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Bronze technology of the ancient megalithic communities in the Vidarbha region of India
Journal of Archaeological Science 40 (2013) 3811e3821
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Bronze technology of the ancient megalithic communities in the Vidarbha region of India Jang-Sik Park a, *, Vasant Shinde b,1 a b
Department of Metallurgical Engineering, Hongik University, 2639, Sejong-ro, Jochiwon-eup, Sejong 339-701, Republic of Korea Deccan College, Post-Graduate & Research Institute, Deemed University, Pune 411006, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 July 2012 Received in revised form 21 May 2013 Accepted 25 May 2013
Metallographic examination was carried out on forty-nine copper and bronze objects from five megalithic sites located in Vidarbha, India. The artifact assembly consists of horse ornaments, kitchenware, bangles, rings, small bells and the hilt of an iron dagger. Results show that the technology involved is characterized by the use of bronze alloys containing approximately 10% tin based on weight and the application of forging as a key method of fabrication. No deliberate addition of lead was observed. Arsenic was detected, but very rarely and only as an insignificant minor element. The consistent selection of such specific alloys indicates that the megalithic communities in this particular region had established a fully developed and standardized bronze tradition optimized for the production of forged items. Their advanced technological status was also noted in a special technique applied to two forged high-tin bronze bowls. Such a unique bronze tradition, dedicated to sheet metal technology, was most likely a practical choice made by these people to take advantage of the changing role of bronze. Specifically, with the introduction of iron, bronze seems to have become a more prestigious material that could serve as an indicator of the appearance of a more rigid socio-economic stratification within the megalithic communities of the Vidarbha region. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: India Megalithic period Bronze technology Chemical composition Microstructure
1. Introduction The megalithic period in India, which began approximately in the early first millennium BC, is notable for the emergence of iron metallurgy and new burials, referred to as megaliths. In a companion article (Park and Shinde, 2013), our team examined iron objects from five megalithic sites located in the Vidarbha region of the Maharashtra state (Fig. 1). The result showed that these megalithic communities shared a fully developed and wellstandardized iron technology of substantial flexibility. In this paper, we focus on the bronze objects excavated from the same megalithic sites and characterize the technology applied in their fabrication. The sites were all closely located and dated to the first half of the first millennium BC based on typological grounds (Thakuria, 2010: 67e73). This chronology is in fair agreement with the radiocarbon age of one of the sites at Bhagimohari as reported in the data set compiled by Possehl and Gullapalli (1999). Their
* Corresponding author. Tel.: þ82 44 860 2562; fax: þ82 44 866 8493. E-mail addresses: [email protected], [email protected] (J.-S. Park), [email protected] (V. Shinde). 1 Tel./fax: þ91 20 26513203. 0305-4403/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jas.2013.05.030
intimate relationship was also confirmed in the external appearance and purpose of iron and bronze objects excavated. The iron objects from them were mostly for tools and weapons while the bronze objects consisted primarily of ornaments and kitchenware. More information on the archaeological context of the sites and findings may be found in the companion article mentioned above. Bronze making begins with a determination of the alloying elements and the amounts needed to meet certain material properties required for fabrication and use. In antiquity, tin (Sn), arsenic (As) and lead (Pb) served as the major elements that could be deliberately added to copper (Cu). The presence of these elements in copper lowers the melting temperature and improves the flow property of the molten alloys. This helps to facilitate the process of casting. In addition, tin and arsenic aid in the strengthening of the alloys, thereby allowing objects of a similar purpose to be made with less material. It should be noted that adding lead may lower material costs and promote better casting, but it may also sacrifice the impact resistance and the load-bearing capacity of the end product. Bronze objects can be fabricated either exclusively through casting or by a more complex process involving substantial forging once initial casting has been completed. In the latter case, forging is the primary method for shaping the material, during which
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was established in the megalithic communities of South India. Her major concern, however, dealt with the use of high-tin bronze, and it is not clear if her results can accurately represent the general bronze traditions practiced in the region at that time. The data compiled by Kenoyer and Miller on the chemistry of Indus objects constitute a rare reference for comparative studies in ancient Indian bronze technology. Their data show that of the Indus objects examined copper alloys with added tin occupy less than 30% of the assemblage. In addition, and more importantly, tin levels were found to vary substantially. Lead was added only in certain exceptional cases. 2. Comments on artifacts
Fig. 1. Map of India. (a) The Indian subcontinent with the city of Nagpur indicated by the arrow; (b) the state of Maharashtra with the city of Nagpur marked by the asterisk within the shaded region of Vidarbha. Spots 1e5 denote the sites at Borgaon, Khairwada, Bhagimohari, Mahurjhari and Raipur, respectively, from which the bronze objects under review were recovered.
noticeable strengthening can also occur. It is important to note that the method of fabrication must be carefully selected with the chemical composition of the alloys in mind. The process of combining alloy compositions with proper fabrication techniques can lead to the establishment of a bronze technology, one that will reflect the availability of resources, the cultural traditions, and the technological advancements of its practitioners. Thus, the characterization of an established bronze tradition may provide further insight into the socio-cultural environment and influential trade networks of a given community. Unfortunately, bronze objects of Indian megalithic communities have not yet been thoroughly explored as valuable archaeological materials bearing important information on megalithic culture. In fact, megalithic bronze tradition has drawn only marginal attention, and not much is known of the technological aspects characterizing this tradition in comparison to that of other communities with varying regional or chronological contexts. In this respect, the research conducted by Srinivasan (1998) and by Kenoyer and Miller (1999) serves as a useful source of information. According to Srinivasan, a highly sophisticated bronze technology
Fig. 2 shows the general appearance of the forty-nine bronze objects examined, all of which are currently on display in the megalithic room of the Deccan College Museum. The assembly consists of ten bangles (objects #1, 5, 9, 10, 23e25 and 44e46), an ornament (#2), two rings (#3 and 4), three bells (#6, 26 and 49), six dishes (#7, 8, 30, 32, 33 and 48), nineteen horse ornaments (#11e22 and 37e43), six bowls (#27e29, 31, 34 and 36), the hilt of an iron dagger (#35) and a pot (#47). The artifacts were recovered through controlled excavations at five megalithic sites (see Fig. 1) in the Nagpur district of the Maharashtra state. Two objects (#1 and 2) are from Borgaon, six objects (#3e8) are from Khairwada, two objects (#9 and 10) are from Bhagimohari, twenty-nine objects (#11e36 and 47e49) are from Mahurjhari, and ten objects (#37e46) are from Raipur. The bar near each object in Fig. 2 corresponds to 1 cm unless otherwise noted. Brief information about the usage and recovery site of each object is provided in Table 1. The artifact numbers are consistent between Fig. 2 and Table 1, and lower case letters have been used to differentiate individual parts of a given object containing multiple pieces. For cases involving two or more specimens taken from a single piece, their locations are marked in the object by arrows a1, a2 and a3. It should also be mentioned that objects #39c and 39d are almost identical in shape and size to #14 and 15, and are displayed in #39 as the components of one artifact. Visual inspection of the assemblage under investigation revealed several significant facts. First, the objects were mostly fabricated from thin metal sheets; however, the three bells and ten bangles are notable exceptions. The bells were intended for horse ornaments and are generally similar in shape and size. Two of them (#6 and 49) contain two parts assembled near the shoulder while the other bell (#26) consists of one single piece. Second, the assemblage can be classified into two distinct groups, one consisting of ornaments for either humans or horses and the other containing domestic items such as bowls and dishes. Third, the assemblage has no tools or weapons. It should be noted that with regard to object #35 the item is merely a hilt, not the iron dagger itself, and is therefore not much different from an ornament. 3. Laboratory examination and results Small specimens were taken from the objects and then mounted, polished and etched with a solution of 100 ml methyl alcohol, 30 ml hydrochloric acid and 10 g ferric chloride. Their microstructures were examined using an optical microscope and a scanning electron microscope (SEM). The alloy composition was measured using the energy dispersive x-ray spectrometer (EDS) included with the SEM instrument. This information is reported in Table 1 according to weight fraction. The tin level is given to the nearest whole digit. For the other minor alloying elements (i.e., sulfur, iron, lead and arsenic), their levels are provided to within 0.5%, even though the EDS instrumentation is capable of providing
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Fig. 2. General appearance of the bronze objects examined. Objects #1 and 2 are from Borgaon; #3e8 are from Khairwada; #9 and 10 are from Bhagimohari; #11e36 are from Mahurjhari; #37e46 are from Raipur; and #47e49 are from Mahurjhari. The objects consist of 10 bangles (objects #1, 5, 9, 10, 23e25 and 44e46), an ornament (#2), 2 rings (3 and 4), 3 bells (#6, 26 and 49), 6 dishes (#7, 8, 30, 32, 33 and 48), 19 horse ornaments (#11e22 and 37e43), 6 bowls (#27e29, 31, 34 and 36), the hilt of an iron dagger (#35) and a pot (#47). The bar near each object corresponds to 1 cm unless otherwise noted. The numbers labeling the objects are consistent with those in Table 1. The lower case letters used distinguish multiple parts of an object. The labels a1 and a2 denote the locations from which two specimens were taken from a single part of an object.
accuracy readings to within a few tenths of a percent. The average composition of each specimen was inferred from the EDS spectrum taken in a raster mode. In general, the area of each specimen was approximately 0.65 0.45 mm, except in cases where restrictions on the specimen size necessitated a smaller sample.
