Analytical characterization of recently excavated megalithic sarcophagi potsherds in Veeranam village, Tiruvannamalai dist., Tamilnadu, India

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 845–853

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Analytical characterization of recently excavated megalithic sarcophagi potsherds in Veeranam village, Tiruvannamalai dist., Tamilnadu, India R. Ravisankar a,⇑, G. Raja Annamalai b, A. Naseerutheen c, A. Chandrasekaran d, M.V.R. Prasad e, K.K. Satpathy e, C. Maheswaran f a

Post Graduate and Research Department of Physics, Government Arts College, Tiruvannamalai 606 603, India Department of Physics, Shri Krishnaa College of Engineering & Technology, Mannadipet, Puducherry 605 501, India Department of Physics, C.Abdul Hakeem College, Melvisharam, Tamilnadu 632 509, India d Department of Physics, Global Institute of Engineering & Technology, Vellore, Tamilnadu 632 509, India e Environmental and Safety Division, Reactor Engineering Group, Radiological Safety & Environmental Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India f Anthropology Section, Government Museum, Egmore, Chennai 600 008, India b c

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 We report the manufacture skills and

Factor score 1 versus factor score 3 of pottery samples of Veeranam village, shows the three distinct groups are formed.

technology of ancient potteries.  We report the firing condition and temperature of potteries.  The statistical tools applied to identify the provenance and potteries groups.

0.8 Pb

0.6

A V

B

0.4

Cu

Al203

C

0.2

Co Fe2O3 Sio2

caO Factor 3

0.0 -0.2

Tio2 K2O Cd

La

Cr

-0.4 -0.6 -0.8 Zn -1.0 -1.2 -0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Factor 1

a r t i c l e

i n f o

Article history: Received 4 March 2013 Received in revised form 20 June 2013 Accepted 28 June 2013 Available online 8 July 2013 Keywords: Pottery Mineral Analysis TG-DTA SEM-EDX ED-XRF Statistical Analysis

a b s t r a c t Analytical characterization of megalithic sarcophagi potsherds from Veeranam, Tiruvannamalai dist., Tamilnadu has been performed using Fourier transform infrared spectroscopy (FTIR), Powder X-ray diffraction (PXRD), Thermal analysis (TG-DTA), Scanning Electron Microscopy (SEM) coupled with an energy-dispersive X-ray spectrometer (EDX) and Energy dispersive X-ray fluorescence spectrometry (EDXRF). The EDXRF data of the potsherds were processed using multivariate statistical methods. Principal Component Analysis (PCA) and hierarchical cluster analysis allow us to identify grouping and structure in the data. The analytical results achieved in this study allowed us to estimate the firing temperature and manufacturing techniques. The methodological approach was successfully applied to the mineralogical, chemical and thermal characterization of the potsherds. Crown Copyright Ó 2013 Published by Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +91 9443520534; fax: +91 4175 236553. E-mail address: [email protected] (R. Ravisankar). 1386-1425/$ - see front matter Crown Copyright Ó 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.06.123

