitecombined with the protein binding medium (likely associated withegg) identified in all samples showed the employment of a mixedwall painting technique involving both fresco and secco.

The results obtained from the in-situ FORS measurements onboth Churchmurals, indicated the effectiveness of VIS-NIR FORS forthe characterization of the wall painting pigments decorating theChurch in Meronas, from which no sampling was allowed. Thecomparative study that was carried out between the diffusereflectance spectra collected from both Churches and the

Fig. 10. (a) Diffuse reflectance spectra of the yellow color impressions obtained from the wall paintings of the Panagia Church at Patsos (curve 1) and the Theotokos Church atMeronas (curve 2). (b) First derivative spectrum of the bright yellow color impression from Patsos (curve 1 of Fig. 10a).

Fig. 11. Diffuse reflectance spectra of the brown color impressions obtained from thewall paintings of the Panagia Church at Patsos (curve 1) and the Theotokos Church atMeronas (curve 2). The spectrum of a ceramic-red coloration from the Patsos Church(curve 3) is also presented for comparative analysis.

Fig. 12. Diffuse reflectance spectra of the green color impressions obtained from thewall paintings of the Panagia Church at Patsos (curves 1,2) and the Theotokos Church atMeronas (curve 3).

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555 553

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555554

laboratory analysis results, established the reliability of theanalytical information obtained from the portable instrumentationproviding accurate identification of the pigments and/or theirmixtures utilized by the artist of Meronas. These were found to beof the same compositionwith those comprising the Patsos painter’scolor palette.

Finally, the results obtained from this research work confirmedthat VIS-NIR FORS could be used as a valuable and appropriate non-invasive tool for the in-situ characterization of pigments, offeringkey advantages such as instrument mobility and speed of datacollection and interpretation that enable rapid surveying of thewallpaintings in an effective manner, thus contributing significantly totheir conservationerestoration procedures.

Acknowledgments

Acknowledgments are attributed to the Doc-Culture researchproject entitled “Development of an Integrated Information Envi-ronment for assessment and documentation of conservation in-terventions to cultural works/objects with Non DestructiveTechniques (NDTs)”, which is coordinated and managed by NTUA.MIS: 379472. The 3-year project began in April 2012 and is co-financed by the European Union (European Social Fund e ESF)and Greek national funds through the Operational Program “Edu-cation and Lifelong Learning” of the National Strategic ReferenceFramework (NSRF) e Research Funding Program: THALES. Invest-ing in knowledge society through the European Social Fund. Wewould like to express our thanks to both Referees, who with theirinteresting questions and remarks together with their excellentsuggestions improved greatly the presentation of our work. Greatthanks are attributed to Honorary Professor Theophile Theopha-nides of National Technical University of Athens and University ofMontreal for his significant help with the manuscript.

References

Aliatis, Bersani, Campani, Casoli, Lottici, Mantovan, Marino, Ospitaly, 2009. Greenpigments of the Pompeian artists’ palette. Spectrochim. Acta A Mol. Biomol.Spectrosc. 73, 532e538.

Anastassopoulou, Koui, Yfantis, Theophanides, 1997. The use of FT-IR Spectroscopyfor surface analysis for atmospherically polluted ancient marbles. In: Proc. ofthe 4th Intern. Symposium on the Conservation of Monuments in the Medi-terranean, Rhodes, Greece, vol. 2, p. 24.

Andrianakis, 2002. The Church of Panagia in Patsos of Amari. Crete, Tour in Natureand Culture. Technical Report. Project TERRA DIAS, Heraklion, Greece, pp. 223e228 (in Greek).

Appolonia, Vaundan, Chatel, Aceto, Mirti, 2009. Combined use of FORS, XRF andRAMAN spectroscopy in the study of mural paintings in Aosta Valley (Italy).Anal. Bioanal. Chem. 395, 395e2013.

Bacci, 1995. Fiber optics applications to works of art. Sens. Actuat. B 29, 190e196.Bacci, 2006. Non-invasive instrumentation for detection and color control of

paintings and artworks. Archaom. Mühely 1, 46e50.Bikiaris, Daniilia, Sotiropoulou, Katsimbiri, Pavlidou, Moutsatsou, Chryssoulakis,

1999. Ochre-differentiation through micro-Raman and micro-FTIR spectros-copies: application on wall paintings at Meteora and Mount Athos, Greece.Spectrochim. Acta A Mol. Biomol. Spectrosc. 56, 3e18.

Borboudakis, 1986. The murals of Panagia (Virgin) in Meronas and a definite trendof Cretan painting. In: Proceedings of 5th International Cretological Conference,Agios Nikolaos, Heraklion, Greece, vol B, pp. 396e412 (in Greek).