3.1. Microstructure Fig. 3aef show optical micrographs of the structures of objects #12a, 39c, 39b, 40, 27 and 18, respectively. These structures consist primarily of the a phase in the CueSn system. The a grains are seen
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Table 1 Summary information, including chemical compositions, for the bronze objects examined from megalithic sites at Nagpur in the Maharashtra province of India. The numbers labeling the objects are consistent with those in Fig. 2. Artifact # (# in Fig. 2)
Description of artifact (largest dimension in cm)
Site
1 2 3 4 5 6 7
Bangle (7.2) Ornament [rod with a bulged end] (2.5) Ring (2.1) Ring (2.3) Ring (5.6) Horse ornament [Bell] (10.0) Dish with a lid (8.4) Rim Wall Lid Dish with a lid (5.1) Rim Wall Lid Small bangle (3.9) Bangle (8.4) Horse ornament cut from a plate (24.0) Horse ornament (7.8) Rod rolled from a sheet Crescent cut from a sheet Horse ornament (9.5) Rod rolled from a sheet Shape cut from a sheet Hollow hemisphere with a little rod attached across the bottom (2.5; 2.1) Horse ornament cut from a plate (10.2) Horse ornament (7.3) Edge of the object rolled into a rod Main body cut from a sheet Circular horse ornament with a domed center (6.0) Circular horse ornament with a conical center (7.1) Circular horse ornament with a domed center (6.0) Circular horse ornament with a conical center (6.0) Circular horse ornament with a conical center (7.2) Bangle (10.1) Bangle (6.6) Bangle (5.5) Horse ornament [Bell] (10.5) Bowl (15.5) Bowl (12.0) Bowl (12.5) Dish (26.0) Rim Bottom Bowl (17.0) Dish (14.0) Dish (13.5) Bowl (18.0) Hilt of an iron dagger (9.0) Bowl [Bone inside] (14.2) Horse ornament in the form of a rectangular rod rolled from a sheet (13.1) Horse ornament cut from a sheet (9.1) Horse ornament (25.0) Rectangular rod with ringed ends and attached to the bottom of#39b Main body cut from a plate Hollow hemisphere with a little rod attached across the bottom (similar to #14 and 15) Horse ornament cut from a sheet (9.6) Horse ornament (13.3) Rod rolled from a sheet Main body cut from a sheet Circular horse ornament with a conical center (7.9) Horse ornament cut from a plate (8.2) Bangle (6.0) Bangle (6.0) Bangle (5.3) Pot (19.0) Rim Wall Bottom Dish on an 11-legged stand (11.5) Horse ornament [Bell] (10.0)
Borgaon
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
a1 a2 b a1 a2 b
a b a b
a1 a2
a1 a2
31 32 33 34 35 36 37 38 39
a
b c d 40 41 42 43 44 45 46 47
48 49
a b
a1 a2 a3
Composition (wt.%) Sn
e none detected; tr trace amount.
Khairwada
Bhagimohari Mahurjhari
Raipur
Mahurjhari
Fabrication method
S
Fe
Pb
As
7
0.5
e
e
e
1 e 2 6 1 1 1 9 8 8 8 11 6 10 9 9 8 10 9 11 12 12 11 11 11 8 12 9 8 9 12 9 10 6 9 10 8 6 17 10 10 9 11
0.5 0.5 1.0 1.0 e 0.5 e e e e 0.5 e 1.0 e e tr tr 0.5 tr 0.5 0.5 0.5 e 0.5 e 1.5 0.5 e 0.5 0.5 tr 1.5 0.5 0.5 0.5 0.5 0.5 e e tr 0.5 tr 0.5
e e e 0.5 tr 0.5 1.0 1.0 0.5 0.5 e e 1.0 e e 0.5 0.5 0.5 e e e e e e e 1.5 e e 0.5 1.0 0.5 e 0.5 0.5 0.5 0.5 0.5 0.5 tr 0.5 tr 0.5 0.5
e e e 0.5 e e e tr tr e tr e e e tr e e e e e e e e tr e e e e e e tr e e tr e e e 0.5 e e e e 1.0
e e e e e e e e e e e e e e e e e e e e e e e e e e e 5.0 e e e e e 1.5 e e e 1.5 e 1.0 e e e
Forged Cast Forged Forged Forged Cast Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Cast Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged
11 1
0.5 e
0.5 0.5
1.0 tr
e e
Forged Forged
9 9 9
0.5 e e
1.0 e e
e e e
e e e
Forged Forged Forged
10 8 9 8 10 9 9 8 10 10 9 18 6
e tr e e e 0.5 0.5 tr 0.5 0.5 0.5 0.5 e
e 0.5 e 0.5 e e tr tr 1.0 1.0 0.5 e e
1.00 e e e e e e e e e e e tr
e e e e e e e 0.5 e e e e e
Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Cast
Comments
Corroded; a-dendrite
Trace Bi
Trace delta phase Trace delta phase
Trace delta phase
b-Martensite phase
Retained g-phase
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Fig. 3. Optical micrographs. (a)e(f) Microstructures of specimens taken from objects #12a (horse ornament), 39c (horse ornament), 39b (horse ornament), 40 (horse ornament), 27 (bowl) and 18 (horse ornament) in Fig. 2, respectively.
to contain straight twin boundaries, indicating that the objects were more or less subjected to plastic deformation during fabrication. The dark particles or ribbons scattered over the bright a background correspond to non-metallic inclusions of copper sulfide. Their density was determined during the copper smelting process and was influenced by the character of the ores used. Their shape, however, was decided during fabrication, and the sulfides were elongated to such an extent as to form continuous horizontal layers as seen in Fig. 3e. These conditions reflect the extreme degree of forging applied to object #27. The low density of twins in Fig. 3b, along with less deformed inclusions, demonstrates that object #39c was given minimal forging. A similar microstructure was also observed in objects #11, 12 and 39d, which are almost identical in shape to object #39c. Furthermore, the microstructure in Fig. 3f is unique in that it has a small a-d eutectoid located in the dark irregular regions. Fig. 4aed present typical results obtained from the SEM analyses. Fig. 4a, an EDS spectrum from the entire area of Fig. 3c, shows the presence of major elements, copper (Cu) and tin (Sn), along with other minor elements, sulfur (S) and iron (Fe). The carbon (C)
peak in this spectrum, as well as in those that follow, is due to the thin carbon coating applied for the purpose of this SEM examination, and can be ignored. The approximate average composition of the specimen as inferred from Fig. 4a is 9% Sn, 0.5% S, and 1.0% Fe plus balance copper. Here, tin is the only element that was added intentionally during alloy making. By contrast, sulfur and iron were included inadvertently. Fig. 4b, an EDS spectrum from one of the inclusions marked by the arrow in Fig. 3c, shows the inclusion to be a particle of copper sulfide containing a substantial amount of iron and a slight amount of selenium (Se). Fig. 4a and b represent the EDS spectra obtained from the majority of the objects examined, with only minor variations detected in a relative fraction of the elements present. One notable exception found was that certain specimens contained lead (Pb) in a trace amount. These lead particles were more easily identified using the SEM micrographs than the optical micrographs as seen in Fig. 4c, an SEM micrograph magnifying the area near the arrow in Fig. 3d. Fig. 4c shows bright particles of almost pure lead formed during solidification due to the limited solubility of the material in solid copper. Fig. 4d, an EDS spectrum taken from one of the lead particles marked by
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Fig. 4. EDS spectra and SEM micrograph. (a) EDS spectrum taken from the entire area shown in Fig. 3c; (b) EDS spectrum taken from the arrow in Fig. 3c; (c) SEM micrograph enlarging the area marked by the arrow in Fig. 3d; (d) EDS spectrum taken from the arrow in (c).
the arrow in Fig. 4c, shows that the major constituent is lead. The presence of chlorine (Cl) resulted from the applied etching solution which contained this element as a constituent. It is, therefore, irrelevant to the particle’s original composition and can be disregarded. The analytical results from most of the objects examined were fairly consistent and well represented by the micrographs and EDS spectra presented in Figs. 3aef and 4aed. There were, however, notable exceptions where different alloys were used. In some cases, different thermo-mechanical treatments were applied as well during fabrication. Fig. 5aef, optical micrographs of the specimens from objects #3, 23, 33, 48, 6 and 26, respectively, illustrate the varying microstructures produced when alloy compositions and thermo-mechanical treatments differed. The results in Fig. 5a closely resemble those of the previous optical micrographs where elongated sulfide inclusions were scattered over the twinned a background. The EDS analysis, however, showed the tin content to be approximately 1%, which is too small to be considered a result of intended alloying. The structures presented in Fig. 5bed are exceptional in that they do not consist of a single a phase but rather contain minor second phases. Formation of the latter, reflecting an increase in the level of alloying elements, is the most likely explanation of the visible contrasts seen in these particular micrographs. Specifically, in Fig. 5b, the presence of 5% arsenic and 9% tin was responsible for the formation of a second phase in the bright areas scattered over the darker a background.
By contrast, the second phases in Fig. 5c and d correspond to bmartensite and retained g, respectively. Such results would be expected in high-tin bronze alloys with a tin content approaching or exceeding 15%. Moreover, this type of second phases would not be expected to form during slow cooling; rather, it would be obtained only after quenching. For this sample, the presence of bmartensite indicates that the specimen was quenched at or above 600 C while the retained g phase suggests that quenching was performed at a temperature between 520 C and 586 C. It is also important to note that for Fig. 5c and d the average tin level measured was 17% and 18%, respectively, with no other alloying elements detected. For Fig. 5e and f, the structural characteristics determined during the solidification reaction were more or less retained without any evidence of thermo-mechanical treatments being applied after casting. It is evident, therefore, that objects #6 and 26 (two bells), as seen in Fig. 2, were fabricated exclusively through casting. The tin levels were found to be approximately 6% in Figs. 5e and 12% in Fig. 5f. Of particular importance are the large dark areas in Fig. 5f. These represent shrinkage cavities due to volume contraction during freezing. Their presence in this higher tin object (#26) is likely associated with the fact that it was cast from a single piece while the lower tin object (#6) was made of two separately cast pieces that were later assembled together. The increased tin content apparently, however, did not compensate for the difficulties arising from the complex geometry to be cast.
