Metallurgy and Archaeology: A case study on iron objects from the

megalithic sites in Nagpur, India

Jang-Sik Parka • Vasant Shindeb

1. Introduction
Bronze and iron objects are among the most important archaeological materials bearing
crucial information on the role of an ancient region or community in the creation and
transmission of cultural ideas and practices. The production of bronze and iron involves a
series of engineering processes including the smelting of raw materials from ores, and the
making of alloys and various thermo-mechanical treatments applied in fabrication. Each of
these individual processes can be achieved in a number of different ways depending on
technological and sociopolitical environments. These processes can be combined to establish
a unique technological tradition that reflects temporal and regional characteristics. The
individual engineering processes and their combination in space and time can only be traced
through the application of strictly scientific methodologies developed in metallurgy. This fact
emphasizes the importance of metallurgy in archaeological investigations to the general
understanding of ancient communities.
The early iron technology based on bloomery smelting was presumably invented in the
West and diffused toward the East while another technology based on cast iron originated
from the East and made its way to the West (Maddin 1996; Needham 1980; Rostoker and
Bronson 1980; Tylecote 1992; Wagner 1996). The data currently available on bronze
technology also demonstrate the existence of spatiotemporal variations in alloy making as
well as in fabrication techniques (Barnard 1961; Chernykh and Kuzminykh 1989; Park et al.
2011). In spite of the importance of bronze and iron artifacts as a potential means for
exploring the history of ancient India, not much is known of the regional technological status
relating to their production, let alone the role of India in the creation and diffusion of the
related technologies. With this problem in mind, this article will focus on some Indian iron
objects and illustrate the nature of data attainable from metallurgical investigations and their
interpretation.
It is interesting to note that some of the most important iron objects from the megalithic
sites at the Nagpur district in Maharashtra, India were made in unique shapes reminiscent of
those excavated in the southern part of the Korean peninsula. Despite the substantial distance
in geography and chronology, the similarity in their typology leads one to suspect the
particular iron objects as suggestive of an ancient interaction between the two regions that has
yet to be discovered.
The Korean counterpart includes a special family of iron artifacts in the form of narrow
plates with a fan-shaped blade on one or both ends. Those with a blade only on one end,
basically axes, have generally been recovered from earlier sites than those with blades on
both ends. It is generally accepted that the latter evolved from the former with certain
modifications in shape, and eventually replaced the former. These plate-type objects have
continuously been recovered from sites of the first century BC (Yi et al. 1989) and onwards,
primarily in the former Gaya and Silla territories located near the southern coastal area of the
Korean peninsula. Given their frequency, abundance and the substantial variation in their
shape and size, they must have represented the iron industry of the two kingdoms. They were
made of low carbon iron, frequently with slag inclusions spread in ferrite backgrounds. Some
of them were given a carburization treatment on both ends. This would allow them to meet a
wide range of consumer needs at the time as effective intermediaries yet to be shaped into
edged or pointed objects, with minimal forging and thermal treatments. This plate-type object
could best be produced directly from bloom iron though it could also be made indirectly from
treating cast iron.
A collaborative research project has been launched to find evidence, if any, for the
possible exchange of specific technological ideas that may have been responsible for the
appearance of typologically similar artifacts in India and Korea. As an initial step to this end,
some of the iron objects excavated from the megalithic sites at Nagpur, which are currently
stored in the Deccan College, were examined for their microstructures and chemical
compositions. During the selection of objects to be examined, it was immediately evident that
the sites had also produced numerous copper-based objects. Evidently, the bronze metallurgy
must have played a crucial role in the megalithic communities and provides another topic of
significance to be probed in the future for the understanding of their cultures.
A number of iron and bronze objects from the Indian megalithic sites are currently under
careful examination using metallurgical techniques to characterize the associated
technologies in terms of smelting, alloy making and various thermo-mechanical treatments
done in fabrication. Some of the preliminary results thus far obtained from the iron objects
will be presented in this article, with a special emphasis placed on identifying specific
technologies practiced at the sites, which will then be compared and contrasted with those
practiced in ancient Korea.

2. Experiments
Small metallographic specimens taken from the selected iron objects were mounted and
polished following standard metallographic procedures. The specimens were then etched with
a solution of 2 volume % nitric acid in methanol for the examination of their microstructures
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 and reported in weight fraction.

