Application of various spectroscopic techniques to characterize the archaeological pottery excavated from Manaveli, Puducherry, India

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Application of various spectroscopic techniques to characterize the archaeological pottery excavated from Manaveli, Puducherry, India G. Raja Annamalai a,∗ , R. Ravisankar b , A. Naseerutheen c , A. Chandrasekaran d , K. Rajan e a

Department of Physics, Shri Krishnaa College of Engineering & Technology, Mannadipet 605501, Puducherry, India Post Graduate and Research Department of Physics, Government Arts College, Thiruvannamalai 606603, Tamilnadu, India Department of Physics, C. Abdul Hakeem College, Melvisharam 632509, Tamilnadu, India d Department of Physics, Vel Tech (Owned by RS Trust), Chennai 600062, Tamilnadu, India e Department of History, School of Social Sciences & International Studies, Pondicherry University, Kalapet, Puducherry, India b c

a r t i c l e

i n f o

Article history: Received 28 October 2013 Accepted 2 June 2014 Available online xxx Keywords: Archaeological samples Firing temperature FT-IR XRD DSC–TGA

a b s t r a c t This paper is focused on a spectroscopic study of some ancient pottery shreds from an archaeological site Manaveli village, Puducherry, India. Analytical characterization using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and differential scanning colorimetric coupled with thermo gravimetric analysis were carried out on red and black ware and red ware recently excavated from the above site. The experimental results of FT-IR and XRD are similar and allowed us to identify the mineralogical composition of pottery samples. In addition, TGA was applied in order to study the dehydration of hydroscopic water and decomposition of carboxyl group in the powdered pottery samples during heating. Moreover, this paper proves that all the above spectroscopic techniques are very useful analytical tool for the examination of ancient pottery, which is also suitable for the identification of its firing temperature and firing atmosphere. © 2014 Elsevier GmbH. All rights reserved.

1. Introduction The most abundant materials found at archaeological sites are potteries, valuable source of information for the study of ancient civilizations in terms of their culture, technological knowledge and ancient trade patterns. The application of analytical techniques to characterize the ancient pottery has proved to be valuable information to the archaeological investigations, aiming to reconstruct the ceramic life cycle, i.e. to extract provenance information and rediscover manufacture technology and use [1]. Manufacturing process of potsherds 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, firing condition and temperature to obtain the finished item. The firing temperature of ancient pottery is normally estimated by investigating mineral phases or determining experimental parameters which are temperature-dependent [2]. From long list of instrumental techniques such as Fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), thermo gravimetric analysis (TGA) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy

∗ Corresponding author. Tel.: +91 9786317621. E-mail address: [email protected] (G.R. Annamalai).

(SEM-EDX), may successfully answer the above issues [3–8]. Clay materials are usually analysed by the use of techniques such as Xray fluorescence and X-ray diffraction in which case it is difficult to identify poorly crystallized kaolinite. Infrared spectroscopy is however becoming an important tool for such qualitative identification. The application of the IR spectroscopy greatly increased in many spheres of clay research by the introduction of Fourier transform instrumentation. Thermal studies of clay minerals using TG and DTA were mainly confined to the monitoring of the dehydration processes because shreds have been buried and easily exposed to absorbed water. The present work focuses on the results of various spectroscopic study of pottery recently excavated from the archaeological site at Manaveli, Puducherry, India. The mineralogy and firing of temperature of the archaeological bodies were examined by FT-IR and XRD. TGA is the complementary technique used to examine the firing temperature from the thermal characteristic reactions. 2. Materials and methods 2.1. Sample collection Manaveli is one of the archaeological sites in Puducherry, India, near the archaeological site of Arikamedu on the outskirts of Puducherry town. The pottery samples were excavated

http://dx.doi.org/10.1016/j.ijleo.2014.06.099 0030-4026/© 2014 Elsevier GmbH. All rights reserved.

Please cite this article in press as: G.R. Annamalai, et al., Application of various spectroscopic techniques to characterize the archaeological pottery excavated from Manaveli, Puducherry, India, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.099

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Fig. 1. Photograph of Manaveli pottery samples. Fig. 2. FT-IR spectra of Manaveli potttery samples.

(11◦ 53 26 N;

79◦ 48 32 E)