Bouchard, Smith, 2003. Catalogue of 45 reference Raman spectra of minerals con-cerning research in art history or archaeology, especially on corroded metalsand coloured glass. Spectrochim. Acta A Mol. Biomol. Spectrosc. 59, 2247e2266.

Bougeard, Smirnov, Geidel, 2000. Vibrational spectra and structure of kaolinite: acomputer simulation study. J. Phys. Chem. B 104, 9210e9217.

Cheilakou, Kartsonaki, Koui, Callet, 2009. A Non Destructive study of the identifi-cation of pigments on monuments by colorimetry. Int. J. Microstruct. Mater.Prop. 4 (1), 112e127.

Clark, 1995. Reflectance spectra, rock physics and phase relations. In: Handbookof Physical Constants. Published by the American Geophysical Union,pp. 178e188.

Daniilia, Sotiropoulou, Bikiaris, Salpistis, Karagiannis, Chryssoulakis, Priced, Carl-sone, 2000. Panselinos’ Byzantine wall paintings in the Protaton Church, MountAthos, Greece: a technical examination. J. Cult. Herit. 1, 91e110.

Daniilia, Minopoulou, Andrikopoulos, Tsakalof, Bairachtari, 2008. From Byzantine topost-Byzantine art: the painting technique of St Stephen’s wall paintings atMeteora, Greece. J. Archaeol. Sci. 35, 2474e2485.

Derrick, Stulik, Landry, 1999. Infrared Spectroscopy in Conservation Science e Sci-entific Tools for Conservation. J. Paul Getty Conservation Institute, USA.

Dupuis, Elias, Simonot, 2002. Pigments identification by fiber optics diffusereflectance spectroscopy. Appl. Spectrosc. 56 (10), 1329e1336.

Edwards, Chalmers, 2005. Raman Spectroscopy in Archaeology and Art History.Published by The Royal Society of Chemistry, UK.

Elias, Chartier, Prévot, Garay, Vignaud, 2006. The colour of ochres explained by theircomposition. Mater. Sci. Eng. B 127, 70e80.

Farmer, 1974. The Infrared Spectra of Minerals. Published by Mineralogical SocietyMonograph 4, London, UK.

Fernández-Carrasco, Torrens-Martín, Morales, Martínez, Ramírez, 2012. Infraredspectroscopy in the analysis of building and construction materials. In:Theophanides, T. (Ed.), Infrared Spectroscopy, Materials Science, Engineeringand Technology. INTECH, pp. 369e382.

Frost, Fredericks, Bartlett, 1993. Fourier Transform Raman spectroscopy of kanditeclays. Spectrochimica Acta 49A (5/6), 667e674.

Gerola, 1905. Monumenti Veneti nell’ Isola di Creta. Istituto Veneto di Scienze,Lettere Ed Arti, Venice.

Gunasekaran, Anbalagan, Pandi, 2006. Raman and infrared spectra of carbonates ofcalcite structure. J. Raman Spectrosc. 37, 892e899.

Hein, Karatasios, Mourelatos, 2009. Byzantine wall paintings from Mani (Greece):microanalytical investigation of pigments and plasters. Anal. Bioanal. Chem.395, 2061e2071.

Hlavay, Jonas, Elek, Inczedy, 1978. Characterization of the particle size and thecrystallinity of certain minerals by IR spectrophotometry and other instru-mental methods e II. Investigations on Quartz and Feldspars. Clay Miner. 26 (2),139e143.

Hradil, Grygar, Hru�sková, Bezdi�cka, Lang, Schneeweiss, Chvátal, 2004. Green earthpigment from the Kada�n Region, Czech Republic: Use of rare Fe- rich smeltice.Clay Clay Miner. 52 (6), 767e778.

Iordanidis, Garcia-Guinea, Strati, Gkimourtzina, Papoulidou, 2011. Byzantine wallpaintings from Kastoria, northern Greece: spectroscopic study of pigments andefflorescing salts. Spectrochim. Acta A Mol. Biomol. Spectrosc. 78, 874e887.

Kalokyris, 1973. In: Hionides, H., Gunderson, J. (Eds.), The Byzantine Wallpaintingsof Crete. Published by Red Dust Inc, New York.

Legodi, de Waal, 2007. The preparation of magnetite, goethite, hematite andmaghematite of pigment quality frommill scale ironwaste. Dyes Pigm. 74, 161e168.

Madejová, 2003. FTIR techniques in clay mineral studies, Review. Vibrat. Spectrosc.31, 1e10.