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Fig. 5. Optical micrographs. (a)e(f) Microstructures of specimens taken from objects #3 (ring), 23 (bangle), 33 (dish), 48 (dish with a stand), 6 (bell) and 26 (bell) in Fig. 2, respectively.
Fig. 6aed show the results of the SEM analyses on the second phase areas observed in Fig. 5b and d. Fig. 6a, an SEM micrograph enlarging the area marked by the arrow in Fig. 5b, depicts a twophase region present in the a background. Fig. 6b, an EDS spectrum of the entire area of Fig. 5b, shows this specimen to contain both tin and arsenic as alloying elements. The average tin and arsenic levels inferred from Fig. 6b were approximately 9% and 5%, respectively. The EDS analyses for arrows 1e4 in Fig. 6a show that the approximate alloy contents at each arrow correspond to 11% Sn6% As, 12% Sn-7% As, 16% Sn-7% As and 29% Sn-3% As, respectively. These results indicate that the two-phase region was caused by a eutectic reaction between the a (arrow 3) and d (arrow 4) phases of the ternary CueSneAs system. This reaction was made possible by a solute enrichment brought on by elemental segregation during solidification. Thus, the increase in tin and arsenic levels from arrows 1 to 2 suggests that both elements were enriched toward the two-phase region as solidification progressed. Fig. 6c, an SEM micrograph magnifying the area marked by the arrow in Fig. 5d, shows the presence of another second phase, g, along with the major phase, a. The tin content of this g phase is
approximately 27%, as inferred from Fig. 6d, an EDS spectrum taken from the arrow marking one of the g areas. It is important to note that the g phase becomes unstable below 520 C and undergoes eutectoid phase transformation between the a and d phases of the binary CueSn system. Thus, since the g phase was retained in this particular specimen, it is apparent that the artifact examined underwent a special thermal treatment similar to the one described above. 3.2. Chemical composition Table 1 summarizes the chemical composition of the forty-nine objects examined. Some of them (#7, 8, 12, 13, 39 and 41) represent an assemblage of two or more separate parts, each of which produced an individual specimen. For objects #7, 8, 17, 30 and 47, more than one sample was taken from each object or part. The elemental distribution, as observed in the multiple specimens taken from the single samples (#7a1-a2, 8a1-a2, 17a1-a2 and 43a1-a3), is relatively uniform as noted in Table 1. This suggests that the composition data represent the objects under investigation.
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Fig. 6. SEM micrographs and EDS spectra. (a) SEM micrograph magnifying the area marked by the arrow in Fig. 5b; (b) EDS spectrum from the entire area of Fig. 5b; (c) SEM micrograph magnifying the area marked by the arrow in Fig. 5d; (d) EDS spectra from the arrow in (c).
Table 1 shows that the majority of the specimens listed contain tin as a major alloying element, along with several minor constituents such as sulfur, iron, lead and arsenic. Sulfur and iron, present in a number of specimens, presumably were added inadvertently during smelting. It is important to note, however, that the sulfur detected was a constituent of copper sulfide inclusions which were often iron-contaminated. By contrast, the iron existed as a solute element in the metallic a phase. Lead was also detected in some specimens, though only at a fraction of 1% or below. This indicates that it was not intended but rather added inadvertently by the use of lead-contaminated ores in smelting (Craddock, 1979). One may, therefore, assume that the presence of sulfur, iron and lead is completely fortuitous. In addition, since these elements appeared in such small amounts, their effects on the material properties of the objects in question would have been minimal, at best, meaning they probably would have gone unnoticed. As for the presence of arsenic, this element was added, most likely during the smelting process through the use of specific ores. In this case, noticeable effects on alloy properties would have been observable when its fraction exceeded 1%. Given these conditions, it is apparent that tin and arsenic were the only alloying elements intended. The specimens in Table 1 can be classified into three groups based on their tin levels. First, objects #3e5, 7a1, 7a2, 7b and 39a constitute a low-tin group where each member contains 2% tin or less. Second, objects #33 and 48, with 17% and 18% tin respectively, represent a high-tin group. Third, all other objects belong to a group where the tin level ranges from 6% to 12%. It should be noted that
for the last group the tin content generally falls within a narrow window of 8%e12%, with the six exceptions being objects #1, 6, 11, 29, 32 and 49. For objects in the first group, a tin level below 2% is too small to be considered intended. Thus, members of the low-tin group are herein referred to as copper objects while the term bronze is reserved for members of the higher-tin groups only. Table 1 lists four objects (#23, 29, 32 and 34) in which arsenic is present. All of them contain 6%e10% tin with arsenic detected as a minor alloying element. It is important to note that in two cases (#29 and 32) the specimens contain 6% tin. This tin level is the lowest of the group they belong to and departs significantly from the average composition of the group. In general, arsenic addition in copper, which usually takes place during smelting, not only lowers the melting temperatures but also promotes work hardening (Lechtman, 1996). As such, the reduced tin concentration in the two objects above may not be fortuitous, but was likely associated with the presence of 1.5% arsenic in both. Table 1 contains only four objects (#2, 6, 26 and 49) that were shaped through casting without forging. For object #2, the specimen was severely corroded and its composition could not be determined accurately. Evidence, however, from EDS and microstructure analyses showed it to contain a substantial amount of tin. For objects #6 and 49 (two of the three cast bells), the tin content was determined to be 6%. It should be mentioned that in virtually every specimen examined in the bronze groups, the tin fraction was controlled to a range of 8%e12%, with notable exceptions being the cast objects #6 and 49 and the arsenic-added objects #29 and 32.
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4. Discussion The results in Table 1 show that the bronze tradition of the five megalithic communities in Vidarbha was established consistently on the basis of forging as a primary means of fabrication and the use of CueSn alloys of near 10% tin content as major materials. This consistency in technological aspects is in agreement with the prediction based on artifact typology. All except four of the objects examined were fabricated through forging, mostly in the form of thin sheets. Approximately 90% of the objects were made of bronze alloys with 6% tin or greater, predominantly with tin levels between 8% and 12%. Arsenic was also added, but only in four of the objects under review and as a minor constituent in supplementing tin. Other elements such as sulfur, iron and lead were detected in a number of specimens, but only in trace amounts such that their presence may have gone unnoticed. Thus, the term ‘bronze’ for the binary CueSn alloys is literally correct for most of the artifacts under consideration. There are some outliers present including six objects whose tin content is 2% or less. It is significant to note that five of them were recovered from a single site, Khairwada, with three of the items being small rings (objects #3e5). No such rings from the other four sites mentioned in this study were available for examination. For this reason, it is not yet clear if this low-tin phenomenon was unique to this specific site or if it was simply limited to the objects in question. It is true, however, that the artifacts from Khairwada generally contain less tin than those from the other sites. As an example, object# 7, a dish with a lid retrieved from Khairwada, is notable in this respect and is the only example of the many domestic items examined that was made of almost pure copper. Since an increase in tin content can strengthen bronze, adding more tin is therefore desirable if greater strength is required. However, if the tin level exceeds 10%, the resultant bronze may become fragile due to precipitation of the brittle d phase. It is possible to suppress the formation of this phase for tin levels over this amount, though doing so is difficult to achieve in practice. As such, a specific tin concentration near 10% is preferred when mechanical working is anticipated during fabrication, especially when improved strength is critical to the final product. For bronze objects in thin sheet forms such as those shown in Fig. 2, the two competing requirements of strength and ductility (i.e., the ease of plastic deformation) should be met simultaneously. Likewise, the presence of lead must be controlled and minimized given its potentially catastrophic effects on the end product. Thus, it is vital that specific lead-free alloys of near 10% tin content be consistently selected. Careful recognition and application of these conditions would, therefore, suggest an understanding of the physical properties involved as determined by the compositions of the materials and the thermo-mechanical treatments used. For the assembly under review, dominance of sheet metal items such as those in Fig. 2 indicates that tin, and even copper, was not readily available to most people. The strictness in selecting near 10% tin content, optimal for reducing wall-thickness without sacrificing load-bearing capacity, is also characteristic of an effort to minimize consumption of valued materials. In this respect, the use of considerably more tin in objects #33 and 48 is rather exceptional. The extra cost, however, would have been more than compensated for if the increased tin level enabled similar items to be made with much less material. According to Park et al. (2009), high-tin alloys, through the proper control of thermal treatments and tin levels, can be sufficiently hardened for use in thin-walled functional items. They showed that the best result can be attained when alloys of near peritectic composition (22% Sn) are quenched at around 700 C. In Korea, for example, where access to tin was limited, this particular technology was applied for more than a millennium to
