Edwards et al17. have stated in their FT-Raman ... oxalate according to Edwards et al17. .... 15 Mc Devitt N T & Baun W L, Spectrochimia Acta, 20 (1964). 799.
Indian Journal of Pure & Applied Physics Vol. 45, June 2007, pp. 501-508
FTIR and FT-Raman spectroscopic studies of fired clay artifacts recently excavated in Tamilnadu, India R Palanivel & G Velraj* Department of Physics, Annamalai University, Annamalainagar 608 002 *Department of Physics, Periyar University, Salem 636 011 Received 4 August 2006; revised 20 February 2007; accepted 16 April 2007 The spectroscopic techniques represent one of the most powerful tools to investigate the structure of all the materials and chemical composition of the cultural objects like potteries, tiles and ceramics. The spectroscopic techniques that have been used in the present study are FTIR absorption and Raman scattering spectroscopy. The potteries maintain aesthetic characteristics so that this type of artifacts can be considered very specific trace of every civilization. Therefore, it is of great importance to acquire knowledge about the chemical composition and the manufacturing techniques of an artifact. From the behaviour of the absorption bands and their corresponding Raman shifts in specific regions and their intensity showing the presence of minerals, traces of elements in the clay, the knowledge of the artisans and the conditions of the temperature control to make qualitatively good materials of archaeological artifacts. The temperature of firing and the vitrification stage are also being established in the case of potteries from the recent excavations at Maligaimedu, Thiruverkadu and Palur in Tamilnadu, India. Keywords: FTIR absorption, Raman shifts, Archaeological Artifacts, Clay minerals IPC Code: G01J3/28
1 Introduction Archaeological materials1 that lie buried in the womb of the earth for centuries also form an interesting aspect of the heritage. The scientific method helps us to unearth and study buried past in a sequential and chronological order2. Potteries have been made of baked clay minerals. The pottery artifacts were selected for the present study owing to their resistance to time and their maintenance of aesthetic characteristics with respect to time. These types of artifacts can be considered as a very specific trace of every civilization. The clay minerals commonly found in the samples and their phase transformations during firing process have been studied by using a number of techniques. In the present study, the mineral compositions present were identified in the potteries artifacts made by the ancient artisans using FTIR and FT-Raman spectroscopy. From the FTIR spectroscopy, the structural composition of the clay in the normal and its transformed state were identified from the changes observed in the characteristic absorptions. To compliment the results of the absorptions exhibited by the pottery artifact samples and confirm the information, FT-Raman spectral data were also used to establish one-to-one correspondence.
2 Experimental Details FT-Raman and FTIR spectra were recorded for the pottery shreds excavated from the archaeological sites namely Maligaimedu, Thiruverkadu and Palur in Tamilnadu state, India. The samples are named as MM1, MM2, MM3, TK1, TK2, TK3, PL1, PL2 and PL3 respectively. The infrared spectra was recorded using KBr pellet sampling technique in Avator 360 FTIR spectrometer in the region 4000-400 cm-1 with the resolution3 of (1 cm-1). The FT-Raman shifts were recorded using a Bruker IFS66 model with FRA 106 Raman model attachment using 1064 nm as exciting radiation of Nd:YAG laser. The Raman spectral shifts were free from fluorescence and accurate to ±4 cm-1 for the entire region of investigation4,5. 3 Results and Discussion In the map of India, Tamilnadu is known for its cultural heritage and civilization for the past 1400 years. The archaeological excavation sites where the pottery artifacts collected are Maligaimedu, Thiruverkadu and Palur. 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