Mamarelis, Pissaridi, Dritsa, Kotileas, Tsiligiris, Tzilalis, Anastassopoulou, 2010.Oxidative stress and atherogenesis an FT-IR spectroscopic study. In Vivo 24,883e888.

Meilunas, Bentsen, Steinberg, 1990. Analysis of aged painted binders by FTIRspectroscopy. Stud. Conserv. 35, 33e51.

Moretto, Orsega, Mazzocchin, 2011. Spectroscopic methods for the analysis ofceladonite and glauconite in Roman wall paintings. J. Cult. Herit. 12 (4), 384e391.

Newman, 1979. Some applications of infrared spectroscopy in the examination ofpainting materials. J. Am. Inst. Conserv. 19 (1), 42e62.

Ospitali, Bersani, Di Lonardo, Lottici, 2008. ‘Green earths’: vibrational and elementalcharacterization of glauconites, celadonites and historical pigments. J. RamanSpectrosc. 39, 1066e1073.

Pavlidou, Arapi, Zorba, Anastasiou, Civici, Stamati, Praskevopoulos, 2006. Onoufrios,the famous XVI’s century iconographer, creator of the “Berati School”: studyingthe technique and materials used in wall paintings of inscribed churches. Appl.Phys. A 83, 709e716.

Perardi, Appolonia, Mirti, 2003. Non destructive in situ determination of pigmentsin 15th century wall paintings by Raman microscopy. Anal. Chim. Acta 480 (2),317e325.

Picollo, Bacci, Casini, Lotti, Porcinai, Radicati, Stefani, 2000. In: Martellucci, et al.(Eds.), Fiber Optics Reflectance Spectroscopy, a Non-destructive Technique forthe Analysis of Works of Art, Optical Sensors and Microsystems: New Concept,Materials, Technologies. Kluwer Academic/Plenum Publishers, New York,pp. 259e265.

Ramasamy, Suresh, 2009.Mineral characterization and crystalline nature of quartz inPonnaiyar River sediments, Tamilnadu, India. Am. Eur. J. Sci. Res. 4 (2), 103e107.

Sànchez-Navas, Martín-Algarra, Eder, Jagannadha, Nieto, Zanin, 2008. Color,mineralogy and composition of upper west Siberian Glauconite: useful in-dicators of paleoenvironment. Can. Miner. 65, 1545e1564.

Scheinost, Schulze, Schwertmann, 1999. Diffuse reflectance spectra of Al substitutedgoethite: a ligand field approach. Clay Clay Miner. 47, 156e164.

Schroeder, 2002. Infrared spectroscopy in clay science. In: Rule, A., Guggenheim, S.(Eds.), CMS Workshop Lectures, Teaching Clay Science, vol. 11. The Clay MineralSociety, Aurora, CO, pp. 181e206.

Silva, 2003. Properties of amorphous carbon. Chapter: Raman Spectroscopy of a-C.Authors Ferrari, A. C. & Prawer, S.. INSPEC publications, UK, p. 46.

Taft, Mayer, 2000. The Science of Paintings. Springer-Verlag, New York.Theophanides, Anastasopoulou, 2010. Monument damage from environmental

pollution of ancient marbles using spectroscopic technologies. In: Proc. the 8thInternational Symposium on the Conservation of Monuments in the Mediter-ranean Basin, Patras, Greece, vol. 2, pp. 131e141.

E. Cheilakou et al. / Journal of Archaeological Science 41 (2014) 541e555 555

Theophanides, Angiboust, Manfait, 1988. Protein and nucleic acid changes. In:Twardowski (Ed.), Spectroscopic and Structural Studies of Biomaterials, I. Pro-teins. Sigma Press, Wilmslow, UK, pp. 3e12.

Thompson, 1998. The Materials and Techniques of Medieval Painting, first ed. 1936.Armos Pupl., Athens, Greece.

Torrent, Barrón, 2002. Diffuse Reflectance Spectroscopy of Iron Oxides. In: Ency-clopedia of Surface and Colloid Science, pp. 1438e1446.

Torrent, Barrón, 2008. Methods of Soil Analysis, Part 5 Mineralogical Methods. In:Chapter 13: Diffuse Reflectance Spectroscopy. SSSA Book Series, no. 5. USA,pp. 367e385.

Westlake, Siozos, Philippidis, Apostolaki, Derham, Terlixi, Perdikatsis, Jones, Anglos,2012. Studying pigments on painted plaster in Minoan, Romanand EarlyByzantine Crete. A multi-analytical technique approach. Anal. Bioanal. Chem.402, 1413e1432.