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Estimation of firing temperature of some archaeological pottery shreds excavated recently in Tamilnadu, India
Spectrochimica Acta Part A 72 (2009) 730–733
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Estimation of firing temperature of some archaeological pottery shreds excavated recently in Tamilnadu, India G. Velraj a,∗ , K. Janaki a , A. Mohamed Musthafa a , R. Palanivel b a b
Department of Physics, Periyar University, Salem 636011, Tamilnadu, India Department of Physics, Annamalai University, Annamalai nagar 608002, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 18 December 2007 Received in revised form 5 August 2008 Accepted 15 November 2008 Keywords: FT-IR SEM Firing temperature Vitrification Pottery shreds
a b s t r a c t An attempt has been made in the present work to estimate the firing temperature of the archaeological pottery shreds excavated from the three archaeological sites namely Maligaimedu, Thiruverkadu and Palur in the state of Tamilnadu in INDIA. The lower limit of firing temperature of the Archaeological pottery shreds were estimated by refiring the samples to different temperatures and recording the corresponding FT-IR spectrum. The firing methods and conditions of firing were inferred from the characteristic absorption positions and the bands observed due to the presence of magnetite and hematite in the samples. In addition, the Scanning Electron Microscopic analysis were carried out to study the internal morphology, vitrification factor and the upper limit of the firing temperature of the potteries fired at the time of manufacture. © 2008 Elsevier B.V. All rights reserved.
1. Introduction The physical characteristics of the potteries like the colour, texture, style and size of the clay particles composing them can reveal the civilization, technology of manufacture and method of firing adopted to bake them and the technical skill evolved by the ancient artisans lived at that time. The estimation of the firing temperature of the potteries used by them throws light to identify the purposes for which they had used them in the daily routines of their living at that time [1,2]. In the production of pottery the firing and consequent cooling are the two important and most crucial stages. From the knowledge of firing temperature value achieved and method of firing one may be able to conclude how the process navigated and tempered the raw clay used to model a vessel. To estimate the firing temperature and the limit of temperature of the archaeological artifacts, different physic-chemical methods have been evolved in the study of chemical compositions of the potteries. In the study of ancient pottery it is important to combine geological, laboratory and technological techniques to achieve good results. One technique is usually not enough to characterize and define the mineralogy and firing temperatures because shreds have been buried and easily exposed to extensive weathering process [3]. Hence FT-IR and SEM are the two techniques employed in the present work to estimate the firing temperatures achieved by the artisans of ancient times and the firing techniques adopted for the
∗ Corresponding author. Tel.: +91 427 2345766; fax: +91 427 2345124. E-mail address: [email protected] (G. Velraj). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.11.015
pottery shreds collected at different depths from the three sites of archeological interest in Tamilnadu.
2. Materials and methods The pottery shreds from Maligaimedu, Thiruverkadu and Palur were examined using FT-IR and SEM with a view to acquire information on the techniques employed on the samples to fire them and to estimate the limits of firing temperatures. The samples from the three sites of interest are named as MM1, MM4, MM6 of Maligaimedu and TK1, TK4, TK6 of Thiruverkadu and PL1, PL5, PL6 of Palur.
2.1. Fourier transform infrared spectroscopy (FT-IR) The coloured samples were subjected to refiring at different temperatures around 200, 400, 600 and 800 ◦ C for one hour using muffle furnace. The spectra were recorded in the explored range of frequencies 4000–400 cm−1 for the refired samples after cooling to room temperature using Nicolet Avatar FT-IR spectrometer. The samples were pelletized by mixing with the spectra grade KBr at the ratio of 1:20 by weight [4]. The KBr pellet of 13 mm diameter was kept inside the sample holder and scanned at 1 cm−1 resolution for the entire mid-infrared region till the identical charts were obtained in the consecutive trials. The extinction coefficient for the magnetite and hematite bands was determined using the method by Venkatachalapathy et al. [5].
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Fig. 1. FT-IR spectra of the sample MM4. Fig. 3. FT-IR spectra of the sample PL1.
2.2. Scanning Electron Microscope (SEM) The microphotographs of the sample were recorded using SEM JSM 561OLV JEOL. The maximum magnification possible in the equipment is 3,00,000 times with the resolution of 3 nm.The elemental analysis were done using the OXFORD INCA Energy Dispersive X-ray Fluorescence spectrometer (EDS). The fresh fracture surfaces of the potteries in the received state (ARS) that were coated with the thin layer of platinum were examined using SEM, typically setting at a magnification of ×2000 for all the sample of study. The microphotographs were recorded with the attached accessories of high-resolution cathode ray tube and a role film camera.