3. Results
Figure 1a and 1b present the general appearance of two axes recovered from the
megalithic burial sites at Khairwada and Mahurjhari, respectively, in the Maharashtra
province of India. Arrows a, b and c shown in both axes locate the respective spots at the
blade, flak and rear from which specimens were taken for metallographic examination. Figure
1c-1h are optical micrographs illustrating various structures at different parts. The
micrographs are placed in the column below the axe they represent and Figure 1c, 1e and 1g
and Figure 1d, 1f and 1h present the structures at the blade, flank and rear of the associated
artifact, respectively. The dark rhombuses in the micrographs are the result of the Vickers
Hardness measurements made using a 500 g load. The hardness of each specimen is specified
by the numbers given near the rhombuses. The substantial difference observed in hardness is
associated with the varying microstructures determined by the carbon levels of the specimens
and the thermal treatments applied in fabrication. In both axes, the specimens from the flank,
represented by Figure 1e and 1f, consist of relatively soft ferrite grains whose carbon content
is negligible. The blade and rear, however, contain microstructures that are much harder than
ferrite and attainable only in high carbon steels. It is to be noted that Figure 2c-2h all contain
non-metallic inclusions spread over the metal background.
Figure 2a-2d present SEM micrographs providing a highly magnified view of the high
carbon structures shown in Figure 1c, 1d, 1g and 1e, respectively. Figure 2a and 2b are
similar in that they consist primarily of pearlite structures containing 0.77% carbon. The
structure in Figure 2a from the blade, however, contains tiny particles of cementite spread
over the pearlite background whose inter-lamellar spacing is much finer than that in Figure
2b from the rear. By contrast, the high carbon structures shown in Figure 2c and 2d from the
other axe contain evidence of special thermal treatments that were applied during fabrication.
The structure in Figure 2c from the blade is morphologically similar to the martensite phase
that forms upon quenching. However, the Vickers hardness value Hv=438, as determined by
the size of the rhombuses in Figure 1d, is substantially lower than those normally obtained in
fresh martensite of a comparable carbon level. This lower hardness implies that the specimen
was tempered following a quenching treatment in an effort to reduce brittleness at the
expense of hardness. Figure 2d from the rear consists of the cementite phase precipitated in
the form of networks against the ferrite background. This peculiar structure, which does not
develop in the normal eutectoid phase transformation, demonstrates that the specimen was
given an excessive tempering treatment subsequent to quenching. As a result, the hardness
measured in Figure 1h (Hv=258-296) is much lower than that in Figure 1d.
Figure 3a and 3b present iron objects recovered from the megalithic site at Khairwada.
They are in the form of a thin plate that is much longer than it is wide. They are of uneven
width, which increases to either end giving the impression of a blade. The point of minimum
width is positioned near one end that is much smaller than the other. This shape does not
suggest any specific functional purposes. They were recovered from the majority of the
megalithic sites excavated in Nagpur, frequently in larger quantities than any other items, and
may have played an important role in the local iron industry. Figure 3c-3h, optical
micrographs, are arranged in a similar manner to those in Figure 2. Figure 3c, 3e and 3g and
Figure 3d, 3f and 3h illustrate the microstructures at the front blade, flank and rear blade of
the object in Figure 3a and 3b, respectively. The micrographs from the object in Figure 3a all
consist of ferrite grains with some non-metallic inclusions elongated along the forging planes,
indicating that the artifact was forged out of almost pure iron. However, the specimens from
the other artifact are shown in Figure 3d, 3f and 3h to have been made of high carbon steel
whose carbon level is near eutectoid, i.e., 0.77%. The specimen from the blade of this object
is severely corroded and intact structures are found only at the narrow band running
diagonally from the upper left corner of Figure 3b. The structure in this band consists mostly
of pearlite with a little ferrite precipitated at the grain boundaries, suggesting that the original
structure was more or less similar to that in Figure 3f. The absence of ferrite in Figure 3h
implies that the carbon concentration in this specimen is a little higher than the others. Non-
metallic inclusions are also found present in this object, particularly in Figure 3f.