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produce various high-tin objects with walls as thin as a few tenths of a millimeter (Park and Gordon, 2007). By contrast, the tin fraction and heat-treating temperatures inferred from objects #33 and 48 appear to deviate substantially from the optimal conditions mentioned above, thereby suggesting that such technology may not yet have been fully established at that particular megalithic site. Arsenic in copper can lower the liquidus temperature and facilitate casting. In as-cast conditions though, its effect on hardening is virtually insignificant (Lechtman, 1996). In mechanical working, however, arsenic can be just as effective as tin for ensuring product strength and ductility. It is also particularly advantageous in the fabrication of thin plates. The best historical example of this effect being explored can be found in pre-industrial Andean South America where arsenical copper was widely used in the production of sheet metal objects (Burger and Gordon, 1998; Lechtman, 1996). It should be noted that although the bronze assemblage in Fig. 2 consists mostly of sheet metal products, this study found no evidence of arsenic addition being applied for this particular purpose. The paucity of arsenical copper was also noted in the two Indus sites at Lothal and Rangpur in Western India (Kenoyer and Miller, 1999). By contrast, arsenic was frequently used in other Indus sites such as Mohenjo-daro and Harappa in Pakistan. The use of lead in bronze has the effect of lowering melting temperatures and improving flow characteristics, two key properties required in casting operations. It is also beneficial in reducing the amount of costly materials needed such as tin and copper. Yet, despite these advantages, this study found no added lead in the three bells that were cast (objects #6, 26 and 49). Instead, the craftsman, perhaps taking into account the added geometrical complexity of the design, raised the tin level only for object #26, which was cast as a single piece as opposed to the others consisting of two pieces cast separately before being assembled. In a tinlacking environment, the use of expensive tin where cheap lead could have been used just as effectively suggests that copper and related alloys were likely recycled. This would coincide with similar practices widely used in India from the Indus period (Kenoyer and Miller, 1999: 115). Since lead is not tolerated in sheet metal products, lead-contaminated objects cannot be recycled for use in such applications. Thus, extreme care must be taken to prevent further contamination during recycling when mixing lead-based and leadfree scraps. Unfortunately, doing so would have been nearly impossible to achieve in practice. Subsequently, the complete absence of lead intended in any of the specimens examined suggests that a rule or guideline was put in place by these craftsmen to avoid undesirable lead corruption. This rule would likely have not been respected without strict cooperation from among the megalithic communities involved who shared a common exchange network for bronze based products and technology. Since lead was widely used in Indus sites, both as a separate metal and as an alloying element in bronze (Kenoyer and Miller, 1999: 119), it is unlikely that the absence of lead in the bronze objects under review was associated with the availability of raw materials. Table 1 lists nine bangles (#1, 9, 10, 23e25, and 44e46) with a tin content averaging 8.7%. Their load-bearing capacity would not have been a critical factor in determining which materials to use, and even non-alloyed copper would have been strong enough for their intended purpose as an ornament. In fact, of the five bangles from the Indus site at Lothal as reported by Kenoyer and Miller (1999), three were made with copper bearing no deliberate alloying. With regards to the presence of tin in all of the bangles we examined, as with the other functional items, this was likely not meant for strength. Instead, the addition of tin may have been intended to improve color characteristics. If color, therefore, was the only or primary criterion that mattered, improved strength from tin alloying may have allowed a substantial amount of lead to
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be added without any noticeable color change. Doing so would then have allowed expensive tin and copper to be saved. Such lead addition, however, would have prevented these objects from being recycled as sheet metal products for the duration of their use. It should be noted that if bronze ornaments such as bangles remain lead-free, they can readily be forged into practical items. However, without tin addition, they cannot be used until their tin level is raised. This treatment involves melting the product, which presents technological complications and substantial material loss. Another fact to be noted of the bangles in Table 1 is that they were all given a thorough thermo-mechanical treatment after casting. Their microstructures were well annealed and nearly free of any defects such as cavity porosities and brittle d particles. This additional treatment is not required if they are to be used as an ornament. It is necessary, however, if they are to be used as a feedstock for further processing by forging. It is evident, therefore, that the bangles were not produced exclusively for ornamental purposes and, given their well-controlled chemical compositions and microstructures, represent items also used for trade. Such intermediary products could have been forged into other useful items at a later date, thereby meeting a wider range of consumer needs. Moreover, their production and circulation, as a great innovation tailored to suit the unique needs of the megalithic bronze industry, would have given rise to greater freedom and flexibility for both producers and consumers alike. The idea of circulating such pre-alloyed intermediaries ready to be forged into finished items would be even more practical if the raw materials, copper and tin, were not available nearby. Little is known of their sources for the megalithic sites under consideration. According to the data collected by Kenoyer and Miller (1999: 117e118), however, copper smelting slags dated to the early second millennium BC were reported in Rajasthan while Afghanistan was suggested as a likely tin source for Indus sites. The largest tin deposits in the subcontinent were reported in Bihar, but their exploitation began quite recently (Penhallurick, 1986:21). 5. Conclusion Bronze objects recovered from five megalithic sites in the Vidarbha region of India were examined for their alloy compositions and microstructures. The assembly consisted primarily of sheet metal products along with some bangles and small bells. The analytical results showed that the technology involved can be characterized by an extreme dependence on forging during fabrication and a consistent selection of CueSn alloys of near 10% tin. This technological status represents a fully developed bronze tradition optimized and dedicated to the production of thin-walled objects such as those under investigation. In sheet metal technology, lead contamination is detrimental to the material properties of a given bronze object and should, therefore, be avoided if recycling is intended. In the specimens examined, no lead addition was detected. This indicates that a ban on adding lead may have not only been in place but also well respected by the megalithic members of this particular bronze tradition. In addition, the absence of lead in even non-sheet metal products such as bangles and bells, where it would have been highly desirable, suggests that recycling was also an important factor in material selection and product composition. This hypothesis is further supported by the presence of a high tin content which would not have been necessary for the items in their current form, but would have been highly advantageous if the products were to be used as intermediaries and later forged into other functional items. It is not clear how this particular megalithic bronze technology evolved or how it relates to the Indus tradition. One possibility is that, after the decline of the Indus Civilization, it was carried
forward by the indigenous survivors until the onset of the local Iron Age. The key features found in most Indus bronze objects, namely limited tin and negligible lead, suggest that the alloys were primarily made for use in forging rather than casting. These nonoptimized (tin-deficient) alloys likely reflect a restriction in material resources as opposed to a lack of technological sophistication. In this respect, the megalithic and Indus traditions are not so much different as to deny a plausible connection. In the megalithic communities, such a unique bronze tradition dedicated to sheet metal technology may have been a practical choice to take advantage of the changing role of bronze as dictated by the introduction of iron. In sheet metal products, the selection of specific CueSn alloys, with near 10% tin and without lead, is critical to ensuring that strict material properties be maintained. For this reason, the use of more tin was an optimal way to minimize material costs while protecting product integrity. Also, the dominance of thinwalled bronze items, indicative of a resource-limited environment, suggests that both tin and copper were regarded as expensive commodities. As the excavation report for the site at Raipur (Deglurkar and Lad, 1992) showed, the bronze objects recovered mostly came from burials of apparently high-status people. Iron artifacts, by contrast, were given no such distinction. Thus, for the megalithic communities of the Vidarbha region, bronze may have in fact become a more prestigious material, one readily available only for elites who could afford it. This would suggest that a more rigid socio-economic stratification appeared following the introduction of iron technology. As previously mentioned, the megalithic bronze tradition under consideration is uniquely defined by a consistent selection of specific alloys, a perfect control of lead contamination, and an innovative use of ornamental items as multi-purpose intermediaries. These characteristics reflect a high level of standardized technological achievement and testify to the collaborative efforts of the participating communities. Allchin and Allchin (1982: 335), from their typological study on megalithic iron artifacts, proposed that a group of traveling metalworkers disseminated similar technologies across the megalithic landscape of South India, from Nagpur in the north to Adichanallur in the south. The high level of standardization and collaboration, evident in the bronze objects examined, suggests that this theory may be true at least within the Vidarbha region. Continuation of this study is, therefore, recommended to determine if this theory can apply to other megalithic sites in the area and beyond.
Acknowledgments Our work would not have been possible without the kind support from Dr. James Lankton. Thanks are also due to the people of Deccan College who showed hospitality to one of the authors (JSP) when he visited Pune with his wife to take samples for examination. Dr. Jamkhedkar is acknowledged for his encouragement of this work. This project was financially supported by the Korea National Research Foundation (NRF-2012-0029808).
References Allchin, B., Allchin, R., 1982. The Rise of Civilization in India and Pakistan. Cambridge University Press, Cambridge. Burger, R.L., Gordon, R.B., 1998. Early Central Andean metalworking from Mina Perdia, Peru. Science 282, 1108e1111. Craddock, P.T., 1979. The copper alloys of the Medieval Islamic World e inheritors of the classical tradition. World Archaeology 11.1, 68e79. Deglurkar, G.B., Lad, G.P., 1992. Megalithic Raipur (1985e1990). The Deccan College Post-graduate and Research Institute, Pune India. Kenoyer, J.M., Miller, H.M.-L., 1999. Metal technologies of the Indus Valley tradition in Pakistan and Western India. In: Pigott, V. (Ed.), The Archaeometallurgy of the
J.-S. Park, V. Shinde / Journal of Archaeological Science 40 (2013) 3811e3821 Asian Old World, MASCA Research Papers in Science and Archaeology, vol. 16. University Museum Monograph 89, Philadelphia, pp. 5e151. Lechtman, H., 1996. Arsenic bronze: dirty copper or chosen alloy? A view from the Americas. Journal of Field Archaeology 23, 477e514. Park, J.S., Gordon, R.B., 2007. Traditions and transitions in Korean bronze technology. Journal of Archaeological Science 34, 1991e2002. Park, J.S., Park, C.W., Lee, K.J., 2009. Implication of peritectic composition in historical high-tin bronze metallurgy. Materials Characterization 60, 1268e 1275. Park, J.S., Shinde, V., 2013. Iron technology of the ancient megalithic communities in the Vidarbha region of India. Journal of Archaeological Science 40 (11), 3822e3833.