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Introduction Archaeometry is a multidisciplinary research branch, which focuses on studying and solving problems in the field of cultural heritage [1]. This discipline is geared towards the extraction of information about the genesis and history of finds, through the analysis of the material (which refers to their chemical structure and modifications) and dating techniques. Archaeometry includes studies about dating, authentication, firing temperature, conservation and restoring, provenance and the achievement of technological information about handmade articles manufacture as well. Potteries have a long history and are found in almost all societies. They are not perishable, and are often found in large quantities in archaeological excavations. Chemical analysis and technical examination of art works play an essential role in providing historical, artistic and technical information. It is important to furthering the understanding of our cultural heritage, notably in connection with the restoration, conservation, dating and authentication of artefacts. In the past 25 years, and especially in the last decade, the techniques have been increasingly applied in the identification of the archaeology. Among these, non-destructive methods, which leave the sample viable and undisturbed and allow monitoring over a long period of time, are of great interest. One of the most important questions asked by archaeology is the provenance of the excavated object, since any archaeological item could have been produced locally at the place where it was found or transported to the site from a location where it was originally manufactured. Identification of the excavated material origin is by no means easy and straight forward. Only the power of combined analytical techniques allows for confident and detailed establishment of the geographical origin of the raw material used to manufacture the investigated object. The application of analytical methods to the study of ancient pottery has proved to be a valuable complement to archaeological investigations, aiming to reconstruct the ceramic life cycle, i.e. to extract provenance information and rediscover manufacture technology and use [2]. Provenance is normally assessed by elemental analyses followed by appropriate statistical handling in order to identify ceramic groups of similar chemical profiles and to assign each of the detected groups to a certain production center. Manufacture technology involves several aspects of pottery making, such as the type of raw materials used, their processing to prepare the clay paste, the surface treatment, decoration and firing to obtain the finished item. Among a long list of instrumental techniques, X-ray analytical methods, including X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD) and scanning electron microscopy coupled with Energy-dispersive X-ray spectroscopy (SEM-EDX), may successfully address the above issues [3–9]. In the growing number of recently reported applications FT-IR spectroscopy is used to estimate the firing conditions and the mineralogical compositions [10–12]. These techniques have proven very powerful for identification and characterization of small amounts of samples. The mineralogy, the microstructure and chemical composition of the red sliped megalithic sarcophagi potsherds from Veeranam, Tiruvannamalai dist., Tamilnadu examined by FT-IR, PXRD, DTATG, SEM-EDX and EDXRF spectroscopy, respectively, in order to probe manufacturing skills and choices with statistical approach.

13°480 N; long 80°1000 E) India by the Government Museum, Egmore, Chennai, Tamilnadu, India. The samples were collected at 8 m from the surface of the soil. The pottery shreds of Veeranam village belonging between 100 BC and 300 AD in South India. Red slipped ware was collected in the site. All the fragments collection of same variety and color1. The typical collection of pottery samples is shown in Fig. 1. The samples are labeled as TP1, 2, 3, 4 5 and 6. After removal of surface layers, the pottery shreds were ground into fine powder using agate mortar. This fine powered is used for different analyses. Analytical instrumentation and methods Fourier-transformed infrared spectroscopy The IR spectrum of the samples was recorded using Perkin Elmer 16000 series spectrometer in the region of 4000–400 cm1 in the received state as well as refired state at room temperature. The KBr pellet technique was followed by mineral analysis. The instrument scans the spectra 16 times in 1 min and the resolution is ±5 cm1. This instrument is calibrated for its accuracy with the spectrum of a standard polystyrene film. A typical FT-IR spectrum is shown in Fig. 2. Powder X-ray diffraction Samples for X-ray powder diffraction (XRD) studies were packed in shallow cavities in glass slides to minimize preferred orientation. The X-ray patterns of pottery samples were recorded at room temperature by using X-ray diffractometer (D500, Siemens) having a curved graphite crystal diffracted monochromator, with a source of Cu Ka radiation and NaI(Tl) scintillation detector from Department of Nuclear Physics, Madras University, Chennai, Tamilnadu, India. Experiments were performed at steps of (2h) 0.02° and a counting time of 1.0 s/step. Qualitative mineralogy of the studied samples is determined with the standard interpretation procedures of XRD. Thermal analysis (DTA-TG) Thermal analysis that includes thermogravimetric (TG) investigations and differential thermal analysis (DTA) has been performed using DERIVATOGRAPH 1500Q. The data were collected up to 800 °C with increments of 10 °C/min. Scanning electron microscopy Information on surface morphology of the samples was obtained by using SEM Quanta FEI, Netherland. The maximum magnification possible in the equipment is 300,000 times with the resolution of 3 nm. The elemental analysis was done using the Oxford INCA Energy Dispersive X-ray Fluorescence Spectrometer (EDX). The fired state sample coated with a thin layer of platinum was examined using SEM, typically setting at a magnification of X2000 for all the samples of the study.

