Minerals and Metals in Ancient India v1.c29.s1: What Next? Required More Analytical Investigations
Minerals and Metals in Ancient India v1.c29.s1
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What Next? Required More Analytical Investigations
v1.c29.s1.1
It must be emphasized that the conclusions reached and stated above (1-11) are tentative, and we would not be upset if new findings alter some or all the conclusions. After all, history means re-interpretation of the past which implies that new facts about the past may be discovered and taken note of.
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Whatever analytical work has been done so far regarding the ancient Indian artefacts is small compared to how much more can and should be done. Thousands of samples have remained untouched, and we do not know even their elemental compositions. Very few icons have been scanned metallographically, and phase analyses of most of the artefacts and residues such as slags are yet to be undertaken.
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Fortunately the recent trend of research is encouraging and we may cite some examples which are worthy of emulation. Craddock (1981: 20) analysed 121 Tibetan and Himalayan icons/metalworks by atomic absorption spectrophotometer which permitted him to assay 13 elements in each sample down to 10 ppm level. These analyses had a precision of ± 1 per cent for major elements and ± 20 per cent for the trace elements. Though the sensitivity of this technique is high, it necessitates dissolution and a separate analytical scrutiny for each element to be determined.
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Nieuwenhuysen et al. (1984: 105) preferred the non-destructive procedure employing scanning electron microprobe which allowed the selection of the sample area to be anlaysed through the use of light microscopy, secondary electrons and back-scattered electrons. Subsequently, by analysing the scanning electron beam induced X-ray fluorescence with an energy dispersive detection system (EDAX), the simultaneous detection of a large number of elements was made for 23 Himalayan metal statues in the Museum of Antwerp.
v1.c29.s1.5
Transmission and scanning electron microscopy combined with diffraction study and EDAX facilities permitted us to study heterogeneity, elemental composition, grain size and grain phase composition of ancient zinc slag in a comprehensive manner. (Biswas et al., 1984: 236-37) Using a fine electron probe (~ 50 nm diameter) we could scan a grain as small as 0.5 µm and quantitatively analyse ten elements therein; we could also report the presence of more than a dozen specific phases in the lead-zinc bearing slag. Freestone and Middleton (1987) have shown how analytical SEM combined with DTA, electron petrography and thermodynamics of phase diagrams can yield valuable informations about silicate and carbonate-based artefacts, like ancient pottery and porcelain and archaeological residues like the zinc slag of Zawar Mines.
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We have also demonstrated (Biswas, 1989: 20-21) that selective area electron diffraction (SAED) pattern analysis in transmission electron microscopy (TEM) reveals the X-ray amorphous phases and explained how simultaneous EDAX studies with secondary as well as back-scattered electrons permitted us to quantitatively determine as many as 14 elements in a narrow zone of 0.1 µm. These techniques have tremendous possibilities in the analysis of archaeological samples. The family of photo-electron spectroscopy (PES) techniques such as ESCA or electron spectroscopy for chemical analysis involves the short escape depth of the excited electrons, and therefore can provide special information about a very thin surface layer (such as in gilded icons) as contraposed to the information of the bulk. Electron energy loss spectroscopy or EELS is ideally suited for the study of low atomic number elements in artefacts and archaeological residues.
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Neutron activation analysis is another non-destructive technique for assaying trace elements which is based on the radio-activity of neutron-irradiated samples (and the standards for each element). The energies and the spectra of the emitted gamma rays are utilised to assay in terms of a set of chosen elements. Iyer *et al.* (1973) estimated Na, Mn, La, Sc and Cr in neutron-irradiated samples to characterise Indian potsherds obtained from different geographical localities. Bhoraskar *et al.* (1985) estimated the relative activities of Cu, Al, Mn, Mg and Si in the neutron-irradiated iron samples from five megalithic sites and the seventh century BC smelting site of Naikund, Maharashtra. Since the activity ratios were similar, they concluded that the Naikund smelter was the source of the artefacts found in the five different places.
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Mossbauer spectroscopy is applicable to ferrugenous archaeological materials such as iron artefacts (Rai and Rajan *et al.*, 1985), NBP ware slip (Rai and Roy, 1980-81) etc. The latter has been shown to contain amorphous orthopyroxene and bears a Fe²⁺/Fe³⁺ ratio around 4.5.
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Raj and Sundaram (1990: 27) carried out a few evaluations on some famous Indian bronze icons using high resolution radiography with sensitivity levels of 30 µm, and confirmed that these castings do not contain even minute defects at the most intricate and difficult to cast portions. They have recommended the following sophisticated techniques for detailed evaluation of Indian icons, the Delhi Iron Pillar, Wootz steel etc:
v1.c29.s1.10
*In situ* metallography for micro-structure, with quantitative image analysis for phase contents and slag distribution, microphotography and laser contouring for precise dimensional appreciation, high-sensitivity X-radiography, ultrasonic testing, emf and electrical conductivity measurements for volume evaluation/characterisation; X-ray fluorescence and neutron activation analysis for chemical composition; structure-property correlation studies, fractal analysis on wootz, micromorphology of wootz crucible material.
v1.c29.s1.11
The last few items as stated above were suggested towards development of high-strength superplastic high-carbon steels — some success has been achieved in this regard by some American scientists while trying to replicate wootz — and of high performance ceramic materials resembling wootz crucibles.
v1.c29.s1.12
To the above list of techniques as given by Raj and Sundaram (1990: 27) we would like to add the suggestion for the various categories of analytical electron microscopy (diffraction, transmission and scanning) techniques such as Convergent beam diffraction (CBD), Electron energy loss spectroscopy using plasmon peaks (EELS-PL), High resolution electron microscopy-lattice imaging (HREM), Energy-dispersive X-ray micro-analysis (EDAX) etc.
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We should also record the great necessity for replication experiments. There are great questions and theories as to how the artefacts were made, using what manufacturing conditions. The theories should be tested through actual experimental efforts based on the hypothesized procedures. We have mentioned such replication experiments related to copper-making, high iron copper, NBPW and its glaze etc. The results of such experiments would be very instructive though not always conclusive.