from Manaveli of Union Territory of Puducherry, India, by the Department of History, University of Pondicherry, Puducherry, India. The pottery shreds of Manaveli belong to the 5th century BC. Black and Redware, Red ware were collected in this site. The visual photograph of the collected pottery samples are shown in Fig. 1 The samples are designated as MP1, MP2, & MP3. After removal of an area of commercial clay extraction at a depth 30 cm to avoid the layer of surface vegetation, the pottery shreds were grounded into fine powder using agate mortar. 2.2. FT-IR technique FT-IR spectra on the pottery samples were recorded on a Bruker Alpha FT-IR spectrometer available in department of chemistry, Government Arts College, Tiruvannamalai, Tamilnadu, India, using KBr pellets technique in the wave number range from 4000 cm−1 to 400 cm−1 . The KBr pressed pellet technique was used by mixing the powdered samples with KBr in weight proportion of 1:20. The spectra were recorded in the mid region of 4000–400 cm−1 in the received state. The precision of the instrument is ±5 cm−1 . 2.3. XRD analysis Powder X-ray diffraction data of the powdered pottery samples was carried out on a Siemens D500Advance diffractometer using Cu K␣ radiation, equipped with a NaI(Tl) scintillation detector. The Xray patterns of powdered pottery samples were recorded at room temperature. Diffraction data over a 2 range of 10 to 70◦ were recorded by using diffractometer. Mineralogical composition of the studied samples is determined with the standard interpretation procedures of XRD. 2.4. Thermo gravimetric analysis (DSC–TGA) As the thermo gravimetric analysis has gained wide analytical acceptance in recent years for compositional analysis, DSC–TGA study was carried out for the samples in SDT Q-600-V.8.0 thermal analyzer. The experiment was carried out by heating the samples from 30 to 1000 ◦ C at 10 ◦ C min−1 with flow of high purity nitrogen. 3. Results and discussions 3.1. FT-IR mineral analysis The FT-IR spectra (4000–400 cm−1 ) of the red, red and black pottery fragments of Manaveli are given in Fig. 2 The identified

minerals by IR characteristics are shown in Table 1 In all the spectra, quartz is dominated phase with bands at 780, 700 and 460 cm−1 . The presence of the sharp band at 695 cm−1 indicates thin particles and in the case of thick particles, this band has shifted to 689 cm−1 . Since the spectrum of the clay sample shows this band at 687 cm−1 it is clear that this clay contains quartz of thick particle size [3]. The weak band observed at 2926 cm−1 (␯CH) is along with the weak band at 2853 cm−1 , probably originated from organic residues [9]. The band around at 1030 cm−1 is assigned to Si O stretching mode of silicates/clays. The SiO deformation band of the clays appears at 467 cm−1 . The clay minerals such as kaolinite and montomorilinte were identified by the presence of the peak at 1030, 1635 & 3440 cm−1 , respectively. The presence of bands 427, 591 and 1050 cm−1 are due to microcline, orthoclase at 465, 645 & 730 cm−1 and albite 725 cm−1 indicate feldspar group of minerals in the samples. The presence of absorption bands around 580 and 540& 476 cm–1 are due to magnetite and hematite, respectively, stated by Velraj et al. [10]. The weak band at 3445 cm−1 is along with 1645 cm−1 due to OH stretching of hydroscopic water. The spectroscopic results indicate that black colouration was due to concentrations of magnetite, red colouration due to concentration of hematite. The presence of haematite also indicates firing in the oxidising atmosphere [4]. The amount of the organic contribution is higher in red part in comparison with the black decoration part [11]. No calcite bands were observed in all the spectra of the samples which indication of non-calcareous clay type. FT-IR spectroscopic results reveal that the presence of minerals quartz, feldspars (microcline, orthoclase and albite), clay minerals (kaolinite and montormorlinite), iron oxides (hematite and magnetite) and organic compounds. The assignment has been made on the basis of the characteristic IR wave numbers of the minerals [12,13]. The analysis results of all the three archaeological materials are similar. 3.2. FT-IR firing temperature analysis The absence of firing minerals namely, the IR absorption bands of plagioclase-anorthite, pyroxene-diopside, melilite-gehlenite and wollastonite in the archaeological body clearly indicate the low firing temperature. On the other hand, microcline (K-feldspar) is known to be stable up to a temperature ranges 500–750 ◦ C [12]. The decomposition of kaolinite and formation of metakaolinite occurs in the temperature range 500–650 ◦ C [3,14]. The appearance of kaolinite in all the samples reveals that the firing temperature was not high enough to complete the decomposition of this mineral indicating that the fi ring did not exceed 650 ◦ C. The band at

Table 1 The observed absorption wave numbers and corresponding minerals from FTIR spectra of Manaveli pottery samples. S. No.

Sample ID

Quartz

Feldspars

Clay minerals

Iron oxides

Organic carbon

1 2 3

MP1 MP2 MP3

776, 460 776, 701, 460 777, 687, 458

723, 641, 588, 427 728, 641, 590 1049, 646,590

1031, 3441, 1637 1032, 3443, 1638 1029, 1645, 3439

579, 538, 476 539 538

2926, 2854 2920, 2853 2926, 2849

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Fig. 3. XRD pattern of Manaveli pottery sample.