Sample collection

Energy dispersive X-ray spectrometry The powder samples were dried at 110 °C in an oven until no further weight loss was observed. One gram of the fine ground sample and 0.5 g of the boric acid were mixed. The mixture was thoroughly ground and pressed to a pellet of 30 mm diameter using a 15 ton hydraulic press. The prepared samples were analyzed using the EDXRF available at Environmental and Industrial Safety Section, Safety Group, Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam, Tamilnadu. The instrument used for this study is a PW 4025 Minipal supplied by M/s Philips,

The pottery samples were recently excavated from the site Veeranam village of Thandrampet Taulk, Tiruvannamalai, (lat.

1 For interpretation of color in Fig. 1, the reader is referred to the web version of this article.

Materials and methods

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Fig. 1. The typical collection of Veeranam potsherds.

Fig. 2. A typical FT-IR spectrum of potsherds of Veeranam.

Netherlands. The spectrometer is fitted with a side window X-ray tube (9 W) that has Rhodium as anode. The power specifications of the tube are 4–30 kV; 1 lA–1 mA. Removable sample changer of the instrument accommodates 12 samples at a time. Selection of filters, tube voltage, sample position and current are fully computer controlled. Beam spot area (elliptical) for the instrument is 81.7 mm2. The instrument has the features of Multi Channel Analyzer (MCA) test, standardless determination and automatic gain correction. Gain correction is performed when the beam stop is in the reference position. Beam stop contains a reference sample (an alloy of aluminum and copper). Copper is used for gain correction. Al and Cu are used for instrument energy calibration. Statistical treatment of chemical composition data Data of chemical composition were submitted to a statistical treatment by multivariate chemometric techniques to verify the presence of groups of samples having similar compositional features. Two unsupervised methods were used to show the overall structure of the six samples in a multidimensional space. Hierarchical Cluster Analysis (HCA), using the single linkage method for building up dendrograms and Principal Component Analysis (PCA) using the varimax normalized method are used to compute principal components. Elemental compositions were submitted to PCA after normalizing to log base 10 values. The transformation is often applied to smooth out difference in magnitude between major and trace

elemental concentration. In this work Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) have been done by using STATISTICA (version10.0) software package for windows. Results and discussions FT-IR spectroscopy FT-IR spectra reveal the presence of quartz in all investigated samples identified by the peaks at 455, 695, 775 and 795 cm1. The presence of quartz in the sample can be explained by Si–O symmetrical stretching vibrations at around 775 and 795 cm1 while Si–O symmetrical bending vibrations arise around 695 cm1 due to low level of Al for Si substitution. According to Elsass and Oliver [13], the presence of the sharp band at 695 cm1 indicates thin particles and in the case of thick particles, this band has shifted to 689 cm1. Since the red clay shows this band at 695 cm1 it is clear that this clay contains quartz of thin particle size. Two weak peaks at 2855 and 2925 cm1 [10] belong to C–H stretching vibrations indicate the presence of organic material. Clay deposits generally contain variable amounts of organic matter, but organic additives can also be used by potters during preparation of the ceramic paste, in order to achieve more plasticity. In addition, organic matter can also be deposited during use of ceramic tableware or during the burial period. The amount of the

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organic contribution is higher in red part in comparison with the black decoration part [14]. Our samples are also red in color which supports the statement. Spectrum reveals albite (405 and 645 cm1), microcline (425 cm1), kaolinite (1035 cm1), montmorillonite (1635 and 3435 cm1) and hematite (535 and 475 cm1). The assignment has been made on the basis of the characteristic IR wave numbers of the minerals [10–12,15,16]. The presence of bands at 3435 cm1 and 1635 cm1 are assigned to water, most probably originating from hydration of oxides in the ceramic body during the burial period. The presence of clay minerals contributes to the intensity of the hydroxyl stretching band at 3440 cm1 but it is difficult to distinguish these two contributions. The presence of a band at 1035 cm1 of kaolinte is assigned to Si–O stretching mode of silicates and it indicates that the samples have been fired above 750 °C and made up of disordered clay [14]. As stated by Mendelovici [17] and Kakali et al. [18] kaolinite dehydroxylates and transforms to metakaolinite at about 450–650 °C. Metakaolinite has broad vibrational bands around 1098 cm1 (Si–O stretching), 826 cm1 (Al–O stretching) and 469 cm1 (Si–O in plane bending). We did not observe any kaolinite transformation in the IR study. IR spectroscopic results indicated that all samples do not contain calcite. This indicate they are non-calcareous. Decomposition of calcite in clayey matrixes begins at 600 °C mainly occurs around 650–750 °C [19,20]. At higher temperatures (900 °C), high temperature calcium-silicate phases appear; plagioclase-anorthite [CaAl2Si2O8], melilite–gehlenite [Ca2Al(AlSi)O7], pyroxene-diopside [CaMg(SiO3)2] are formed due to thermal reaction of the calcite decomposition products with the fired clay [10]. After firing, deformed calcite may be recarbonated from the remaining decarbonation products of original calcite and/or by a reaction with atmospheric CO2 [10]. Reformed calcite is characterized by a broad