up to 800 ◦ C. From the FT-IR spectra of the samples taken for the present study one can infer that the samples MM4 (Fig. 1) and MM6 showed the absorption around 3626 and 3627 cm−1 respectively which indicates that both the samples may be fired below 800 ◦ C and the samples MM1, TK1 (Fig. 2), TK4, TK6, PL1 (Fig. 3), PL5 and PL6 do not show any absorption band at 3630 cm−1 in the received state itself indicating that these samples would have been fired to temperature 800 ◦ C or above. The above result can also be confirmed with the bands at 915 and 875 cm−1 . The band at 915 cm−1 is due to Al(OH) vibrations in the
3. Results and discussion In the map of India, Tamilnadu is known for its cultural heritage and civilization over the past 1400 years. The archaeological excavation sites where the pottery artifacts collected are Maligaimedu, Thiruverkadu and Palur in Tamilnadu. Maligaimedu is the location identified by the State Department of Archaeology, Government of Tamilnadu and the other two sites Thiruverkadu and Palur in Tamilnadu are the identified Archaeological sites by the Department of Ancient History and Archaeology, University of Madras, Tamilnadu. The FT-IR spectra and SEM photographs of some specific samples are given in Figs. 1–3 and Plates 1–3. Their firing temperature limits were reported in Tables 1 and 2 with the locations cited in the title of the table respectively. According to Mendelovici et al. [6] the absorption band around 3630 cm−1 is due to crystalline hydroxyl groups which persist only
Plate 1. Microphotograph of the sample MM4.
Fig. 2. FT-IR spectra of the sample TK1.
Plate 2. Microphotograph of the sample TK1.
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G. Velraj et al. / Spectrochimica Acta Part A 72 (2009) 730–733
Table 1 Estimated firing temperature of the pottery shreds excavated at Maligaimedu, Thiruverkadu and Palur. Sample
Colour
Atmosphere prevailed
Dehydroxylation of hydroxyl band
Octahedral sheet structure
Estimated firing temperature (◦ C)
MM1 MM4 MM6 TK1 TK4 TK6 PL1 PL5 PL6
Red slipped ware Red slipped ware Red ware Red slipped ware Red ware Black ware Red ware Red slipped ware Black &Red ware
Oxidizing Oxidizing Reducing Oxidizing Oxidizing Oxidizing Oxidizing Oxidizing Reducing
Completed Incomplete Incomplete Completed Completed Completed Completed Completed Completed
Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared
>800 ◦ C <800 ◦ C <800 ◦ C >800 ◦ C >800 ◦ C >800 ◦ C >800 ◦ C >800 ◦ C >800 ◦ C
Table 2 Vitrification stage and firing temperature of the archaeological potteries of Maligaimedu, Thiruverkadu and Palur. Sample
Colour
Atmosphere
Clay type
Virtification stage
MM1 MM4 MM6 TK1 TK4 TK6 PL1 PL5 PL6
Red slipped ware Red slipped ware Red ware Red slipped ware Red ware Black ware Red ware Red slipped ware Black and Red ware
Oxidizing Oxidizing Reducing Oxidizing Oxidizing Oxidizing Oxidizing Oxidizing Reducing
NC NC NC NC NC C NC NC NC
IV NV IV CV IV IV EV IV EV
Firing temperature ranges (◦ C) 800–850 <800 750–800 850–950 800–850 800–850 850–950 800–850 800–900
NC: Non-Calcareous; IV: Initial Vitrification; CV: Continuous Vitrification; C: Calcareous; NC: No Vitrification; EV: Extensive Vitrification.
octahedral sheet structure which begins to disappear with increasing temperature and at 500 ◦ C the band disappears completely [1,7]. None of the samples taken for the present study showed the sharp shoulder band at 915 cm−1 . This implies that all the samples were fired to the temperature above 500 ◦ C. According to Yariv and Mendelovici [8] a shoulder band at 875 cm−1 indicates dehydroxylation of Kaolinite minerals which are completed at 800 ◦ C and octahedral sheet structure in the clay mineral disappeared. This again reaffirms that one of the samples from Maligaimedu named as MM1 and all the other remaining Thiruverkadu and Palur samples were fired to a temperature above 800 ◦ C. But the shoulder band does not appear in the Maligaimedu samples MM4 and MM6 because iron content in the samples may be less in quantity and may be fired below 800 ◦ C. The broad absorption bands at 580 and 540 cm−1 have been attributed to Magnetite and Hematite respectively [8–11]. The amount of Magnetite and Hematite decides the reducing or oxidizing atmosphere for firing the artifacts [10,12–14]. The method of firing is very important rather than temperature numbers, as temperature in general is extremely unstable and variable through time and space, within a structure and even on a single
Plate 3. Microphotograph of the sample PL1.