4. Discussion
In both functional and technological aspects, axes such as those shown in Figure 1a and
1b constitute a typical member of the group including various edged and pointed objects and
may best represent the general iron tradition established in an ancient community. The
microstructure data of the axes examined show that the specimens from their flank consist
mostly of ferrite while those from their blade and rear end are filled with the phases observed
in high carbon steel. The dominance of the ferrite phase in their flank suggests that the axes
were made primarily of low carbon iron. The increased carbon level in the other specimens
suggests a special treatment that was intended for functional purposes. Though it is not clear
at the moment how the carbon level was adjusted, it was likely achieved either by the
carburization treatment directed at the specific parts or by joining a steel strip where required.
In any case, the technology involved in their manufacture can be divided into two stages
including the production of the raw material, which is low carbon iron, and the control of
carbon concentrations, termed steelmaking in modern terminology. Specifically in India
where there was no large-scale production of cast iron until quite recently, low carbon iron
readily available in the megalithic communities must have been the product of bloomery
smelting. Then the best technique for steelmaking, i.e., raising the carbon level is
carburization in which pieces of iron are heated for a prolonged period inside a burning
charcoal environment to induce carbon penetration from the surface. The iron tradition in the
megalithic sites under consideration may therefore be characterized by the use of a bloomery
process in smelting and carburization in steelmaking. The level of technological
sophistication achieved by the local ironworkers is clearly evident in one of the axes where
quenching followed by tempering was applied. This cannot be done without the complete
understanding of the material properties as determined by the complicated phase
transformations that are induced through the fine adjustment of treating time and temperature.
In bloomery smelting, forging has to be applied near the end of the process for the
removal of slag inclusions, and the final product naturally takes on the form of a plate.
Therefore, if no restriction is imposed on the carbon contents, plate-type objects similar to
those in Figure 3a and 3b can readily be manufactured directly out of the smelting process
itself. The presence of elongated non-metallic inclusions in most specimens from the two
objects is a clear indication of the forging given for the dual purpose, i.e., the removal of slag
and the shaping of the objects. In view of the carbon levels that are generally very low in
bloomery iron, the high carbon structures observed consistently in all the specimens from one
of the plates indicate that it was subsequently treated in a steelmaking process based on
carburization. The unique shape and size of the present objects were probably determined by
taking into account the conditions imposed in manufacture and use such as the furnace
configurations in carburization, treating time and temperatures, and the ease with which they
were handled in fabrication, transportation and actual service. For instance, if an iron plate is
to be carburized in a furnace set at 1,000C within a working day to the same extent as found
in the object examined, its thickness should be on the order of 1 mm.
Although no specific usage is suggested in their appearance, the plate objects examined
hold in their unique shape and microstructure crucial information on the infrastructure of the
local iron industry. It is certain that both were initially forged out of low carbon bloomery
iron. Their peculiar shape suggests that they were not a final product but served as
intermediaries for an engineering process yet to be performed. One of them consisting of high
carbon phases indicates that they were used as a feedstock in a carburization treatment. No
iron tradition can be established without an effective means for steelmaking. In this respect,
the plate-type objects examined must have played a crucial role in the successful
establishment of the Indian megalithic iron tradition by serving as a component of the
particular steelmaking process through carburization. In theory carburization can be applied
to objects of any shape and size. In practice, however, it could be a complicated and costly
procedure without the proper facilities and technical skills. In general, steel is needed only at
a critical part such as edges and points, as is exemplified in the two axes in Figure 1a and 1b.
There are two choices that can be made when an increased carbon level is required only on a
limited part of an object. In one case, carburization treatment is directed at the specific part
after the object has been finished shaping. In another case, small pieces of steel are first
prepared and then attached to the main body at the critical location. The iron plates shown in
Figure 3a and 3b correspond evidently to the latter case. One such plate can be used in
making a number of edged or pointed objects such as axes, chisels, adzes, awls, nails and
arrowheads if properly cut horizontally, vertically or both. As such, the production and
circulation of these plates in the Indian megalithic communities must have given much
freedom to the ironworkers. It is expected that they allowed the suppliers to specialize in
fewer items while the consumers enjoyed the freedom to meet their varying needs with a
minimum work and technological requirements.
In his recent paper, Park showed that the ancient iron industry of Korea, particularly in
the southern part of the peninsula, was established based on the production and circulation of
special plate-type iron objects. In earlier times, they were made in the form of axes just like
those shown in Figure 1a and 1b. With the passage of time, their shape changed to that of a
thin rectangular plate with a fan-shaped blade attached on either end. These objects are
remarkably similar to those presented in Figure 3a and 3b in their role as versatile
intermediaries that can be used to make a variety of edged and pointed functional objects and
thereby meet a wide range of consumer needs. In addition, they were both forged out of low
carbon iron and their fanned-ends were often carburized. Despite the differences found in
their exact shape and the extent of carburization, it is difficult to deny the possibility that they
were somehow related. The recent evidence presented for the practice of bloomery smelting
in the southern part of the Korean peninsula (Park and Rehren 2011) suggests that the Korean
objects, like their Indian counterparts, were also produced directly from low carbon bloomery
iron rather than from the indirect and complicated process involving cast iron. By contrast,
plate-type iron artifacts so far reported in China (pers. comm. Dr. Chen at the School of
Archaeology and Museology of Peking University) are distinctly different in appearance and,
more importantly, were all made indirectly from cast iron. The existence of the unique plate-
type iron objects in ancient Korea, therefore, challenges the premise that the Iron Age in
Korea began and developed with the dominance of the Chinese style of technology, based on
cast iron, and raises a serious question on its origin. A future study is necessary to determine
if the iron tradition of the Indian megalithic communities had any influence on the beginning
of the iron production in ancient Korea.