Table 1 Mineralogical composition of potsherds from Veeranam. S.No.

Minerals

TP1

TP2

TP3

TP4

TP5

1 2 3 4 5 6

Quartz Microcline Orthoclase Albite Hematite Magnetite

a

a

b

a

b

a

c

–

c

b

c

c

– –

c

– –

–

Trace = tr, absent = –. a Very abundant. b Abundant. c Present. d Little present.

–

c

b

–

–

c

c

– –

c

–

d

c

TP6

c

c

c

–

d

band around 1450 cm1, although at original calcite this CO3 stretching vibration occurs around 1420–1430 cm1. The vibrational wave number of carbonate stretching vibration is observed around 1418–1430 cm1. We did not observed any firing minerals that (calcium-silicate phases) that originate as the decomposition product of calcite. Thus, depending on the IR spectroscopic results, calcite mineral is estimated to be primary and is present as impurity of the local clays. Observation of calcite (CaCO3) bands allows us to draw conclusion on firing temperature. The presence of the band at 475 cm1 in the received state in all samples indicates presence of iron oxide (hematite) and also they were all fired above 750 °C. The presence of a band at 535 cm1 attributed to Si–O–Al bending vibration is due to the presence of residual Al in octahedral sheet. The presence of hematite is identified by the peaks at 535 and 475 cm1 being an indication of iron oxides formed during firing processes. The results of FT-IR analysis of all sarcophagi revealed that they were fired in open-air and also due to open-air firing technique the samples are not fired uniformly. Table 1 gives the mineralogical characterization details in Veeranam potsherds of Tamilnadu. FT-IR study of refired samples All the samples show absorption at 3440 cm1 along with 1635 cm1 attributed to absorbed water in received state. The absence of inner hydroxyl absorption band at 3690 cm1 and 3620 cm1 in the received state of all the samples indicate that these samples were fired above 450 °C. The broad symmetrical band centered around 1035 cm1 indicates the destruction of octahedral sheet revealing that all the samples were fired above 600 °C. The presence of the band at 475 cm1 in the received state in all samples indicates that they were all fired above 750 °C. To narrow the gap between the two limits of firing temperature a refiring study was conducted. For this purpose the samples were fired in the laboratory to temperatures of 250 °C, 500 °C and 750 °C for one hour using muffle furnace. The spectra were then recorded with these refired samples. A typical FT-IR spectrum of refired spectrum is shown in Fig. 3. The main difference between the IR spectra of the original ancient pottery fragments and the corresponding refired ones is the appearance of firing mineral signatures in the latter spectrum. A comparison of the spectra of refired samples with that of the ‘as received state’ samples reveal the following. The spectra of the samples show the absorption bands at 3435 and 1635 cm1are attributed to absorbed water molecules and get diminished at 250–750 °C. The broad symmetry band centered around 1035 cm1 indicates that the destruction of octahedral sheet structure has taken place around 650 °C. The presence of

Fig. 3. A typical FT-IR spectrum of refired potsherds of Veeranam.