vessel [15,16]. The FT-IR spectra of the samples MM4, TK1 and PL1 show absorption due to hematite indicating that these samples were fired in the open air or perfectly oxidizing atmosphere at the time of manufacture. The less amount of magnetite is due to the transformation of Fe3 O4 to Fe2 O3 during the process of firing [17]. The presence of carbonaceous materials present in the Maligaimedu samples MM1 and MM4 were identified from the infrared vibrational analysis of the spectra of the samples. So charcoal and wood might have been used to fire these samples at the time of manufacture by the ancient artisans belonging to 13th and 14th century AD at Maligaimedu. The pottery shreds TK4 and TK6 show no absorption due to magnetite and hematite because of their low abundance in the samples. The absorption at 535 cm−1 appeared for these samples refired to temperature of 200 ◦ C indicates that these samples were fired in the oxidizing atmosphere. So the artisans of Thiruverkadu were aware of the open air or oxidizing atmosphere technique for firing the potteries made out of the clay materials. The presence of iron, either in pure state or in the form of oxides is the key factor to understand the colour of the potteries. The colour of the pottery is due to the content of iron oxides which acts as the colouring agent. Yariv and Mendelovici [8], Mirti et al. [12,18], and Piero Mirti and Patrizia Davit [13] observed that the colour of the potteries is due to hematite which is a red brown solid and decides the atmospheric conditions (oxidizing/reducing) where the artifacts were fired. The potteries collected from Maligaimedu namely MM1 and MM4, Thiruverkadu potteries TK1, TK4 and Palur samples PL1, PL5 were Red Slipped/Red ware in colour and shows the presence of hematite and hence fired in the oxidizing atmosphere. The black and red coloured potteries PL6 and MM6 probably fired in the reducing atmosphere. This may be due to the air blow into the kiln at the time of firing. Maniatis and Tite [19,20,22], Tite et al. [21], Maniatis et al. [23], Maniatis [24] and Noll et al. [25] have studied the ancient pottery shreds using SEM on similar lines and the development of the vitrification. The approximate firing temperature ranges associated with the various vitrification stages observed in the non-calcareous clays are given by them. The SEM Micro photographs of the samples of interest are shown in Plates 1–3. The pottery shreds MM1, TK4 and PL5 indicate the presence of glassy minerals along with the region of glass areas. This pattern is similar to the one expected
G. Velraj et al. / Spectrochimica Acta Part A 72 (2009) 730–733
out of a clay material of initial vitrification of low refractory, noncalcareous clay type subjected to a firing temperature 800–850 ◦ C [26]. It is understood from the FT-IR studies for the same samples that the atmosphere prevailed at the time of manufacturing is the oxidizing condition and the lower limit of the firing temperature is greater than 800 ◦ C. As shown in Plate 1, the sample MM4 shows no vitrification. Maniatis and Tite [20] have stated that non-calcareous clays fired at temperatures below 800 ◦ C will produce no vitrification. The pottery shreds of low refractory, non-calcareous clay fired in the oxidizing condition was subjected to the firing temperature below 800 ◦ C. The incomplete dehydroxylation exhibited by the pottery shred MM4 in the FT-IR study confirm that the firing temperature value for this pottery shreds is below 800 ◦ C. The pottery shred MM6 was in initial vitrification stage because the glassy fibrous region is along with the region of glass areas. Maniatis and Tite [20] have stated that the low refractory non-calcareous clays show initial vitrification, if they were fired in the temperature range 750–800 ◦ C. The FT-IR studies of this sample also revealed that it was fired below 800 ◦ C under reduced atmosphere. The SEM analysis helped to narrow down the ranges of firing temperature in the interval 750–800 ◦ C. Besides it is in agreement with the FT-IR studies to fix the lower limit of the firing temperature. The pattern and the behavior of the sample TK1 (Plate 2) is similar to the one described by Maniatis et al. [23] for the archaeological potteries. The clay was in continuous vitrification stage of non-calcareous type and fired in the oxidizing atmosphere in the temperature range 850–950 ◦ C. The sample TK6 is of low refractory calcareous type and was in initial vitrification stage and fired in the temperature range 800–850 ◦ C in the oxidizing atmosphere in accordance with the reports of Maniatis [24]. The sample PL1 (Plate 3) show extensive vitrification stage and fired in the oxidizing atmosphere in the temperature range 850–950 ◦ C. The sample PL6 has been fired in the reducing atmosphere in the range of 800–900 ◦ C as it is a non-calcareous type and of extensive vitrification stage as reported by Maniatis [24]. The SEM results of the Palur samples PL1, PL4 and PL6 are consistent with the FT-IR results obtained on the same samples. From the study of the colour and firing temperature of the pottery shreds excavated at the three sites, it is clear that the both open air firing and oxidizing atmosphere conditions were used for firing in kilns in reduced atmosphere by the ancient artisans. So the people lived at the time of manufacture of the potteries in the respective areas of the excavations were aware of the technology of perfection to achieve good quality of their products. They might have used clay containing hematite rich composition to produce potteries. The presence of the black and red colour on the pottery samples studied may be attributed to the blow of air in the closed kiln during the process of firing at reduced atmosphere.