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Penhallurick, R.D., 1986. Tin in Antiquity-its Mining and Trade Throughout the Ancient World with Particular Reference to Cornwall. The Institute of Metals, London. Possehl, G.L., Gullapalli, P., 1999. The early Iron Age in South Asia. In: Pigott, V. (Ed.), The Archaeometallurgy of the Asian Old World, MASCA Research Papers in Science and Archaeology, vol. 16. University Museum Monograph 89, Philadelphia, pp. 153e175. Srinivasan, S., July 1998. The use of tin and bronze in prehistoric southern Indian metallurgy. JOM, 44e50. Thakuria, T., 2010. The Society and Economy During Early Iron Age and Early Historic Period in Deccan with Special Reference to Beads (1000 BC to 500 AD) (Ph. D thesis). The Deccan College Post-graduate and Research Institute, Pune, India.
Contents lists available at SciVerse ScienceDirect
Journal of Archaeological Science journal homepage: http://www.elsevier.com/locate/jas
Bronze technology of the ancient megalithic communities in the Vidarbha region of India Jang-Sik Park a, *, Vasant Shinde b,1 a b
Department of Metallurgical Engineering, Hongik University, 2639, Sejong-ro, Jochiwon-eup, Sejong 339-701, Republic of Korea Deccan College, Post-Graduate & Research Institute, Deemed University, Pune 411006, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 July 2012 Received in revised form 21 May 2013 Accepted 25 May 2013
Metallographic examination was carried out on forty-nine copper and bronze objects from five megalithic sites located in Vidarbha, India. The artifact assembly consists of horse ornaments, kitchenware, bangles, rings, small bells and the hilt of an iron dagger. Results show that the technology involved is characterized by the use of bronze alloys containing approximately 10% tin based on weight and the application of forging as a key method of fabrication. No deliberate addition of lead was observed. Arsenic was detected, but very rarely and only as an insignificant minor element. The consistent selection of such specific alloys indicates that the megalithic communities in this particular region had established a fully developed and standardized bronze tradition optimized for the production of forged items. Their advanced technological status was also noted in a special technique applied to two forged high-tin bronze bowls. Such a unique bronze tradition, dedicated to sheet metal technology, was most likely a practical choice made by these people to take advantage of the changing role of bronze. Specifically, with the introduction of iron, bronze seems to have become a more prestigious material that could serve as an indicator of the appearance of a more rigid socio-economic stratification within the megalithic communities of the Vidarbha region. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: India Megalithic period Bronze technology Chemical composition Microstructure
1. Introduction The megalithic period in India, which began approximately in the early first millennium BC, is notable for the emergence of iron metallurgy and new burials, referred to as megaliths. In a companion article (Park and Shinde, 2013), our team examined iron objects from five megalithic sites located in the Vidarbha region of the Maharashtra state (Fig. 1). The result showed that these megalithic communities shared a fully developed and wellstandardized iron technology of substantial flexibility. In this paper, we focus on the bronze objects excavated from the same megalithic sites and characterize the technology applied in their fabrication. The sites were all closely located and dated to the first half of the first millennium BC based on typological grounds (Thakuria, 2010: 67e73). This chronology is in fair agreement with the radiocarbon age of one of the sites at Bhagimohari as reported in the data set compiled by Possehl and Gullapalli (1999). Their
* Corresponding author. Tel.: þ82 44 860 2562; fax: þ82 44 866 8493. E-mail addresses: [email protected], [email protected] (J.-S. Park), [email protected] (V. Shinde). 1 Tel./fax: þ91 20 26513203. 0305-4403/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jas.2013.05.030
intimate relationship was also confirmed in the external appearance and purpose of iron and bronze objects excavated. The iron objects from them were mostly for tools and weapons while the bronze objects consisted primarily of ornaments and kitchenware. More information on the archaeological context of the sites and findings may be found in the companion article mentioned above. Bronze making begins with a determination of the alloying elements and the amounts needed to meet certain material properties required for fabrication and use. In antiquity, tin (Sn), arsenic (As) and lead (Pb) served as the major elements that could be deliberately added to copper (Cu). The presence of these elements in copper lowers the melting temperature and improves the flow property of the molten alloys. This helps to facilitate the process of casting. In addition, tin and arsenic aid in the strengthening of the alloys, thereby allowing objects of a similar purpose to be made with less material. It should be noted that adding lead may lower material costs and promote better casting, but it may also sacrifice the impact resistance and the load-bearing capacity of the end product. Bronze objects can be fabricated either exclusively through casting or by a more complex process involving substantial forging once initial casting has been completed. In the latter case, forging is the primary method for shaping the material, during which
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was established in the megalithic communities of South India. Her major concern, however, dealt with the use of high-tin bronze, and it is not clear if her results can accurately represent the general bronze traditions practiced in the region at that time. The data compiled by Kenoyer and Miller on the chemistry of Indus objects constitute a rare reference for comparative studies in ancient Indian bronze technology. Their data show that of the Indus objects examined copper alloys with added tin occupy less than 30% of the assemblage. In addition, and more importantly, tin levels were found to vary substantially. Lead was added only in certain exceptional cases. 2. Comments on artifacts
Fig. 1. Map of India. (a) The Indian subcontinent with the city of Nagpur indicated by the arrow; (b) the state of Maharashtra with the city of Nagpur marked by the asterisk within the shaded region of Vidarbha. Spots 1e5 denote the sites at Borgaon, Khairwada, Bhagimohari, Mahurjhari and Raipur, respectively, from which the bronze objects under review were recovered.
noticeable strengthening can also occur. It is important to note that the method of fabrication must be carefully selected with the chemical composition of the alloys in mind. The process of combining alloy compositions with proper fabrication techniques can lead to the establishment of a bronze technology, one that will reflect the availability of resources, the cultural traditions, and the technological advancements of its practitioners. Thus, the characterization of an established bronze tradition may provide further insight into the socio-cultural environment and influential trade networks of a given community. Unfortunately, bronze objects of Indian megalithic communities have not yet been thoroughly explored as valuable archaeological materials bearing important information on megalithic culture. In fact, megalithic bronze tradition has drawn only marginal attention, and not much is known of the technological aspects characterizing this tradition in comparison to that of other communities with varying regional or chronological contexts. In this respect, the research conducted by Srinivasan (1998) and by Kenoyer and Miller (1999) serves as a useful source of information. According to Srinivasan, a highly sophisticated bronze technology
Fig. 2 shows the general appearance of the forty-nine bronze objects examined, all of which are currently on display in the megalithic room of the Deccan College Museum. The assembly consists of ten bangles (objects #1, 5, 9, 10, 23e25 and 44e46), an ornament (#2), two rings (#3 and 4), three bells (#6, 26 and 49), six dishes (#7, 8, 30, 32, 33 and 48), nineteen horse ornaments (#11e22 and 37e43), six bowls (#27e29, 31, 34 and 36), the hilt of an iron dagger (#35) and a pot (#47). The artifacts were recovered through controlled excavations at five megalithic sites (see Fig. 1) in the Nagpur district of the Maharashtra state. Two objects (#1 and 2) are from Borgaon, six objects (#3e8) are from Khairwada, two objects (#9 and 10) are from Bhagimohari, twenty-nine objects (#11e36 and 47e49) are from Mahurjhari, and ten objects (#37e46) are from Raipur. The bar near each object in Fig. 2 corresponds to 1 cm unless otherwise noted. Brief information about the usage and recovery site of each object is provided in Table 1. The artifact numbers are consistent between Fig. 2 and Table 1, and lower case letters have been used to differentiate individual parts of a given object containing multiple pieces. For cases involving two or more specimens taken from a single piece, their locations are marked in the object by arrows a1, a2 and a3. It should also be mentioned that objects #39c and 39d are almost identical in shape and size to #14 and 15, and are displayed in #39 as the components of one artifact. Visual inspection of the assemblage under investigation revealed several significant facts. First, the objects were mostly fabricated from thin metal sheets; however, the three bells and ten bangles are notable exceptions. The bells were intended for horse ornaments and are generally similar in shape and size. Two of them (#6 and 49) contain two parts assembled near the shoulder while the other bell (#26) consists of one single piece. Second, the assemblage can be classified into two distinct groups, one consisting of ornaments for either humans or horses and the other containing domestic items such as bowls and dishes. Third, the assemblage has no tools or weapons. It should be noted that with regard to object #35 the item is merely a hilt, not the iron dagger itself, and is therefore not much different from an ornament. 3. Laboratory examination and results Small specimens were taken from the objects and then mounted, polished and etched with a solution of 100 ml methyl alcohol, 30 ml hydrochloric acid and 10 g ferric chloride. Their microstructures were examined using an optical microscope and a scanning electron microscope (SEM). The alloy composition was measured using the energy dispersive x-ray spectrometer (EDS) included with the SEM instrument. This information is reported in Table 1 according to weight fraction. The tin level is given to the nearest whole digit. For the other minor alloying elements (i.e., sulfur, iron, lead and arsenic), their levels are provided to within 0.5%, even though the EDS instrumentation is capable of providing
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Fig. 2. General appearance of the bronze objects examined. Objects #1 and 2 are from Borgaon; #3e8 are from Khairwada; #9 and 10 are from Bhagimohari; #11e36 are from Mahurjhari; #37e46 are from Raipur; and #47e49 are from Mahurjhari. The objects consist of 10 bangles (objects #1, 5, 9, 10, 23e25 and 44e46), an ornament (#2), 2 rings (3 and 4), 3 bells (#6, 26 and 49), 6 dishes (#7, 8, 30, 32, 33 and 48), 19 horse ornaments (#11e22 and 37e43), 6 bowls (#27e29, 31, 34 and 36), the hilt of an iron dagger (#35) and a pot (#47). The bar near each object corresponds to 1 cm unless otherwise noted. The numbers labeling the objects are consistent with those in Table 1. The lower case letters used distinguish multiple parts of an object. The labels a1 and a2 denote the locations from which two specimens were taken from a single part of an object.
accuracy readings to within a few tenths of a percent. The average composition of each specimen was inferred from the EDS spectrum taken in a raster mode. In general, the area of each specimen was approximately 0.65 0.45 mm, except in cases where restrictions on the specimen size necessitated a smaller sample.