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Table 2 Estimation of firing temperature of pottery shreds excavated at Veeranam, Tiruvannamalai dist. Sample ID

Color

Type of the clay

Atmosphere prevailed

Octahedral sheet structure

Estimation of firing temperature (°C)

TP1

Red Ware Red Ware Red Ware Red Ware Red Ware Red Ware

Red clay Red clay Red clay Red clay Red clay Red clay

Oxidizing

Completed

>800

Oxidizing

Completed

>800

Oxidizing

Completed

>800

Oxidizing

Completed

>800

Oxidizing

Completed

>800

Oxidizing

Completed

>800

TP2 TP3 TP4 TP5 TP6

Fig. 4. A typical PXRD spectrum of Veeranam potsherds.

the band at 1035 cm1 in the received state spectra of samples indicates that they were made up of red clay. In the received state, the presence of the band at 535 cm1 indicates the presence of iron oxides. At 250 °C water evaporates and the intensity of the both bands remains the same up to 750 °C. It indicates that they were fired above 750 °C under open atmosphere and it is well established from the red color of the pottery. The sharp band at 775 cm1 indicates that it belongs to red clay type with more amount of crystalline quartz present in the sample. The spectra of all the samples show a common feature in the region 3435 cm1 and 1635 cm1 which are attributed to absorbed water molecules. From the above observations, these samples were fired under open atmospheric conditions with firing temperature of above 750 °C which is also reflected from the red color of the pottery. The presence of quartz in the samples indicates the coarse materials like sand with more iron content. The above results are valid if quartz and feldspar are present in the potsherds samples in the received as well as refired state. The presence of these minerals may indicate a temperature of at least 900 °C [7]. These two minerals persist on firing up to 1000 °C [21] and thus they are obviously constituents of a silica-rich raw clay material. Quartz may be an indigenous mineral in natural clay or may be an intentionally added temper [22]. This may be inferred by considering the diagnostic peak of quartz at 775 cm1 remaining constant in the received state and also persisting up to 750 °C in the refired samples. This gives a clear indication that all the samples were fired above 750 °C. This result also confirms the firing temperature analysis of FT-IR study of the refired samples. Table 2 list the estimation of firing temperature of Pottery Shreds excavated at Veeranam, Tiruvannamalai dist. PXRD analysis The typical PXRD spectrum is shown in Fig. 4. Powder diffraction patterns of the selected samples are dominated by reflections of quartz. In addition, at least one phyllosilicate (muscovite) and feldspar (albite and orthoclase) were detected in most samples. When clays are thermally treated to make pottery, new minerals (so called firing minerals) are formed. The identity of the products depends mostly on the initial composition of clays and any additives used the firing temperature, atmosphere and duration. Gehlenite and diopside are firing minerals obtained as products of high temperature reactions: gehlenite is obtained from decomposition products of illite and calcite at 800–850 °C [23,24]) and diopside is formed from illite, calcite and quartz at 850–900 °C [25]. Hematite, identified as a crystalline phase in samples, indicates an oxidizing kiln atmosphere.

On the basis of both its mineralogical content observed in the samples, the high quartz content and absence of calcite shows the samples are typical of non-calcareous clays. This indicates is correlated with FT-IR study. Further the presence of phyllosilicates indicates that the firing temperatures did not exceed 900 °C [11]. The data obtained for the investigated samples show that the samples do not contain illites suggesting that pottery has been burned at temperatures 560 °C and above [26]. Hence the firing temperature of potsherds may above 750 °C from the above indings. Presence of Fe (III)-containing hematite in most samples suggests that the artifacts were manufactured by firing in an oxidizing atmosphere. PXRD data analysis can also provide some insight into the production processes used to manufacture these artifacts and also it supports the findings of FT-IR study.

Thermogravimetric analysis (TGA) DTA and TG analysis reveal changes in samples weight as well as in thermodynamic properties. TGA is commonly employed in research to determine characteristics of investigated materials, degradation temperatures, absorbed moisture content of materials and the level of inorganic and organic components in materials and solvent residues [23]. The results of thermo gravimetric analysis of investigated samples are shown in Fig. 5. The data obtained for all investigated pottery groups were similar. The pattern shown by TG curve suggest mass loss during the burn process however there is no more mass loss observed above 560 °C. Combined TG and DTA data show two stages of material decomposition appearing during the burn above 750 °C. Both stages are displayed by changes in thermodynamic properties of investigated samples appearing during burn process. In lower temperatures the most probable reason for mass loss is evaporation of water and in the temperatures 200– 560 °C [27] all the organic remains originating from ceramic use are being destroyed. Although, exposition of investigated clays to temperatures above 560 °C does not cause any mass loss the DTG and DTA curves are displaying changes suggesting chemical reactions within clay components. The FT-IR and PXRD results are well agreement with the TG-DTA results.