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where n represents the degree of order8. In the case of well ordered Kaolinite n→0. For n=1, the structure becomes more disorder resulting in lllite structure. The change in the order of the clay is occurred due to the presence of Fe, Mg and other composition Al2O3
(19.7%); CaO (11.8%); Fe2O3 (7.3%) and MgO (2.4%) with traces of TiO2, MnO and NiO. The FTIR and FT-Raman spectra of the nine samples are given in the Fig. 1 (a, b and c) and Fig. 2 (a, b and c), respectively. Their tentative vibrational assignments are reported in Tables 1-3 citing the location in the title of the tables, respectively. In IRspectra, Maligaimedu samples MM1, MM2, MM3 show a broad but weak absorption band in the range 3396-3429 cm-1. The band at 3440 cm-1 along with weak band around 1640 cm-1 are attributed to the stretching vibrations of the free hydroxyl group
Fig. 1(a)FTIR spectra of pottery shreds MM1, MM2 and MM3 excavated in Maligaimedu
Fig. 2(a)FT-Raman spectra of pottery shreds MM1, MM2 and MM3 excavated in Maligaimedu
Ancient History and Archaeology, University of Madras, Tamilnadu. The clay minerals present in the pottery shreds can be characterized by the general formula of the type6,7. + 2+ O6Si4 [O4 (OH) 2] [(AlFe)34-2 n Xn ]6−4 n
Fig. 1(b)FTIR spectra of pottery shreds TK1, TK2 and TK3 excavated in Thiruverkadu
Fig. 1(c)FTIR spectra of pottery shreds PL1, PL2 and PL3 excavated in Palur
Fig. 2(b)FT-Raman spectra of pottery shreds TK1, TK2 and TK3 excavated in Thiruverkadu
Fig. 2(c)FT-Raman spectra of pottery shreds PL1, PL2 and PL3 excavated in Palur
PALANIVEL & VELRAJ: FTIR AND FT-RAMAN SPECTROSCOPIC STUDIES OF FIRED CLAY
Table 1FTIR and FT-Raman vibrational frequencies of the pottery samples excavated in Maligaimedu MM1 Frequency FTIR FT-RAMAN
MM2 Frequency FTIR FT-RAMAN
MM3 Frequency FTIR FT-Raman
Tentative vibrational assignment
3688.23 VW
H-O-H str free hydroxyl
3626.83 VW
O-H str. Crystalline Hydroxyls
3396.46 VW
3428.07 W bd
3429.24 W bd
O-H str.adsorbed water
1626.24 VW
1629.94 VW
1629.68 VW
H-O-H bending of water
1587.8 W bd
Carbon black materials
1382.61 VW
Carbonaceous materials
1323.6 M
1329.0 M
Carbon black materials
1042.68 VS
1034.24 VS
1042.31 VS
Si-O str.Clay minerals
793.79 S sp
792.6 M
793.75 W sp
785.2 M
793.44 M sp
788.0 M
Si-O Quartz
691.68 VW
688.00 VW
692.62 VW
Si-O Quartz
646.80 VW
644.61 VW
644.07 VW
Si-O-Si bending
582.39 VW
Fe-O Fe3O4
532.95 VW
527.80 W
532.22 VW
Fe-O Fe2O3
459.46 S
466.41 M
464.18 M
Si-O-Si bending
463.5 W
464.5 M
464.2 M
Si-O of silicates
424.64 W
293.5 W
S-Very strong; S-Strong; M-Medium;W-Weak; VW-Very Weak; bd-Broad; sp-Sharp
Si-O mixed deformation
Si-O of silicates
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Table 2FTIR and FT-RAMAN vibrational frequencies of the Pottery samples excavated in Thiruverkadu TK1 Frequency FTIR FT-Raman
TK2 Frequency FTIR FT-Raman
Tentative vibrational assignment
TK3 Frequency FTIR FT-Raman
3697.05 VW sp
3696.70 VW sp
O-H.str.kaolinite
3433.70 W bd
3434.75 M bd
3433.31 W bd
O-H.str.adsorbed water
1633.61 VW
1632.77 VW
H-O-H bending of water
1600.9 M
1603.6 M
1601.2 M
Carbon black materials
1333.0 M
Carbon black materials
1034.03 VS
1036.96 VS
1030.57 VS
Si-O str.clay minerals
775.96 W
774.01 W
796.1 M
776.33 VW
Si-O quartz
671.41 VW
Si-O quartz
645.87 VW sp
645.63 VW sp
Si-O-Si bending
606.5 M
MnO2
581.66 W
Fe-O Fe3O4
528.54 M sp
Fe-O Fe2O3
502.8 W
538.26 W
Calcium oxalate(hydrated)
469.56 S sp
Fe-O Fe3O4
463.6 W
463.9 S sp
469.92 S sp
Si-O of silicates
431.74 S sp
Si-O mixed vibrations
420.48 S
435.95 M sp
Si-O mixed deformation
292.3 S
Si-O of silicate
VS-Very strong; S-Strong; M-Medium; W-Weak; VW-Very Weak; bd-Broad; sp-Sharp
PALANIVEL & VELRAJ: FTIR AND FT-RAMAN SPECTROSCOPIC STUDIES OF FIRED CLAY
Table 3FT-IR and FT-RAMAN vibrational frequencies of the pottery samples excavated in Palur PL1 Frequency FTIR FT-Raman
PL2 Frequency FTIR FT-Raman 3655.21 VW sp
PL3 Frequency FTIR FT-Raman
Tentative vibrational assignment O-H inner surface
3428.43 W bd
3432.22 W bd
3426.63 W bd
O-H.str.adsorbed water
1638.55 VW
1629.45 VW
1635.31 VW
H-O-H bending of water
1606.9 M
Carbon black materials
1485.9 M
Calcium oxalate
1325.3 M
1041.89 VS