3.1. Microstructure Fig. 3aef show optical micrographs of the structures of objects #12a, 39c, 39b, 40, 27 and 18, respectively. These structures consist primarily of the a phase in the CueSn system. The a grains are seen
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Table 1 Summary information, including chemical compositions, for the bronze objects examined from megalithic sites at Nagpur in the Maharashtra province of India. The numbers labeling the objects are consistent with those in Fig. 2. Artifact # (# in Fig. 2)
Description of artifact (largest dimension in cm)
Site
1 2 3 4 5 6 7
Bangle (7.2) Ornament [rod with a bulged end] (2.5) Ring (2.1) Ring (2.3) Ring (5.6) Horse ornament [Bell] (10.0) Dish with a lid (8.4) Rim Wall Lid Dish with a lid (5.1) Rim Wall Lid Small bangle (3.9) Bangle (8.4) Horse ornament cut from a plate (24.0) Horse ornament (7.8) Rod rolled from a sheet Crescent cut from a sheet Horse ornament (9.5) Rod rolled from a sheet Shape cut from a sheet Hollow hemisphere with a little rod attached across the bottom (2.5; 2.1) Horse ornament cut from a plate (10.2) Horse ornament (7.3) Edge of the object rolled into a rod Main body cut from a sheet Circular horse ornament with a domed center (6.0) Circular horse ornament with a conical center (7.1) Circular horse ornament with a domed center (6.0) Circular horse ornament with a conical center (6.0) Circular horse ornament with a conical center (7.2) Bangle (10.1) Bangle (6.6) Bangle (5.5) Horse ornament [Bell] (10.5) Bowl (15.5) Bowl (12.0) Bowl (12.5) Dish (26.0) Rim Bottom Bowl (17.0) Dish (14.0) Dish (13.5) Bowl (18.0) Hilt of an iron dagger (9.0) Bowl [Bone inside] (14.2) Horse ornament in the form of a rectangular rod rolled from a sheet (13.1) Horse ornament cut from a sheet (9.1) Horse ornament (25.0) Rectangular rod with ringed ends and attached to the bottom of#39b Main body cut from a plate Hollow hemisphere with a little rod attached across the bottom (similar to #14 and 15) Horse ornament cut from a sheet (9.6) Horse ornament (13.3) Rod rolled from a sheet Main body cut from a sheet Circular horse ornament with a conical center (7.9) Horse ornament cut from a plate (8.2) Bangle (6.0) Bangle (6.0) Bangle (5.3) Pot (19.0) Rim Wall Bottom Dish on an 11-legged stand (11.5) Horse ornament [Bell] (10.0)
Borgaon
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
a1 a2 b a1 a2 b
a b a b
a1 a2
a1 a2
31 32 33 34 35 36 37 38 39
a
b c d 40 41 42 43 44 45 46 47
48 49
a b
a1 a2 a3
Composition (wt.%) Sn
e none detected; tr trace amount.
Khairwada
Bhagimohari Mahurjhari
Raipur
Mahurjhari
Fabrication method
S
Fe
Pb
As
7
0.5
e
e
e
1 e 2 6 1 1 1 9 8 8 8 11 6 10 9 9 8 10 9 11 12 12 11 11 11 8 12 9 8 9 12 9 10 6 9 10 8 6 17 10 10 9 11
0.5 0.5 1.0 1.0 e 0.5 e e e e 0.5 e 1.0 e e tr tr 0.5 tr 0.5 0.5 0.5 e 0.5 e 1.5 0.5 e 0.5 0.5 tr 1.5 0.5 0.5 0.5 0.5 0.5 e e tr 0.5 tr 0.5
e e e 0.5 tr 0.5 1.0 1.0 0.5 0.5 e e 1.0 e e 0.5 0.5 0.5 e e e e e e e 1.5 e e 0.5 1.0 0.5 e 0.5 0.5 0.5 0.5 0.5 0.5 tr 0.5 tr 0.5 0.5
e e e 0.5 e e e tr tr e tr e e e tr e e e e e e e e tr e e e e e e tr e e tr e e e 0.5 e e e e 1.0
e e e e e e e e e e e e e e e e e e e e e e e e e e e 5.0 e e e e e 1.5 e e e 1.5 e 1.0 e e e
Forged Cast Forged Forged Forged Cast Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Cast Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged
11 1
0.5 e
0.5 0.5
1.0 tr
e e
Forged Forged
9 9 9
0.5 e e
1.0 e e
e e e
e e e
Forged Forged Forged
10 8 9 8 10 9 9 8 10 10 9 18 6
e tr e e e 0.5 0.5 tr 0.5 0.5 0.5 0.5 e
e 0.5 e 0.5 e e tr tr 1.0 1.0 0.5 e e
1.00 e e e e e e e e e e e tr
e e e e e e e 0.5 e e e e e
Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Forged Cast
Comments
Corroded; a-dendrite
Trace Bi
Trace delta phase Trace delta phase
Trace delta phase
b-Martensite phase
Retained g-phase
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Fig. 3. Optical micrographs. (a)e(f) Microstructures of specimens taken from objects #12a (horse ornament), 39c (horse ornament), 39b (horse ornament), 40 (horse ornament), 27 (bowl) and 18 (horse ornament) in Fig. 2, respectively.
to contain straight twin boundaries, indicating that the objects were more or less subjected to plastic deformation during fabrication. The dark particles or ribbons scattered over the bright a background correspond to non-metallic inclusions of copper sulfide. Their density was determined during the copper smelting process and was influenced by the character of the ores used. Their shape, however, was decided during fabrication, and the sulfides were elongated to such an extent as to form continuous horizontal layers as seen in Fig. 3e. These conditions reflect the extreme degree of forging applied to object #27. The low density of twins in Fig. 3b, along with less deformed inclusions, demonstrates that object #39c was given minimal forging. A similar microstructure was also observed in objects #11, 12 and 39d, which are almost identical in shape to object #39c. Furthermore, the microstructure in Fig. 3f is unique in that it has a small a-d eutectoid located in the dark irregular regions. Fig. 4aed present typical results obtained from the SEM analyses. Fig. 4a, an EDS spectrum from the entire area of Fig. 3c, shows the presence of major elements, copper (Cu) and tin (Sn), along with other minor elements, sulfur (S) and iron (Fe). The carbon (C)
peak in this spectrum, as well as in those that follow, is due to the thin carbon coating applied for the purpose of this SEM examination, and can be ignored. The approximate average composition of the specimen as inferred from Fig. 4a is 9% Sn, 0.5% S, and 1.0% Fe plus balance copper. Here, tin is the only element that was added intentionally during alloy making. By contrast, sulfur and iron were included inadvertently. Fig. 4b, an EDS spectrum from one of the inclusions marked by the arrow in Fig. 3c, shows the inclusion to be a particle of copper sulfide containing a substantial amount of iron and a slight amount of selenium (Se). Fig. 4a and b represent the EDS spectra obtained from the majority of the objects examined, with only minor variations detected in a relative fraction of the elements present. One notable exception found was that certain specimens contained lead (Pb) in a trace amount. These lead particles were more easily identified using the SEM micrographs than the optical micrographs as seen in Fig. 4c, an SEM micrograph magnifying the area near the arrow in Fig. 3d. Fig. 4c shows bright particles of almost pure lead formed during solidification due to the limited solubility of the material in solid copper. Fig. 4d, an EDS spectrum taken from one of the lead particles marked by
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Fig. 4. EDS spectra and SEM micrograph. (a) EDS spectrum taken from the entire area shown in Fig. 3c; (b) EDS spectrum taken from the arrow in Fig. 3c; (c) SEM micrograph enlarging the area marked by the arrow in Fig. 3d; (d) EDS spectrum taken from the arrow in (c).
the arrow in Fig. 4c, shows that the major constituent is lead. The presence of chlorine (Cl) resulted from the applied etching solution which contained this element as a constituent. It is, therefore, irrelevant to the particle’s original composition and can be disregarded. The analytical results from most of the objects examined were fairly consistent and well represented by the micrographs and EDS spectra presented in Figs. 3aef and 4aed. There were, however, notable exceptions where different alloys were used. In some cases, different thermo-mechanical treatments were applied as well during fabrication. Fig. 5aef, optical micrographs of the specimens from objects #3, 23, 33, 48, 6 and 26, respectively, illustrate the varying microstructures produced when alloy compositions and thermo-mechanical treatments differed. The results in Fig. 5a closely resemble those of the previous optical micrographs where elongated sulfide inclusions were scattered over the twinned a background. The EDS analysis, however, showed the tin content to be approximately 1%, which is too small to be considered a result of intended alloying. The structures presented in Fig. 5bed are exceptional in that they do not consist of a single a phase but rather contain minor second phases. Formation of the latter, reflecting an increase in the level of alloying elements, is the most likely explanation of the visible contrasts seen in these particular micrographs. Specifically, in Fig. 5b, the presence of 5% arsenic and 9% tin was responsible for the formation of a second phase in the bright areas scattered over the darker a background.