SEM-EDX analysis The SEM microstructure of the samples provides a basis for inferring firing temperatures. The typical photos are shown in Fig. 6. Following the main stages of viritification established by

850

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10 .0 0

9 9 .5 0

438.2Cel 8.77uV

9 .0 0

9 9 .0 0

8 .0 0

4.59%

9 8 .5 0

7 .0 0 9 8 .0 0

5 .0 0

9 7 .5 0

4 .0 0

9 7 .0 0

3 .0 0 2 .0 0

TG %

DTA uV

6 .0 0

9 6 .5 0

34.5Cel 1.67uV

9 6 .0 0

1.0 0 9 5 .5 0

0 .0 0 100.0

200.0

300.0

400.0

500.0

600.0

700.0

9 5 .0 0 800.0

Temp Cel Fig. 5. Typical TG-DTA spectrum of Veeranam potsherds.

Fig. 6. A typical SEM micro-photograph of Veeranam potsherds.

Manitatis and Tie [5], the shred TP1 appears initial to extensive viritification. In the potteries, most of these carbonates and clay minerals are present in the cooking ware samples. Their presence in the pottery samples indicates that it was fired at a relatively low temperature. While kaolinite loses its stability rather abruptly at 500–600 °C, montmorillonite and illite dehydrate more slowly, and the loss of OH water is often only complete after firing up to 900 °C. The absence of any calcium aluminosilicate phases indicates a temperature of 850 °C as the upper limit in the estimated range for the firing temperatures. Based on the analytical results, it is preferable to suggest a firing temperature in the range of 600–850 °C. The presence or absence of any sintering or vitrification in the SEM micrographs could be greater than 750 °C [28]. This may be noncalcareous clay and supports above studies. Manitatis et al. [5,29] have studied the effect of calcium content on iron oxide transformation in fired clay. They have reported that, firing at 700 °C results in the appearance of magnetic components either poorly crystallized or substituted hematite. The transformation that takes place which affect the production of iron oxides are the hydroxides present, if any get transformed to Fe2O3 and at 400 °C dehydroxylation of the clay mineral takes place. The associated firing temperature may thus be estimated around 750 °C and this finding is good agreement with FT-IR, PXRD and TG-DTA analysis.

ED-XRF results Table 3 lists the major, minor and trace elements found in the potsherds. Abundant amount of Si, Al, Ca, Fe, K and Ti was found. La, Cu, Zn, Pb, La, Co, V, Cd and Cr were found to be minor constituents. The typical ED-XRF spectrum is shown Fig. 7.

Table 3 Elemental composition of Veeranam potsherds using ED-XRF technique (elements in ppm unless% is indicated). Sample ID/element

TP1

TP2

TP3

TP4

TP5

TP6

Sio2 Al2O3 CaO Fe2O3 K2O TiO2 Cu Zn Pb La Co V Cd Cr

35.96 12.89 2.07 7.32 0.80 0.65 73.7 97.8 25.7 33.7 25.6 142.3 0.3 110.6

41.84 14.30 2.31 7.42 0.90 0.73 71.8 110 18.2 34.8 25.7 138.8 0.3 112.5

23.38 7.94 1.90 5.63 0.52 0.52 74.3 109.7 24.4 39.7 18.6 78.2 0.1 122.5

26.98 8.69 2.04 6.41 0.81 0.62 72.6 138.7 23.6 45 21.4 69.9 0.3 115.4

31.81 11.77 2.42 6.59 0.75 0.68 71.45 100 27.5 46.9 21.7 91.6 0.2 97.2

33.65 11.87 2.43 6.41 0.71 0.72 55.5 115.1 18.8 55.4 21 81.8 0.2 104.7

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851

Fig. 7. Typical ED-XRF spectrum of Veeranam pottery samples.