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Acknowledgements The authors are grateful to The Director, The State Department of Archaeology, and also the Head of the department of Ancient History and Archaeology, University of Madras, Chennai, Tamil Nadu, for providing the archaeological samples for this research work. The authors also extended their sense of gratitude to the staff-in-charge of CSIL (Centralized Sophisticated Instrumentation Lab) Annamalai University, Annamalainagar for giving permission to access the FTIR and SEM facility to record the spectra and microphotographs of the samples. References [1] K. Ramasamy, M. Kamalakkannan, Indian J. Pure Appl. Phys. 25 (1987) 284–286. [2] H. Van olphen, J.J. Fripat, Data Handbook for Cal Materials and Other NonMetallic Minerals, Ist ed., Pergamon press, London, 1979, p. 285. [3] R. Sivano, Bertolino, Mariano Fabra, Appl. Clay Sci. 24 (2003) 21–34. [4] R. Palanivel, G. Velraj, Indian J. Pure Appl. Phys. 25 (2007) 501–508. [5] R. Venkatachalapathy, C. Manoharan, T. Sridharan, C.M. Basilraj, Indian J. Pure Appl. Phys. 40 (2001) 207–212. [6] E. Mendelovici, S.H. Yariv, Villalba, Clay Miner. 14 (1979) 323–331. [7] J. Hlavay, K. Jonas, S. Elek, J. Inczedy, Clays Clay Miner. 25 (1977) 451–456. [8] S.H. Yariv, E. Mendelovici, Appl. Spectrosc. 33 (4) (1979) 410. [9] H. Kodama, Infrared spectra of minerals, reference guide to identification and characterization of minerals for study of soils, Tech, Bull, 1985-IE, Research branch, Agriculture, Canada, 1985. [10] D. Barilaro, G. Barone, V. Crupi, M.G. Donato, D. Majolino, G. Messina, R. Ponterio, J. Mol. Struct. 744–747 (2005) 827–831. [11] W. Griffith, in: R.J.H. Clark, R.E. Hester (Eds.), Advances in the Raman and Infrared Spectroscopy of Inorganic Based Materials, Wiley, Chichester, 1987, Chapter 2. [12] P. Mirti, A. Perardi, M. Gulmini, Archaeometry 48 (1) (2006) 31–43. [13] Piero Mirti, Patrizia Davit, J. Archaeol. Sci. 31 (2004) 741–751. [14] S. Akyuz, T. Akyuz, S. Basaran, C. Bolacal, A. Gulec, J. Mol. Struct. 834–836 (2007) 150–153. [15] A. Livingstone Smith, J. Archaeol. Sci. 28 (2001) 991–1003. [16] O.P. Gosselain, J. Archaeol. Sci. 19 (1992) 243–259. [17] G.O. Harrell, R.R. Russell, Influence of Ambient Atmosphere in Maturation of structural products, Bulletin 204, Engineering Experiment station, Chio state University, Columbus, 1967. [18] P. Mirti, M. Gulmini, A. Perardi, P. Davit, D. Elia, Anal. Bioanal. Chem. 380 (2004) 712–718. [19] Y. Maniatis, M.S. Tite, Trans. J. Br. Ceram. Soc. 74 (7) (1975) 229–232. [20] Y. Maniatis, M.S. Tite, Ceramic Technology in the Aegan world during the Bronze Age, Thera and Aegan world I London, 1978, p. 483. [21] M.S. Tite, Y. Maniatis, N.D. Meeks, M. Bimson, M.J. Hughes, S.C. Leppard, Technological studies of ancient ceramics, in: T.A. Wertime, S.F. Wertime (Eds.), Early Pyrotechnology, Smithsonian Institution Press, Washington DC, 1982. [22] Y. Maniatis, M.S. Tite, J. Archaeol. Sci. 8 (1981) 59–76. [23] Y. Maniatis, A. Simpoulos, A. Kostikas, V. Perdikatsis, J. Am. Ceram. Soc. 66 (1) (1983) 773. [24] Y. Maniatis, Firing conditions of white - on - dark ware from Easter Crete, East Cretan white on Dark ware Ed. P.P. Betan court, University of Pennsylvania, 1984, p. 75. [25] W. Noll, R. Holm, L. Born, Painting of Ancient Ceramics, Angewandte chemie, International Edition, vol. 14, 1975, pp. 602–619. [26] M.S. Tite, Y. Maniatis, Trans. J. Br. Ceram. Soc. 74 (1) (1975) 19–22.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Estimation of firing temperature of some archaeological pottery shreds excavated recently in Tamilnadu, India G. Velraj a,∗ , K. Janaki a , A. Mohamed Musthafa a , R. Palanivel b a b
Department of Physics, Periyar University, Salem 636011, Tamilnadu, India Department of Physics, Annamalai University, Annamalai nagar 608002, Tamilnadu, India
a r t i c l e
i n f o
Article history: Received 18 December 2007 Received in revised form 5 August 2008 Accepted 15 November 2008 Keywords: FT-IR SEM Firing temperature Vitrification Pottery shreds
a b s t r a c t An attempt has been made in the present work to estimate the firing temperature of the archaeological pottery shreds excavated from the three archaeological sites namely Maligaimedu, Thiruverkadu and Palur in the state of Tamilnadu in INDIA. The lower limit of firing temperature of the Archaeological pottery shreds were estimated by refiring the samples to different temperatures and recording the corresponding FT-IR spectrum. The firing methods and conditions of firing were inferred from the characteristic absorption positions and the bands observed due to the presence of magnetite and hematite in the samples. In addition, the Scanning Electron Microscopic analysis were carried out to study the internal morphology, vitrification factor and the upper limit of the firing temperature of the potteries fired at the time of manufacture. © 2008 Elsevier B.V. All rights reserved.