1043.20 VS
1041.17 VS
779.83 VW
790.9 S
776.14 W
788.0 S
774.82 W
786.0 M
Si-O quartz
731.74 VW
732.88 W
Feldspar (orthoclase)
702.41 M
Calcite
690.37 VW
690.24 W
683.65 VW
Si-O quartz
642.98 W
643.25 VW
Feldspar (orthoclase)
MnO2
601.5 M
Fe-O Fe3O4
531.26 M
546.81 M sp
Fe-O Fe2O3, * Si-O-AlIV
476.94 VS
464.3 S
464.2 S
421.96 S
293.0 S
289.7 M
572.81
424.56 VS
Carbon black materials
Si-O str. clay minerals
Si-O-Si bending of silicates
Si-O-Si of silicates
Si-O mixed deformation
Si-O-Si of silicates
VS-Very strong; S-Strong; M-Medium; W-Weak; VW-Very Weak; bd- Broad; sp-Sharp
505
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present in the samples. The dehydroxyl is partly followed by the crystalline framework collapse and tetrahedral heat disorder can be seen from the broadening of the Si-O stretching bands in the region 1100-1000 cm-1 in all the samples9. It is relatively very strong in intensity and merged with 1030 cm-1 band. So it is due to the highly disordered kaolinite. The sample MM2 shows very weak absorption band at 1382 cm-1, which may be due to carbonaceous material10. MM1 and MM3 show absorption band centered around 1040 cm-1, which may be due to the use of mixture of both red and white clay origin. The band at 1034 cm-1 in MM2 may be due to the red clay origin11. The absorption bands centered around 794 and 692 cm-1 are attributed to Si-O mode of quartz present in all the samples. The sample MM2 shows absorption at 688 cm-1. The intensity of the band is very weak. It indicates the size of the quartz particles present in the samples as thick and thin according to the classification made by Elsaces and Oliver9 and Farmer and Russel12. It is inferred that the quartz particles in the sample MM2 are thick. MM1 shows weak absorption band around 582 cm-1 which is due to (Fe3O4) magnetite and (Fe2O3) hematite, respectively. The samples MM1, MM2 and MM3 show absorption band centered around 532 cm-1. So the presence of hematite in the samples is significant as reported in the literature13-16. No infrared absorptions are observed in all the above samples in the region 2000-2600 cm-1. The FT-Raman spectra of the Maligaimedu specimens showing shifts of weak to medium intensity at 2242.1, 2509.4 and 2516.7 cm-1. Edwards et al17. have stated in their FT-Raman spectroscopy studies that the carbon black materials would show shifts at 1600 cm-1 and 1320 cm-1. Based on their observations the bands appearing at 1323.6 and 1329.0 cm –1 in MM1 and MM3 are assigned to the presence of carbon black material in the samples, respectively. The Maligaimedu samples show medium to strong intensity band around 785 and 795 cm-1. This band is assigned to Si-O-Si group of silicates18,19.Alia et al 18. have stated in their studies on application of FTRaman spectroscopy to study the quality control in brick clay firing process, that the Raman band at 776 cm-1 can be assigned to Si-O-Si group in the tetrahedral layer of the phyllosilicates. The presence of band in the region 770-790 cm-1 with weak to medium intensity correspondingly in the infrared
spectra of all the Maligaimedu samples, are assigned to Si-O group. Further, a weak band at 293.5 cm-1 in MM2 assigned to Si-O of silicates The IR spectra of the samples TK1 and TK3 show sharp absorption band around 3696 cm-1 which indicates the O-H stretching of kaolinite present in them. A broad absorption band observed around 3435 cm-1 with medium to weak intensity present in all the three samples due to the adsorbed water10. The weak band of this frequency present in the samples TK1 and TK3 is the indication of the small amount of adsorbed water present in them. In addition, the absorption bands around 1632 cm-1 in the sample TK3 indicate the presence of water molecules. All the samples have silicate band appearing in the region 1100-1000 cm-1. This band is centered around 1034 cm-1 with very strong intensity indicating red clay origin of the kaolinite used in making the potteries. In the samples of Thiruverkadu potteries, the presence of secondary mineral quartz is indicated by the absorption band around 776 cm-1. But the samples TK3 have absorption