915 cm−1 is due to Al(OH) vibrations in the octahedral sheet structure which begins to disappear with increasing temperature and at 500 ◦ C the band collapses completely and a broad symmetry band is observed in all the samples around at 1030 cm−1 for red clay [4,15]. None of the samples in the spectra indicates for the present study showed the sharp shoulder band at 915 cm−1 . The presence of kaolinite and the absence of Al (OH) vibrations in the spectra of all samples of Manaveli show that firing temperature lies between 500 and 650 ◦ C. From the above discussions one can conclude that the samples were subjected to firing temperature greater than 500 ◦ C under oxidizing atmospheric condition and the type of the clay used is red clay. 3.3. XRD analysis Clay samples from different sources can consist of different components and the ratio of various constituents also differs from clay to clay. The discrepancies in clay composition can be easily and reliably detected by X-ray diffraction analysis. The different pottery fragments of Manaveli, analysed by XRD non-destructive technique. The XRD spectrum of selected sample of Manaveli potsherds is shown in Fig. 3. Qualitative mineralogy of the studied samples is determined with the standard interpretation procedures of XRD [16]. In the samples the presence of major quartz, minor feldspar as well as the presence of iron oxides was detected. Red paint in the samples is clearly characterized by hematite. However the identification of the original colouring minerals is difficult to be performed in the fired pigments. In fact, as clearly evidenced by Mastrotheodoros et al. [17], most of the iron oxides used in antiquity for producing pigments change their mineralogical phase to hematite during firing. In fact oxides maintain a red colour when they are fired mixed with clays below 900 ◦ C. Above 500 ◦ C iron component formed and it was attributed to iron oxides in the oxidising atmosphere. The XRD analysis of the red and black pigments showed the presence of both hematite and magnetite. Finally, very rich in quartz, and the secondary phases are composed by albite and orthoclase and a minor phase of hematite (Fe2 O3 ) analysed in the samples. XRD study also reveals that the pottery samples were fired above 500 ◦ C during manufacturing by ancient potter. The XRD results are in good agreement with the FT-IR results. 3.4. Thermal analysis DSC and TGA curve of the selected pottery sample of Manaveli is shown in Fig. 4 Thermal analyses were carried out at heating 10 ◦ C min−1 from 30 ◦ C to 1000 ◦ C. The endothermic peak around 100 to 200 ◦ C is due to the moisture water [18]. No endothermic peaks were observed in this temperature range which indicates that absence of hydroscopic water. The exothermic peak in the range of 200–450 ◦ C is due to the combustion of organic material [19]. This peak was present in the sample MP1 at 368 ◦ C indicating the pottery only has organic material in it and weight loss in this

Fig. 4. DSC–TGA curves of Manaveli pottery sample.

region is 6.664%. This is higher weight loss observed in the sample throughout the experiment, this weight loss due to combustion of organic materials only. The organic material might be added intestinally as a binder in the manufacturing of pottery or the raw material itself contained organic material [18]. The endothermic peak at 500 to 650 ◦ C is due to the dehydroxylation of kaolinite [20]. In MP1 the presence of kaolinite is well evidenced by endothermic at around 530 ◦ C. The presence of this peak indicates that the pottery has not been fired above this temperature. Therefore, the shred MP1 would have been fired above 500 ◦ C. The decomposition of calcite occurs in between the temperature 700–800 ◦ C [21]. No weight loss was observed in this temperature range regarding calcite. The absence of calcite in thermo gravimetric analysis is the good evidence between 700 and 800 ◦ C which supports the results of the XRD and FTIR analysis done in the present study. The total weight loss throughout the analysis is 11.10%. The DSC–TGA results are in good agreement with the FT-IR and XRD results. 4. Conclusion FT-IR spectroscopy was applied for the mineralogical and firing temperature investigation of the pottery excavated from the site Manaveli, Puducherry, India. The investigated archaeological samples consisted of five distinct groups of minerals such as silicate mineral quartz, feldspar, clay minerals, iron oxides and organic compounds, the baking temperature of the fragments also were found as above 500 ◦ C. The investigation of FT-IR study was also confirmed by XRD data. The results of FT-IR technique well coincide with XRD. Thermal characterization of pottery samples such as dehydration and dehudroxylation (weight loss during to heating) were studied and it is inferred that the samples were also fired above 500 ◦ C. References [1] M.S. Tite, Ceramic production, provenance and use e a review, Archaeometry 50 (2008) 216–231. [2] M. Maggetti, Phase analysis and its significance for technology and origin, in: J.S. Olin, A.D. Franklin (Eds.), Archaeological Ceramics, Smithsonian Institution Press, Washington, 1982, pp. 121–133. [3] R. Ravisankar, G. RajaAnnamalai, A. Naseerutheen, A. Chandrasekaran, M.V.R. Prasad, K.K. Satpathy, C. Maheswaran, Analytical characterization of recently excavated megalithic sarcophagi potsherds in Veeranam village, Tiruvannamalai dist., Tamilnadu, India, Spectrochim. Acta, A: Mol. Biomol. Spectrosc. 115 (2013) 845–853. [4] R. Ravisankar, S. Kiruba, C. Shamira, A. Naseerutheen, P.D. Balaji, M. Seran, Spectroscopic techniques applied to the characterization of recently excavated ancientpotteries from Thiruverkadu, Tamilnadu, India Microchem. J. 99 (2011) 370–375. [5] L. Paama, I. Pitkanen, P. Peramaki, Analysis of archaeological samples and local clays using ICP-AES, TG-DTG and FTIR techniques, Talanta 51 (2000) 349–357.

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