1. Introduction The physical characteristics of the potteries like the colour, texture, style and size of the clay particles composing them can reveal the civilization, technology of manufacture and method of firing adopted to bake them and the technical skill evolved by the ancient artisans lived at that time. The estimation of the firing temperature of the potteries used by them throws light to identify the purposes for which they had used them in the daily routines of their living at that time [1,2]. In the production of pottery the firing and consequent cooling are the two important and most crucial stages. From the knowledge of firing temperature value achieved and method of firing one may be able to conclude how the process navigated and tempered the raw clay used to model a vessel. To estimate the firing temperature and the limit of temperature of the archaeological artifacts, different physic-chemical methods have been evolved in the study of chemical compositions of the potteries. In the study of ancient pottery it is important to combine geological, laboratory and technological techniques to achieve good results. One technique is usually not enough to characterize and define the mineralogy and firing temperatures because shreds have been buried and easily exposed to extensive weathering process [3]. Hence FT-IR and SEM are the two techniques employed in the present work to estimate the firing temperatures achieved by the artisans of ancient times and the firing techniques adopted for the
∗ Corresponding author. Tel.: +91 427 2345766; fax: +91 427 2345124. E-mail address: [email protected] (G. Velraj). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.11.015
pottery shreds collected at different depths from the three sites of archeological interest in Tamilnadu.
2. Materials and methods The pottery shreds from Maligaimedu, Thiruverkadu and Palur were examined using FT-IR and SEM with a view to acquire information on the techniques employed on the samples to fire them and to estimate the limits of firing temperatures. The samples from the three sites of interest are named as MM1, MM4, MM6 of Maligaimedu and TK1, TK4, TK6 of Thiruverkadu and PL1, PL5, PL6 of Palur.
2.1. Fourier transform infrared spectroscopy (FT-IR) The coloured samples were subjected to refiring at different temperatures around 200, 400, 600 and 800 ◦ C for one hour using muffle furnace. The spectra were recorded in the explored range of frequencies 4000–400 cm−1 for the refired samples after cooling to room temperature using Nicolet Avatar FT-IR spectrometer. The samples were pelletized by mixing with the spectra grade KBr at the ratio of 1:20 by weight [4]. The KBr pellet of 13 mm diameter was kept inside the sample holder and scanned at 1 cm−1 resolution for the entire mid-infrared region till the identical charts were obtained in the consecutive trials. The extinction coefficient for the magnetite and hematite bands was determined using the method by Venkatachalapathy et al. [5].
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Fig. 1. FT-IR spectra of the sample MM4. Fig. 3. FT-IR spectra of the sample PL1.
2.2. Scanning Electron Microscope (SEM) The microphotographs of the sample were recorded using SEM JSM 561OLV JEOL. The maximum magnification possible in the equipment is 3,00,000 times with the resolution of 3 nm.The elemental analysis were done using the OXFORD INCA Energy Dispersive X-ray Fluorescence spectrometer (EDS). The fresh fracture surfaces of the potteries in the received state (ARS) that were coated with the thin layer of platinum were examined using SEM, typically setting at a magnification of ×2000 for all the sample of study. The microphotographs were recorded with the attached accessories of high-resolution cathode ray tube and a role film camera.