0.50

Group-C

Linkage Distance

0.45 0.40 0.35

Group-B

0.30 0.25

Group-A 0.20 0.15 TP3

TP6

TP5

TP4

TP2

TP1

Fig. 8. Grouping of Veeranam Potsherds by cluster analysis.

From Table 3, it is obvious that, the concentration of silica is more due to the presence of various amounts of quartz in all the samples of interest. A part from silica, the most abundant impurity elements are Al, Ca, Fe, K and Ti. The potassium content is related to feldspar content. The presence of potassium and Calcium indicates that the alkali may act as fluxes during firing, promoting sintering and viritification [30,31]. The composition of Fe and Ca determines the nature of clay minerals and firing atmosphere adopted by the artisans. The chemical composition can be used to define the pottery of a particular area and people by determining the raw materials used. To know the type of clay minerals (calcareous/non-calcareous and either low or high refractory) and to determine the firing atmosphere adopted by the artisans at the time of manufacture, the chemical analysis was performed on the samples. The clays mainly have the concentrations of silica, (SiO2), alumina (Al2O3) and fluxes (K2O, Fe2O3, CaO, MgO and TiO2) as the composition. The nature of clay minerals whether calcareous or non-calcareous clay can be identified from the percentage of calcium oxide (CaO). According to Maniatis and Tite [5] the clays containing CaO greater than 6%, are known as Calcareous clays and CaO less than 6% are known as non-calcareous clays. This results is very correled with findings of FT-IR and XRD studies and it supports the type of the clay is non-calcareous. If the fluxes concentration (K2O, Fe2O3, CaO, MgO and TiO2) are more than 9% the clays are classified as low refractory and classified as high refractory if the fluxes in the sample are less than 9%.

Based on the above statement, the CaO is less than 6% in our samples show that non-calcareous and also the fluxes concentration are greater than 9% indicates that the clays are low refractory in nature. Cu contents vary between 55.5 and 74.3 ppm and Zinc (Zn) concentrations range from 97.8 to 115.1 ppm respectively. Trace elements like Co, Cr, and V could be used as geochemical fingerprints’ as they are associated to specific petrological types [32]. The concentration of La and Pb is similar for almost all samples. Chromium concentrations range between 97.2 and 122.5 ppm. The quite uniform chemical profile implies in some samples shows that pottery was probably produced locally. It should be noted, however, that the pottery composition depends both in the clay source and in the recipe used to prepare the clay paste [22]. The variation of chemical composition of potsherds may imply pottery from different production sites or reflect the natural in homogeneity of local clay deposits and the application of different manufacture processes in local workshops. The ED-XRF analysis results support the findings of vibrational spectroscopic studies [33]. Statistical analysis Elemental compositions obtained from EDXRF measurements were submitted to Principal Component Analysis (PCA) and hierarchical cluster analysis in order to identify grouping and structure in the data. The samples were analyzed by using STATISTICA

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Hierarchical Cluster Analysis (HCA) The resulting dendrogram is shown in Fig. 8. It was found using single linkage as grouping rule, according to Euclidean distance. It is clear that there are three main Groups. Group-A contains 2 samples (90.13% of the observations). Since Group-A consists of high concentration of major and some minor elements such as Co and V. So they made from same group of clays. Group-B contains 3 samples. Since they have same concentration of elements (Cu) while Group-C contains the very less concentration of Zn. Hence Group-B and Group-C potteries made from slightly different composition clays.

Table 4 Factor loading for fourteen elements in the data set for principal component as factor analysis and Varimax as rotation of potsherds from Veeranam. Variables

Factor-1

Factor-2

Factor-3

SiO2 Al2O3 CaO Fe2O3 K2O TiO2 Cu Zn Pb La Co V Cd Cr

0.9216 0.8593 0.3805 0.9869 0.8998 0.7459 0.0785 0.2168 0.3562 0.5064 0.9845 0.8359 0.8592 0.2285

0.3216 0.3988 0.8988 0.0466 0.1519 0.6580 0.8282 0.1002 0.3020 0.7757 0.0757 0.1750 0.0271 0.8136