By contrast, the second phases in Fig. 5c and d correspond to bmartensite and retained g, respectively. Such results would be expected in high-tin bronze alloys with a tin content approaching or exceeding 15%. Moreover, this type of second phases would not be expected to form during slow cooling; rather, it would be obtained only after quenching. For this sample, the presence of bmartensite indicates that the specimen was quenched at or above 600 C while the retained g phase suggests that quenching was performed at a temperature between 520 C and 586 C. It is also important to note that for Fig. 5c and d the average tin level measured was 17% and 18%, respectively, with no other alloying elements detected. For Fig. 5e and f, the structural characteristics determined during the solidification reaction were more or less retained without any evidence of thermo-mechanical treatments being applied after casting. It is evident, therefore, that objects #6 and 26 (two bells), as seen in Fig. 2, were fabricated exclusively through casting. The tin levels were found to be approximately 6% in Figs. 5e and 12% in Fig. 5f. Of particular importance are the large dark areas in Fig. 5f. These represent shrinkage cavities due to volume contraction during freezing. Their presence in this higher tin object (#26) is likely associated with the fact that it was cast from a single piece while the lower tin object (#6) was made of two separately cast pieces that were later assembled together. The increased tin content apparently, however, did not compensate for the difficulties arising from the complex geometry to be cast.
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Fig. 5. Optical micrographs. (a)e(f) Microstructures of specimens taken from objects #3 (ring), 23 (bangle), 33 (dish), 48 (dish with a stand), 6 (bell) and 26 (bell) in Fig. 2, respectively.
Fig. 6aed show the results of the SEM analyses on the second phase areas observed in Fig. 5b and d. Fig. 6a, an SEM micrograph enlarging the area marked by the arrow in Fig. 5b, depicts a twophase region present in the a background. Fig. 6b, an EDS spectrum of the entire area of Fig. 5b, shows this specimen to contain both tin and arsenic as alloying elements. The average tin and arsenic levels inferred from Fig. 6b were approximately 9% and 5%, respectively. The EDS analyses for arrows 1e4 in Fig. 6a show that the approximate alloy contents at each arrow correspond to 11% Sn6% As, 12% Sn-7% As, 16% Sn-7% As and 29% Sn-3% As, respectively. These results indicate that the two-phase region was caused by a eutectic reaction between the a (arrow 3) and d (arrow 4) phases of the ternary CueSneAs system. This reaction was made possible by a solute enrichment brought on by elemental segregation during solidification. Thus, the increase in tin and arsenic levels from arrows 1 to 2 suggests that both elements were enriched toward the two-phase region as solidification progressed. Fig. 6c, an SEM micrograph magnifying the area marked by the arrow in Fig. 5d, shows the presence of another second phase, g, along with the major phase, a. The tin content of this g phase is
approximately 27%, as inferred from Fig. 6d, an EDS spectrum taken from the arrow marking one of the g areas. It is important to note that the g phase becomes unstable below 520 C and undergoes eutectoid phase transformation between the a and d phases of the binary CueSn system. Thus, since the g phase was retained in this particular specimen, it is apparent that the artifact examined underwent a special thermal treatment similar to the one described above. 3.2. Chemical composition Table 1 summarizes the chemical composition of the forty-nine objects examined. Some of them (#7, 8, 12, 13, 39 and 41) represent an assemblage of two or more separate parts, each of which produced an individual specimen. For objects #7, 8, 17, 30 and 47, more than one sample was taken from each object or part. The elemental distribution, as observed in the multiple specimens taken from the single samples (#7a1-a2, 8a1-a2, 17a1-a2 and 43a1-a3), is relatively uniform as noted in Table 1. This suggests that the composition data represent the objects under investigation.
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Fig. 6. SEM micrographs and EDS spectra. (a) SEM micrograph magnifying the area marked by the arrow in Fig. 5b; (b) EDS spectrum from the entire area of Fig. 5b; (c) SEM micrograph magnifying the area marked by the arrow in Fig. 5d; (d) EDS spectra from the arrow in (c).
Table 1 shows that the majority of the specimens listed contain tin as a major alloying element, along with several minor constituents such as sulfur, iron, lead and arsenic. Sulfur and iron, present in a number of specimens, presumably were added inadvertently during smelting. It is important to note, however, that the sulfur detected was a constituent of copper sulfide inclusions which were often iron-contaminated. By contrast, the iron existed as a solute element in the metallic a phase. Lead was also detected in some specimens, though only at a fraction of 1% or below. This indicates that it was not intended but rather added inadvertently by the use of lead-contaminated ores in smelting (Craddock, 1979). One may, therefore, assume that the presence of sulfur, iron and lead is completely fortuitous. In addition, since these elements appeared in such small amounts, their effects on the material properties of the objects in question would have been minimal, at best, meaning they probably would have gone unnoticed. As for the presence of arsenic, this element was added, most likely during the smelting process through the use of specific ores. In this case, noticeable effects on alloy properties would have been observable when its fraction exceeded 1%. Given these conditions, it is apparent that tin and arsenic were the only alloying elements intended. The specimens in Table 1 can be classified into three groups based on their tin levels. First, objects #3e5, 7a1, 7a2, 7b and 39a constitute a low-tin group where each member contains 2% tin or less. Second, objects #33 and 48, with 17% and 18% tin respectively, represent a high-tin group. Third, all other objects belong to a group where the tin level ranges from 6% to 12%. It should be noted that
for the last group the tin content generally falls within a narrow window of 8%e12%, with the six exceptions being objects #1, 6, 11, 29, 32 and 49. For objects in the first group, a tin level below 2% is too small to be considered intended. Thus, members of the low-tin group are herein referred to as copper objects while the term bronze is reserved for members of the higher-tin groups only. Table 1 lists four objects (#23, 29, 32 and 34) in which arsenic is present. All of them contain 6%e10% tin with arsenic detected as a minor alloying element. It is important to note that in two cases (#29 and 32) the specimens contain 6% tin. This tin level is the lowest of the group they belong to and departs significantly from the average composition of the group. In general, arsenic addition in copper, which usually takes place during smelting, not only lowers the melting temperatures but also promotes work hardening (Lechtman, 1996). As such, the reduced tin concentration in the two objects above may not be fortuitous, but was likely associated with the presence of 1.5% arsenic in both. Table 1 contains only four objects (#2, 6, 26 and 49) that were shaped through casting without forging. For object #2, the specimen was severely corroded and its composition could not be determined accurately. Evidence, however, from EDS and microstructure analyses showed it to contain a substantial amount of tin. For objects #6 and 49 (two of the three cast bells), the tin content was determined to be 6%. It should be mentioned that in virtually every specimen examined in the bronze groups, the tin fraction was controlled to a range of 8%e12%, with notable exceptions being the cast objects #6 and 49 and the arsenic-added objects #29 and 32.