up to 800 ◦ C. From the FT-IR spectra of the samples taken for the present study one can infer that the samples MM4 (Fig. 1) and MM6 showed the absorption around 3626 and 3627 cm−1 respectively which indicates that both the samples may be fired below 800 ◦ C and the samples MM1, TK1 (Fig. 2), TK4, TK6, PL1 (Fig. 3), PL5 and PL6 do not show any absorption band at 3630 cm−1 in the received state itself indicating that these samples would have been fired to temperature 800 ◦ C or above. The above result can also be confirmed with the bands at 915 and 875 cm−1 . The band at 915 cm−1 is due to Al(OH) vibrations in the
3. Results and discussion In the map of India, Tamilnadu is known for its cultural heritage and civilization over the past 1400 years. The archaeological excavation sites where the pottery artifacts collected are Maligaimedu, Thiruverkadu and Palur in Tamilnadu. Maligaimedu is the location identified by the State Department of Archaeology, Government of Tamilnadu and the other two sites Thiruverkadu and Palur in Tamilnadu are the identified Archaeological sites by the Department of Ancient History and Archaeology, University of Madras, Tamilnadu. The FT-IR spectra and SEM photographs of some specific samples are given in Figs. 1–3 and Plates 1–3. Their firing temperature limits were reported in Tables 1 and 2 with the locations cited in the title of the table respectively. According to Mendelovici et al. [6] the absorption band around 3630 cm−1 is due to crystalline hydroxyl groups which persist only
Plate 1. Microphotograph of the sample MM4.
Fig. 2. FT-IR spectra of the sample TK1.
Plate 2. Microphotograph of the sample TK1.
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G. Velraj et al. / Spectrochimica Acta Part A 72 (2009) 730–733
Table 1 Estimated firing temperature of the pottery shreds excavated at Maligaimedu, Thiruverkadu and Palur. Sample
Colour
Atmosphere prevailed
Dehydroxylation of hydroxyl band
Octahedral sheet structure
Estimated firing temperature (◦ C)
MM1 MM4 MM6 TK1 TK4 TK6 PL1 PL5 PL6
Red slipped ware Red slipped ware Red ware Red slipped ware Red ware Black ware Red ware Red slipped ware Black &Red ware
Oxidizing Oxidizing Reducing Oxidizing Oxidizing Oxidizing Oxidizing Oxidizing Reducing
Completed Incomplete Incomplete Completed Completed Completed Completed Completed Completed
Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared Disappeared
>800 ◦ C <800 ◦ C <800 ◦ C >800 ◦ C >800 ◦ C >800 ◦ C >800 ◦ C >800 ◦ C >800 ◦ C
Table 2 Vitrification stage and firing temperature of the archaeological potteries of Maligaimedu, Thiruverkadu and Palur. Sample
Colour
Atmosphere
Clay type
Virtification stage
MM1 MM4 MM6 TK1 TK4 TK6 PL1 PL5 PL6
Red slipped ware Red slipped ware Red ware Red slipped ware Red ware Black ware Red ware Red slipped ware Black and Red ware
Oxidizing Oxidizing Reducing Oxidizing Oxidizing Oxidizing Oxidizing Oxidizing Reducing
NC NC NC NC NC C NC NC NC
IV NV IV CV IV IV EV IV EV
Firing temperature ranges (◦ C) 800–850 <800 750–800 850–950 800–850 800–850 850–950 800–850 800–900
NC: Non-Calcareous; IV: Initial Vitrification; CV: Continuous Vitrification; C: Calcareous; NC: No Vitrification; EV: Extensive Vitrification.
octahedral sheet structure which begins to disappear with increasing temperature and at 500 ◦ C the band disappears completely [1,7]. None of the samples taken for the present study showed the sharp shoulder band at 915 cm−1 . This implies that all the samples were fired to the temperature above 500 ◦ C. According to Yariv and Mendelovici [8] a shoulder band at 875 cm−1 indicates dehydroxylation of Kaolinite minerals which are completed at 800 ◦ C and octahedral sheet structure in the clay mineral disappeared. This again reaffirms that one of the samples from Maligaimedu named as MM1 and all the other remaining Thiruverkadu and Palur samples were fired to a temperature above 800 ◦ C. But the shoulder band does not appear in the Maligaimedu samples MM4 and MM6 because iron content in the samples may be less in quantity and may be fired below 800 ◦ C. The broad absorption bands at 580 and 540 cm−1 have been attributed to Magnetite and Hematite respectively [8–11]. The amount of Magnetite and Hematite decides the reducing or oxidizing atmosphere for firing the artifacts [10,12–14]. The method of firing is very important rather than temperature numbers, as temperature in general is extremely unstable and variable through time and space, within a structure and even on a single
Plate 3. Microphotograph of the sample PL1.