5. Closing Remarks
The analytical data presented above show that the use of a bloomery process in smelting
and carburization in steelmaking constitute two major factors characterizing the iron tradition
of the Indian megalithic communities. It is likely that the plate-type objects examined played
a key role in the successful establishment of this tradition in the megalithic iron industry.
They could be used as intermediaries to be forged into critical parts of various tools and
weapons and also as a means for trade. In the latter case, their value would depend on size
and carbon levels. The invention of such intermediaries reflects the high level of
technological status that was achieved by the megalithic ironworkers in an effort to maximize
the potential of the specific iron tradition under the given social and cultural environment.
The existence of such an advanced technology naturally raises a question on its origin,
development and diffusion in space and time. Typological examination of the iron objects
from a group of the megalithic sites within the district of Nagpur suggests that they shared a
common iron tradition. It is yet to be discovered, however, if this is the case with other
megalithic sites scattered over the vast territory of the Indian subcontinent. It would be of
great interest to see if the technological sophistication as apparent in the objects examined
came to exist as a result of the innovations made during the megalithic period or if it was
inherited from the previous native civilizations or was driven by foreign influences. The
evolution of this particular iron tradition in the subsequent generations provides another topic
of significance to study.
It is interesting to note that some plate-type iron objects showing remarkable similarities
in typology and technology appeared first in the Indian megalithic communities and then in
the southern coastal area of the Korean peninsula. Despite the substantial difference in space
and time between the two regions, the technology applied in their production as well as their
role in iron industry seems almost identical. It is even more interesting to realize that similar
objects have not been reported in China, which has long been considered as the sole origin of
Korean iron. This is not surprising, however, since the specific objects can best be produced
directly from bloomery iron rather than indirectly from the Chinese style of technology, based
on cast iron. The evidence recently identified for the practice of bloomery smelting in South
Korea supports that these iron plates were likely produced directly from bloomery iron. This
theory is supported by their Indian counterparts that were indeed an outcome of the bloomery
tradition.
Our collaborative research is just beginning and many more iron and bronze objects from
collections with varying chronological and regional contexts must be subjected to a rigorous
scientific examination to reach a more general conclusion. Nevertheless, the results presented
above reveal important information that can hardly be obtained without the integration of
metallurgy and archaeology. More importantly, this information stimulates numerous well-
defined questions of substantial significance to be generated, which may readily be solved in
the future research to the better understanding of the history of India and Korea and their
probable interaction in the past.

Acknowledgements
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 extreme
hospitality to one of the authors (JSP) when he visited Pune with his wife to take samples for
examination. This project was financially supported by the Korea National Research
Foundation (NRF-2011-0029808).

References
Barnard, N., 1961. Bronze Casting and Bronze Alloys in Ancient China. Monumenta
Serica Monograph 14, The Australian National University and Monumenta Serica, Canberra.
Chernykh, E.N., Kuzminykh S.V., 1989. Ancient Metallurgy in the Northern Eurasia
(Seyma-Turbino Phenomenon). Academy of Sciences of the USSR Institute of Archaeology,
Moscow <NAUKA> (in Russian).
Maddin, R., 1996. The history of the evolution and development of metal. Proc Forum
for Int Conf on the Beginning of the Use of Metals and Alloys (BUMA-IV). Shimane, Japan
January 16-17.
Needham, J., 1980. The evolution of iron and steel technology in east and southeast Asia.
In: Wertime T.A., Muhly J.D., editors. The coming of the age of iron. New Haven: Yale
University Press; pp. 507-41.
Park, J.S. 2011. A preliminary study on the role and implication of plate-type iron
artifacts in the ancient iron technology of Korea. Journal of Archaeological Science,
forthcoming.
Park, J.S., Honeychurch, W., Chunag, A., 2011. Ancient bronze technology and nomadic
communities of the Middle Gobi Desert, Mongolia. Journal of Archaeological Science 38,
805-817.
Park, J.S., Rehren, Th., 2011. Large-scale 2nd to 3rd century AD bloomery iron smelting in
Korea. Journal of Archaeological Science 38, 1180-1190.
Rostoker, W., Bronson B. 1980. Pre-Industrial Iron Its Technology and Ethnology.
Philadelphia: Archaeomaterials Monograph No.1.
Tylecote, R.F., 1962. Metallurgy in Archaeology – A prehistory of Metallurgy in the
British Isles. Edward Arnold, London.
Wagner, D.B., 1996. Iron and steel in ancient China. E.J. Brill, Leiden·New York·Köln.
 Wagner, D.B., 2008. Science and civilization in China Joseph Needham Volume 5
Chemistry and chemical technology Part 11: Ferrous metallurgy. Cambridge University Press.
Yi, K.M., Yi, Y.H., Yoon, K.J., Shin, D.G., 1989. Research report of excavation of the
Proto-Three-Kingdoms burial site at Tahori in Uichang-gun. Kogohakchi (Jornal of the
Institute of Korean Archaeology and Art) 1, 5-174 (in Korean).