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4. Discussion The results in Table 1 show that the bronze tradition of the five megalithic communities in Vidarbha was established consistently on the basis of forging as a primary means of fabrication and the use of CueSn alloys of near 10% tin content as major materials. This consistency in technological aspects is in agreement with the prediction based on artifact typology. All except four of the objects examined were fabricated through forging, mostly in the form of thin sheets. Approximately 90% of the objects were made of bronze alloys with 6% tin or greater, predominantly with tin levels between 8% and 12%. Arsenic was also added, but only in four of the objects under review and as a minor constituent in supplementing tin. Other elements such as sulfur, iron and lead were detected in a number of specimens, but only in trace amounts such that their presence may have gone unnoticed. Thus, the term ‘bronze’ for the binary CueSn alloys is literally correct for most of the artifacts under consideration. There are some outliers present including six objects whose tin content is 2% or less. It is significant to note that five of them were recovered from a single site, Khairwada, with three of the items being small rings (objects #3e5). No such rings from the other four sites mentioned in this study were available for examination. For this reason, it is not yet clear if this low-tin phenomenon was unique to this specific site or if it was simply limited to the objects in question. It is true, however, that the artifacts from Khairwada generally contain less tin than those from the other sites. As an example, object# 7, a dish with a lid retrieved from Khairwada, is notable in this respect and is the only example of the many domestic items examined that was made of almost pure copper. Since an increase in tin content can strengthen bronze, adding more tin is therefore desirable if greater strength is required. However, if the tin level exceeds 10%, the resultant bronze may become fragile due to precipitation of the brittle d phase. It is possible to suppress the formation of this phase for tin levels over this amount, though doing so is difficult to achieve in practice. As such, a specific tin concentration near 10% is preferred when mechanical working is anticipated during fabrication, especially when improved strength is critical to the final product. For bronze objects in thin sheet forms such as those shown in Fig. 2, the two competing requirements of strength and ductility (i.e., the ease of plastic deformation) should be met simultaneously. Likewise, the presence of lead must be controlled and minimized given its potentially catastrophic effects on the end product. Thus, it is vital that specific lead-free alloys of near 10% tin content be consistently selected. Careful recognition and application of these conditions would, therefore, suggest an understanding of the physical properties involved as determined by the compositions of the materials and the thermo-mechanical treatments used. For the assembly under review, dominance of sheet metal items such as those in Fig. 2 indicates that tin, and even copper, was not readily available to most people. The strictness in selecting near 10% tin content, optimal for reducing wall-thickness without sacrificing load-bearing capacity, is also characteristic of an effort to minimize consumption of valued materials. In this respect, the use of considerably more tin in objects #33 and 48 is rather exceptional. The extra cost, however, would have been more than compensated for if the increased tin level enabled similar items to be made with much less material. According to Park et al. (2009), high-tin alloys, through the proper control of thermal treatments and tin levels, can be sufficiently hardened for use in thin-walled functional items. They showed that the best result can be attained when alloys of near peritectic composition (22% Sn) are quenched at around 700 C. In Korea, for example, where access to tin was limited, this particular technology was applied for more than a millennium to
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produce various high-tin objects with walls as thin as a few tenths of a millimeter (Park and Gordon, 2007). By contrast, the tin fraction and heat-treating temperatures inferred from objects #33 and 48 appear to deviate substantially from the optimal conditions mentioned above, thereby suggesting that such technology may not yet have been fully established at that particular megalithic site. Arsenic in copper can lower the liquidus temperature and facilitate casting. In as-cast conditions though, its effect on hardening is virtually insignificant (Lechtman, 1996). In mechanical working, however, arsenic can be just as effective as tin for ensuring product strength and ductility. It is also particularly advantageous in the fabrication of thin plates. The best historical example of this effect being explored can be found in pre-industrial Andean South America where arsenical copper was widely used in the production of sheet metal objects (Burger and Gordon, 1998; Lechtman, 1996). It should be noted that although the bronze assemblage in Fig. 2 consists mostly of sheet metal products, this study found no evidence of arsenic addition being applied for this particular purpose. The paucity of arsenical copper was also noted in the two Indus sites at Lothal and Rangpur in Western India (Kenoyer and Miller, 1999). By contrast, arsenic was frequently used in other Indus sites such as Mohenjo-daro and Harappa in Pakistan. The use of lead in bronze has the effect of lowering melting temperatures and improving flow characteristics, two key properties required in casting operations. It is also beneficial in reducing the amount of costly materials needed such as tin and copper. Yet, despite these advantages, this study found no added lead in the three bells that were cast (objects #6, 26 and 49). Instead, the craftsman, perhaps taking into account the added geometrical complexity of the design, raised the tin level only for object #26, which was cast as a single piece as opposed to the others consisting of two pieces cast separately before being assembled. In a tinlacking environment, the use of expensive tin where cheap lead could have been used just as effectively suggests that copper and related alloys were likely recycled. This would coincide with similar practices widely used in India from the Indus period (Kenoyer and Miller, 1999: 115). Since lead is not tolerated in sheet metal products, lead-contaminated objects cannot be recycled for use in such applications. Thus, extreme care must be taken to prevent further contamination during recycling when mixing lead-based and leadfree scraps. Unfortunately, doing so would have been nearly impossible to achieve in practice. Subsequently, the complete absence of lead intended in any of the specimens examined suggests that a rule or guideline was put in place by these craftsmen to avoid undesirable lead corruption. This rule would likely have not been respected without strict cooperation from among the megalithic communities involved who shared a common exchange network for bronze based products and technology. Since lead was widely used in Indus sites, both as a separate metal and as an alloying element in bronze (Kenoyer and Miller, 1999: 119), it is unlikely that the absence of lead in the bronze objects under review was associated with the availability of raw materials. Table 1 lists nine bangles (#1, 9, 10, 23e25, and 44e46) with a tin content averaging 8.7%. Their load-bearing capacity would not have been a critical factor in determining which materials to use, and even non-alloyed copper would have been strong enough for their intended purpose as an ornament. In fact, of the five bangles from the Indus site at Lothal as reported by Kenoyer and Miller (1999), three were made with copper bearing no deliberate alloying. With regards to the presence of tin in all of the bangles we examined, as with the other functional items, this was likely not meant for strength. Instead, the addition of tin may have been intended to improve color characteristics. If color, therefore, was the only or primary criterion that mattered, improved strength from tin alloying may have allowed a substantial amount of lead to
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be added without any noticeable color change. Doing so would then have allowed expensive tin and copper to be saved. Such lead addition, however, would have prevented these objects from being recycled as sheet metal products for the duration of their use. It should be noted that if bronze ornaments such as bangles remain lead-free, they can readily be forged into practical items. However, without tin addition, they cannot be used until their tin level is raised. This treatment involves melting the product, which presents technological complications and substantial material loss. Another fact to be noted of the bangles in Table 1 is that they were all given a thorough thermo-mechanical treatment after casting. Their microstructures were well annealed and nearly free of any defects such as cavity porosities and brittle d particles. This additional treatment is not required if they are to be used as an ornament. It is necessary, however, if they are to be used as a feedstock for further processing by forging. It is evident, therefore, that the bangles were not produced exclusively for ornamental purposes and, given their well-controlled chemical compositions and microstructures, represent items also used for trade. Such intermediary products could have been forged into other useful items at a later date, thereby meeting a wider range of consumer needs. Moreover, their production and circulation, as a great innovation tailored to suit the unique needs of the megalithic bronze industry, would have given rise to greater freedom and flexibility for both producers and consumers alike. The idea of circulating such pre-alloyed intermediaries ready to be forged into finished items would be even more practical if the raw materials, copper and tin, were not available nearby. Little is known of their sources for the megalithic sites under consideration. According to the data collected by Kenoyer and Miller (1999: 117e118), however, copper smelting slags dated to the early second millennium BC were reported in Rajasthan while Afghanistan was suggested as a likely tin source for Indus sites. The largest tin deposits in the subcontinent were reported in Bihar, but their exploitation began quite recently (Penhallurick, 1986:21). 5. Conclusion Bronze objects recovered from five megalithic sites in the Vidarbha region of India were examined for their alloy compositions and microstructures. The assembly consisted primarily of sheet metal products along with some bangles and small bells. The analytical results showed that the technology involved can be characterized by an extreme dependence on forging during fabrication and a consistent selection of CueSn alloys of near 10% tin. This technological status represents a fully developed bronze tradition optimized and dedicated to the production of thin-walled objects such as those under investigation. In sheet metal technology, lead contamination is detrimental to the material properties of a given bronze object and should, therefore, be avoided if recycling is intended. In the specimens examined, no lead addition was detected. This indicates that a ban on adding lead may have not only been in place but also well respected by the megalithic members of this particular bronze tradition. In addition, the absence of lead in even non-sheet metal products such as bangles and bells, where it would have been highly desirable, suggests that recycling was also an important factor in material selection and product composition. This hypothesis is further supported by the presence of a high tin content which would not have been necessary for the items in their current form, but would have been highly advantageous if the products were to be used as intermediaries and later forged into other functional items. It is not clear how this particular megalithic bronze technology evolved or how it relates to the Indus tradition. One possibility is that, after the decline of the Indus Civilization, it was carried
forward by the indigenous survivors until the onset of the local Iron Age. The key features found in most Indus bronze objects, namely limited tin and negligible lead, suggest that the alloys were primarily made for use in forging rather than casting. These nonoptimized (tin-deficient) alloys likely reflect a restriction in material resources as opposed to a lack of technological sophistication. In this respect, the megalithic and Indus traditions are not so much different as to deny a plausible connection. In the megalithic communities, such a unique bronze tradition dedicated to sheet metal technology may have been a practical choice to take advantage of the changing role of bronze as dictated by the introduction of iron. In sheet metal products, the selection of specific CueSn alloys, with near 10% tin and without lead, is critical to ensuring that strict material properties be maintained. For this reason, the use of more tin was an optimal way to minimize material costs while protecting product integrity. Also, the dominance of thinwalled bronze items, indicative of a resource-limited environment, suggests that both tin and copper were regarded as expensive commodities. As the excavation report for the site at Raipur (Deglurkar and Lad, 1992) showed, the bronze objects recovered mostly came from burials of apparently high-status people. Iron artifacts, by contrast, were given no such distinction. Thus, for the megalithic communities of the Vidarbha region, bronze may have in fact become a more prestigious material, one readily available only for elites who could afford it. This would suggest that a more rigid socio-economic stratification appeared following the introduction of iron technology. As previously mentioned, the megalithic bronze tradition under consideration is uniquely defined by a consistent selection of specific alloys, a perfect control of lead contamination, and an innovative use of ornamental items as multi-purpose intermediaries. These characteristics reflect a high level of standardized technological achievement and testify to the collaborative efforts of the participating communities. Allchin and Allchin (1982: 335), from their typological study on megalithic iron artifacts, proposed that a group of traveling metalworkers disseminated similar technologies across the megalithic landscape of South India, from Nagpur in the north to Adichanallur in the south. The high level of standardization and collaboration, evident in the bronze objects examined, suggests that this theory may be true at least within the Vidarbha region. Continuation of this study is, therefore, recommended to determine if this theory can apply to other megalithic sites in the area and beyond.
Acknowledgments Our work would not have been possible without the kind support from Dr. James Lankton. Thanks are also due to the people of Deccan College who showed hospitality to one of the authors (JSP) when he visited Pune with his wife to take samples for examination. Dr. Jamkhedkar is acknowledged for his encouragement of this work. This project was financially supported by the Korea National Research Foundation (NRF-2012-0029808).
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Penhallurick, R.D., 1986. Tin in Antiquity-its Mining and Trade Throughout the Ancient World with Particular Reference to Cornwall. The Institute of Metals, London. Possehl, G.L., Gullapalli, P., 1999. The early Iron Age in South Asia. In: Pigott, V. (Ed.), The Archaeometallurgy of the Asian Old World, MASCA Research Papers in Science and Archaeology, vol. 16. University Museum Monograph 89, Philadelphia, pp. 153e175. Srinivasan, S., July 1998. The use of tin and bronze in prehistoric southern Indian metallurgy. JOM, 44e50. Thakuria, T., 2010. The Society and Economy During Early Iron Age and Early Historic Period in Deccan with Special Reference to Beads (1000 BC to 500 AD) (Ph. D thesis). The Deccan College Post-graduate and Research Institute, Pune, India.