vessel [15,16]. The FT-IR spectra of the samples MM4, TK1 and PL1 show absorption due to hematite indicating that these samples were fired in the open air or perfectly oxidizing atmosphere at the time of manufacture. The less amount of magnetite is due to the transformation of Fe3 O4 to Fe2 O3 during the process of firing [17]. The presence of carbonaceous materials present in the Maligaimedu samples MM1 and MM4 were identified from the infrared vibrational analysis of the spectra of the samples. So charcoal and wood might have been used to fire these samples at the time of manufacture by the ancient artisans belonging to 13th and 14th century AD at Maligaimedu. The pottery shreds TK4 and TK6 show no absorption due to magnetite and hematite because of their low abundance in the samples. The absorption at 535 cm−1 appeared for these samples refired to temperature of 200 ◦ C indicates that these samples were fired in the oxidizing atmosphere. So the artisans of Thiruverkadu were aware of the open air or oxidizing atmosphere technique for firing the potteries made out of the clay materials. The presence of iron, either in pure state or in the form of oxides is the key factor to understand the colour of the potteries. The colour of the pottery is due to the content of iron oxides which acts as the colouring agent. Yariv and Mendelovici [8], Mirti et al. [12,18], and Piero Mirti and Patrizia Davit [13] observed that the colour of the potteries is due to hematite which is a red brown solid and decides the atmospheric conditions (oxidizing/reducing) where the artifacts were fired. The potteries collected from Maligaimedu namely MM1 and MM4, Thiruverkadu potteries TK1, TK4 and Palur samples PL1, PL5 were Red Slipped/Red ware in colour and shows the presence of hematite and hence fired in the oxidizing atmosphere. The black and red coloured potteries PL6 and MM6 probably fired in the reducing atmosphere. This may be due to the air blow into the kiln at the time of firing. Maniatis and Tite [19,20,22], Tite et al. [21], Maniatis et al. [23], Maniatis [24] and Noll et al. [25] have studied the ancient pottery shreds using SEM on similar lines and the development of the vitrification. The approximate firing temperature ranges associated with the various vitrification stages observed in the non-calcareous clays are given by them. The SEM Micro photographs of the samples of interest are shown in Plates 1–3. The pottery shreds MM1, TK4 and PL5 indicate the presence of glassy minerals along with the region of glass areas. This pattern is similar to the one expected
G. Velraj et al. / Spectrochimica Acta Part A 72 (2009) 730–733
out of a clay material of initial vitrification of low refractory, noncalcareous clay type subjected to a firing temperature 800–850 ◦ C [26]. It is understood from the FT-IR studies for the same samples that the atmosphere prevailed at the time of manufacturing is the oxidizing condition and the lower limit of the firing temperature is greater than 800 ◦ C. As shown in Plate 1, the sample MM4 shows no vitrification. Maniatis and Tite [20] have stated that non-calcareous clays fired at temperatures below 800 ◦ C will produce no vitrification. The pottery shreds of low refractory, non-calcareous clay fired in the oxidizing condition was subjected to the firing temperature below 800 ◦ C. The incomplete dehydroxylation exhibited by the pottery shred MM4 in the FT-IR study confirm that the firing temperature value for this pottery shreds is below 800 ◦ C. The pottery shred MM6 was in initial vitrification stage because the glassy fibrous region is along with the region of glass areas. Maniatis and Tite [20] have stated that the low refractory non-calcareous clays show initial vitrification, if they were fired in the temperature range 750–800 ◦ C. The FT-IR studies of this sample also revealed that it was fired below 800 ◦ C under reduced atmosphere. The SEM analysis helped to narrow down the ranges of firing temperature in the interval 750–800 ◦ C. Besides it is in agreement with the FT-IR studies to fix the lower limit of the firing temperature. The pattern and the behavior of the sample TK1 (Plate 2) is similar to the one described by Maniatis et al. [23] for the archaeological potteries. The clay was in continuous vitrification stage of non-calcareous type and fired in the oxidizing atmosphere in the temperature range 850–950 ◦ C. The sample TK6 is of low refractory calcareous type and was in initial vitrification stage and fired in the temperature range 800–850 ◦ C in the oxidizing atmosphere in accordance with the reports of Maniatis [24]. The sample PL1 (Plate 3) show extensive vitrification stage and fired in the oxidizing atmosphere in the temperature range 850–950 ◦ C. The sample PL6 has been fired in the reducing atmosphere in the range of 800–900 ◦ C as it is a non-calcareous type and of extensive vitrification stage as reported by Maniatis [24]. The SEM results of the Palur samples PL1, PL4 and PL6 are consistent with the FT-IR results obtained on the same samples. From the study of the colour and firing temperature of the pottery shreds excavated at the three sites, it is clear that the both open air firing and oxidizing atmosphere conditions were used for firing in kilns in reduced atmosphere by the ancient artisans. So the people lived at the time of manufacture of the potteries in the respective areas of the excavations were aware of the technology of perfection to achieve good quality of their products. They might have used clay containing hematite rich composition to produce potteries. The presence of the black and red colour on the pottery samples studied may be attributed to the blow of air in the closed kiln during the process of firing at reduced atmosphere.