centered at 645 cm-1 is due to Si-O-Si bending of silicate present in the samples. The iron oxide magnetite and hematite present in the samples TK1 and TK3 are indicated by the sharp absorption band around 469 cm-1. In the sample TK2, it is difficult to identify the absorption band due to magnetite and hematite probably due to the low abundance of these minerals and overlap of absorption band due to silicates13. From the Raman spectra, Thiruverkadu pottery samples TK1, TK2 and TK3 are showing medium intensity bands at 1600.9, 1603.6 and 1601.2 cm-1 due to the carbon black materials, respectively. The specimen TK1 having a band at 1333 cm-1 is assigned to the presence of carbon black materials in the samples. The sample TK2 show medium to strong intensity band around 785 and 795 cm-1. This band is assigned to Si-O-Si group of silicates18,19. The Raman band at 776, 785 cm-1 can be assigned to Si-O-Si group in the tetrahedral layer of phyllosilicates as observed in the sample MM2. The presence of band in the region 770-790 cm-1 with weak to medium intensity correspondingly in the infrared spectra of all the three specimen was assigned to Si-O group. TK2 show medium intensity band at 606.5 cm-1 and identified as MnO2 for manganese dioxide17. A weak band 502.8 cm-1 appearing exclusively in the specimen TK2 is assignable to hydrated calcium oxalate according to Edwards et al17. The weak to
PALANIVEL & VELRAJ: FTIR AND FT-RAMAN SPECTROSCOPIC STUDIES OF FIRED CLAY
medium intensity band around 464 cm-1 present in the samples TK1, TK2 was identified as Si-O of silicates4. A strong band at 292.3 cm-1 in TK2 is assigned to Si-O of silicates20. The IR spectra of the Palur samples PL1, PL2 and PL3 show broad and weak absorption band around 3438 cm-1 and weak band around 1640 cm-1. The sample PL2 show absorption band at 3655 cm-1 which is due to water molecules in the inner surfaces of the samples21. All the three samples have very strong and broad absorption band in the region 1000 cm-1, which is the characteristic of silicate minerals. In all the samples collected from Palur, such band is found to be centered around 1040 cm-1. So it is inferred that the clays of both red and white clay origins are mixed together to prepare the potteries at that time of manufacture. The disordered kaolinite structure present in all the samples are evidenced by the absence of following absorptions at 1100, 1095, 1030 and 1005 cm-1 a weak band at 935 cm-1 and a strong sharp band at 915 cm-1 in the spectra of the samples of the study, respectively. The absorption bands around 780 and 690 cm-1 indicating that the secondary mineral quartz is present in all the samples. Each sample shows the absorption bands centered around 728 and 642 cm-1 are attributed to the characteristic bands of feldspar mineral21. In all the samples, both the quartz and feldspar are identified as secondary minerals. The samples PL2 and PL2 have only magnetite, which is indicated by absorption band at 572 cm-1. These two samples have hematite characteristic absorption bands around 531 and 441 cm-1. The samples PL2 exhibits absorption at 546 cm-1 which is due to Si-O-Al stretching22. From FT-Raman spectra of samples PL2 and PL3 which show shift with weak to medium intensity at 2564.9 and 2451.8 cm-1 are assigned to the carbon black materials according to Edward et al17. The PL3 shows medium intensity band at 601.5 cm-1 which is identified as manganese dioxide17. The weak to medium intensity band around 464 cm-1 in the sample PL3 was identified as Si-O of silicates. A strong band at 293.0 cm-1 in PL1 and weak band at 289.7 cm-1 in PL3 are assigned to Si-O of silicates21 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 3 . Lambert et al 23. and Tominaga
507