0.1140 0.2761 0.0683 0.1169 0.2333 0.0745 0.3157 0.9440 0.5844 0.3215 0.1267 0.4451 0.2875 0.3680

Variance explained by factors%

53.50

23.80

12.83

Principal Component Analysis (PCA) The principal component analysis was used as a tool to examine graphically the grouping pattern of the samples in terms of chemical composition, i.e. to see if there were partitions in terms of pottery type. The first two components, which describe most of the total variance in the elemental variables, usually best separate the different groups of samples; they were often used for the study of the provenance of artefacts [34]. Table 4 shows the factor loading for the three extracted factors. As listed in Table 4, factor 1 explains 53.50% of the total

(version10.0) software package for windows. It is indispensable to employ multivariate statistics that use the correlation between element concentrations as well as the absolute concentrations themselves to characterize different types and sources of pottery. 1.0

caO La

0.8

A

Tio2

0.6 Al203 Sio2

Factor 2

0.4

C

0.2

K2O Fe2O3

Cd

0.0

Co

Zn V

-0.2

Pb

-0.4

B

-0.6 Cr

-0.8 -1.0 -0.6

-0.4

-0.2

Cu

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Factor 1 Fig. 9. Factor score 1 versus factor score 2 of pottery samples of Veeranam.

0.8 Pb

0.6

A V

B

0.4

Cu

Al203

C

0.2

Co Fe2O3 Sio2

Factor 3

caO

0.0

Tio2

-0.2

K2O Cd

La

Cr

-0.4 -0.6 -0.8 Zn

-1.0 -1.2 -0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Factor 1 Fig. 10. Factor score 1 versus factor score 3 of pottery samples of Veeranam.

1.2

R. Ravisankar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 115 (2013) 845–853

variance of the data set, factor 2 explains 23.80% and finally factor 3 explains 12.83%. It is clear that the three factors extracted in this study explain 90.13% of the total variance of the data set. It is clear from Table 4 that the communalities for 90% of the elements are greater than 50%. Therefore, the FA fit to the data set is good [35]. In addition to factor loading, this analysis yields factor scores, which quantify the relative intensities of factor strength on each sample. Factor scores are very helpful in interpreting and understanding factor analysis results and can be helpful in finding errors that may exist in the data set. In addition, factor scores may be utilized to identify grouping of the samples into particular categories samples with the same factor score patterns can be grouped together into these categories. Figs. 9 and 10 present plots of factor score 1 against factor scores 2 and 3, respectively for each of the 10 samples. A deep examination of Figs. 9 and 10 indicates three groups are identified i.e. Group-A, Group-B and Group-C which is also confirmed in cluster analysis shown in Fig. 8. Group-A formed due to high concentration of major element oxides and some minor elements such as Co and V [36]. Group-B due to high content Cu while Group-C having high content of Zn. The results obtained by factor scores confirm that 100% of the pottery samples classified by cluster analysis are correctly classified. The results confirm the existence of one major group in addition to a two small groups.

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Conclusion The application of FTIR, XRD, DTA-TG, microanalysis (SEM-EDX) and EDXRF of the techniques allowed the characterization of potsherds of megalithic sarcophagi. The mineralogical and chemical compositions of the shreds appear to reflect the provenance and potteries groups. The mineralogy of the shred contains quartz, trace amounts of feldspars and iron oxide. The mineralogical composition indicates low temperature firing of the clay. Clays, which were used to make the shreds, are typically referred to as hydrous silicates. When heated above 500 °C, the hydroxyl component is driven off. This results in mica-like structures. If the clays are heated to approximately 900 °C or higher, the clays become vitreous and form porcelain. Thus the shreds in this study probably fired above 500 °C but below 900 °C. We are assuming that prehistoric peoples collected the raw materials around the area, close to the sites. The firing of the potteries in open atmosphere, as demonstrated by partial dehydroxylation of clay material in the samples. Multivariate statistical analysis of ED-XRF data points to two compositional groups, in fair agreement with archaeological classification.

853

[23] [24] [25] [26] [27] [28] [29] [30]

[31] [32] [33] [34] [35] [36]

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