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Acknowledgements The authors are grateful to The Director, The State Department of Archaeology, and also the Head of the department of Ancient History and Archaeology, University of Madras, Chennai, Tamil Nadu, for providing the archaeological samples for this research work. The authors also extended their sense of gratitude to the staff-in-charge of CSIL (Centralized Sophisticated Instrumentation Lab) Annamalai University, Annamalainagar for giving permission to access the FTIR and SEM facility to record the spectra and microphotographs of the samples. References [1] K. Ramasamy, M. Kamalakkannan, Indian J. Pure Appl. Phys. 25 (1987) 284–286. [2] H. Van olphen, J.J. Fripat, Data Handbook for Cal Materials and Other NonMetallic Minerals, Ist ed., Pergamon press, London, 1979, p. 285. [3] R. Sivano, Bertolino, Mariano Fabra, Appl. Clay Sci. 24 (2003) 21–34. [4] R. Palanivel, G. Velraj, Indian J. Pure Appl. Phys. 25 (2007) 501–508. [5] R. Venkatachalapathy, C. Manoharan, T. Sridharan, C.M. Basilraj, Indian J. Pure Appl. Phys. 40 (2001) 207–212. [6] E. Mendelovici, S.H. Yariv, Villalba, Clay Miner. 14 (1979) 323–331. [7] J. Hlavay, K. Jonas, S. Elek, J. Inczedy, Clays Clay Miner. 25 (1977) 451–456. [8] S.H. Yariv, E. Mendelovici, Appl. Spectrosc. 33 (4) (1979) 410. [9] H. Kodama, Infrared spectra of minerals, reference guide to identification and characterization of minerals for study of soils, Tech, Bull, 1985-IE, Research branch, Agriculture, Canada, 1985. [10] D. Barilaro, G. Barone, V. Crupi, M.G. Donato, D. Majolino, G. Messina, R. Ponterio, J. Mol. Struct. 744–747 (2005) 827–831. [11] W. Griffith, in: R.J.H. Clark, R.E. Hester (Eds.), Advances in the Raman and Infrared Spectroscopy of Inorganic Based Materials, Wiley, Chichester, 1987, Chapter 2. [12] P. Mirti, A. Perardi, M. Gulmini, Archaeometry 48 (1) (2006) 31–43. [13] Piero Mirti, Patrizia Davit, J. Archaeol. Sci. 31 (2004) 741–751. [14] S. Akyuz, T. Akyuz, S. Basaran, C. Bolacal, A. Gulec, J. Mol. Struct. 834–836 (2007) 150–153. [15] A. Livingstone Smith, J. Archaeol. Sci. 28 (2001) 991–1003. [16] O.P. Gosselain, J. Archaeol. Sci. 19 (1992) 243–259. [17] G.O. Harrell, R.R. Russell, Influence of Ambient Atmosphere in Maturation of structural products, Bulletin 204, Engineering Experiment station, Chio state University, Columbus, 1967. [18] P. Mirti, M. Gulmini, A. Perardi, P. Davit, D. Elia, Anal. Bioanal. Chem. 380 (2004) 712–718. [19] Y. Maniatis, M.S. Tite, Trans. J. Br. Ceram. Soc. 74 (7) (1975) 229–232. [20] Y. Maniatis, M.S. Tite, Ceramic Technology in the Aegan world during the Bronze Age, Thera and Aegan world I London, 1978, p. 483. [21] M.S. Tite, Y. Maniatis, N.D. Meeks, M. Bimson, M.J. Hughes, S.C. Leppard, Technological studies of ancient ceramics, in: T.A. Wertime, S.F. Wertime (Eds.), Early Pyrotechnology, Smithsonian Institution Press, Washington DC, 1982. [22] Y. Maniatis, M.S. Tite, J. Archaeol. Sci. 8 (1981) 59–76. [23] Y. Maniatis, A. Simpoulos, A. Kostikas, V. Perdikatsis, J. Am. Ceram. Soc. 66 (1) (1983) 773. [24] Y. Maniatis, Firing conditions of white - on - dark ware from Easter Crete, East Cretan white on Dark ware Ed. P.P. Betan court, University of Pennsylvania, 1984, p. 75. [25] W. Noll, R. Holm, L. Born, Painting of Ancient Ceramics, Angewandte chemie, International Edition, vol. 14, 1975, pp. 602–619. [26] M.S. Tite, Y. Maniatis, Trans. J. Br. Ceram. Soc. 74 (1) (1975) 19–22.