et al24. 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. It is inferred that the samples MM1, MM2, MM3, TK2, PL1, and PL2 were red in colour, hence, fired in the oxidizing atmosphere and the remaining samples were red and black ware hence, fired in reducing atmosphere at the time of manufacture. It is inferred from the characteristic bands observed that all the samples of the sites of interest are having disordered kaolinite as principal clay minerals. Further, it is identified that the sample MM2 from Maligaimedu contains carbonaceous materials. The samples MM1 and MM3 have used the mixture of both white and red clay origin, but MM2 have red clay origin of kaolinite. In Palur samples, the mixture of kaolinite of white and red clay origin might have been used for manufacturing the potteries by artisans. All the samples from Maligaimedu, Thiruverkadu and Palur have quartz as secondary mineral, whereas the samples excavated from Palur have quartz and feldspar as secondary minerals. This indicates the artisans of Palur site were aware of the use of both feldspar and quartz as secondary minerals to make good quality, good appearance and good strength potteries for their living purposes. The pottery shreds excavated from the three sites have been found to contain the magnetite and hematite as accessory minerals in them. From the amount of these minerals, one can able to understand the colour, the type of potteries and the atmospheric condition of firing process adopted by the artisans at that time. The range of firing temperature and the supposed method of firing technique are also inferred from the colour and visual appearance of vitrification of the excavated samples, respectively. Acknowledgement 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 are thankful to the Director of RSIC, IIT Madras, Chennai, now it is named as SAIF (Sophisticated Analytical Instrumentation Facility) for his help to record the FT-Raman spectra of the samples. The authors also extended their sense of gratitude to the staff-in-charge of CSIL (Centralized
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Sophisticated Instrumentation Lab) Annamalai University, Annamalainagar, for giving permission to access the FT-IR facility to record the spectra of the samples. References 1
Barker P, Techniques of archaeological excavation, (Batsford, London), 3rd Edn (1982) p.1. 2 Raman K V, Cultural heritage of the Tamils, edited by Subramanian.S V & Veerasami V, (International Institute of Tamil studies, Adaiyar, Chennai), 1981, p.211. 3 Russell J D, A handbook of determinative methods in clay mineralogy, (Edited by Wilson M J & Blackie) (1987) pp. 135-137. 4 Edwards H G M & Farewell D W, Spectrochim Acta, 51(A) (1995) 2073. 5 Edwards H G M & Farewell D W & Daffier, Spectrochim Acta, 52 (A) (1996) 1639. 6 Ramasamy K, Duraisamy D & Venkatachalapathy R, Proc of the International colloq on the role of chem. in archeology, edited by Ganorkar M C & Rama Rao N, (Hyderabad, India), 1991, p 47-54. 7 Prasad J, Trans Indian Ceram Soc, 24(3) (1965) 78. 8 Keeling P S, Trans Brit Ceram Soc, 63(7) (1963) 549. 9 Elsaces P & Oliver D, Clay Minerals, 13 (1978) 299. 10 Sankaran S & Ramasamy K, Asian J Phys, 9(2) (2000) 362. 11 Gosh S N, J Mater Sci, 13 (1978) 1677. 12 Farmer V C & Russel J D, Spectrochimica Acta, 20 (1968) 1149.
13 Russell J D, A handbook of determinative methods in clay mineralogy, edited by Wilson M J & Blackie & Son Ltd), 1st Edn, 1987, p.163. 14 Kodama H, 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. 15 Mc Devitt N T & Baun W L, Spectrochimia Acta, 20 (1964) 799. 16 Venkatachalapathy R, Manaoharan C, Sridharan T & Basilarj C M, Indian J of Pure & Appl Phys, 40 (2001) 207. 17 Edwards H G M , Farewell D W , Rull Perez F & Medina Gracia J, Analyst, 126 (2001) 383. 18 Alia J M , Edwards H G M,Gracia Navarro F J , ParrasArmenteres J & Sanchez Jimenez C J, Talanta, 50 (1991) 291. 19 Dowty E, Phys Chem Miner, 14 (1987) 122. 20 Palanivel R & Velraj G, Proc of the National Seminar on Advances in Materials Science, Department of Physics, Manonmaniam Sundaranar University, (Tirunelveli, Tamilnadu), 2006, p.71. 21 Palanivel R & Velraj G, Proc of the National Laser Symposium, Department of Physics, Vellore Institute of Technology, (Vellore, Tamilnadu) 2005, p 350. 22 Zwinkels J C & Michaelian K H, Infrared Phys, 25 (1985) 629. 23 Lambert, J B, Xuel, Weydart, J M & Wiltner ,J H, Archaeometry, 32(1) (1990) 47. 24 Tominaga T, Takeda M & Mabuchi, H, Archaeometry, 20 (1978)135
