Cu Metallurgy in Medieval Period

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SUPERIOR COPPER METALLURGY OF EASTERN INDIA AND BANGLADESH IN

MEDIEVAL PERIOD: FROM PURE COPPER TO HIGHTIN BRONZES

Prasanta K. Datta*

Pranab K. Chattopadhyay*

Introduction

The history of East India and Bangladesh has been pushed back to Paleolithic, Chalcolithic and subsequent early

historic times by the findings of archaeological excavations at Paharpur[1], Bangarh[2], Pandu Rajar Dhibi[3], Mangalkot[4],

Mahasthan[5], Wari-Bateswar[6] and elsewhere around Singhbhum copper belt. Other than the mass of copper-bearing

materials collected from the explored sites, very often a large number of copper tools, in caches, so called copper

hoards have been obtained at places nearby. Whatever be the source, fortunately metals preserve their history ofprocessing, of their chemical extraction and physical transformation, in their microstructures. Therefore, a study of

their microstructures can predict their production processes, if assisted with suitable archaeological evidences of

mines, slag, crucibles or molds. Characterisation of four copper samples taken from different sites in chronological

order starting with in and around Christian era from 1st millennium B.C. to 1st millennium A.D. to reconstruct the

remarkable development of copper metallurgy, in Eastern India and Bangladesh.

2.0 Description of samples

2.1 Fragment of a bar-celt, Khuntitoli, (Ranchi), Manbhum Copper hoard

The fragment (Fig.1) is the cutting end of the bar-celt [7]used in scooping the earth of agricultural field, locally

known as khurpi. This is a pure copper casting (99%) but full of gas holes and seems to be made in open molds

with poor gating. The purity (over 99%) is an excellent example of pure copper, though melting and castingtechniques deserve more improvement for good casting production.

2.2 A double-ended axe, Khuntitoli, (Ranchi), Manbhum Copper hoard

The axe (Fig.2) has in plan, convex lead edge; slightly concave side edges which converge towards the rounded

butt[8],[9]. It weighs around 600 gms and has length around 160 mm and thickness 5 mm at the midriff. Made of pure

copper (over 99%) the metal was probably deoxidized with arsenic before pouring in a closed mold. The beautifully

cast piece was then probably hot-forged in super plastic temperature to develop sharp edges, while residual cast

structure were allowed to remain in central section.

2.3 A broken disc of a copper lump, Aguibani, Medinipur

A part of the copper disc (Fig.3) solidified at the bottom of a crucible in form of a half-round is the end product of

an extraction heat. Though shrinkage is not missing and weighs only around 200 gms. it exhibits the size (diameter)

of the crucible in use. The purity (over 99.5% Cu) and the softness achieved in annealed condition suggest a deep

knowledge of metallurgy.

2.4 A broken part of a bronze bowl, Gazole, (Rangmahal), Malda

The broken fragment of a high-tin bronze bowl (Fig. 4) is an example of copper alloying and copper alloy forging.

The half-mm thick section of the bowl demonstrates a high degree of metallurgical skill in complex shaping of a
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difficult hard phase alloy by open-die forging. The corrosion resistance and superior hardness of tin bronze might be

a common knowledge that enhanced its wide use in historical period.

3.0 Microstructure of samples

3.1 Optical Microscopy

The results are shown in Fig.5 to Fig.8. In the sample of the bar-celt (Fig. 5), the remnants of dendrites are visible,with wide distribution of micro-voids and inclusions as well as diffusive layers of dendrite arms revealing unsound

knowledge either in foundry or in heat treatment.

The sample (Fig. 6), of axe shows the break down of coarse dendritic structure in form of equi-axed grains, free

from gas holes with segregation of inclusions and second phase particles mostly in grain boundaries. This indicates

not only superior techniques of foundry like degassing, closed molds, gating etc. but also the development of good

working and heat treatment practice using recrystallization-recovery-grain growth mechanism for producing sound

metals. The sound material has become softer (HK 60-61) than that of the bar-celt, as indicated by the micro-

hardness (HK 70-71) readings.

The copper lump (Fig. 7), which is an ingot, contains mostly equiaxed grains with globular Cu-Cu2O eutectics or

deoxidation products and low-melting constituents of insoluble lead widely distributed. The shrinkage void indicatessound metal revealing deoxidation techniques (here by arsenic) and good annealing treatment of hard arsenical

copper(HK 183 - 185). The bronze sample (Fig. 8), reveals the preferred orientation of hard second phase alpha-

delta in the forging direction in the matrix of -phase (HK 276 - 283). It also vindicates the capability of those

people to hot forge a high tin (over 20%) bronze in a narrow forging temperature range a remarkable feat indeed

in those poor conditions in medieval period. Considering Europeans were not conversant in hot forging of high tin

bronzes even as late as sixteenth century as recorded by Vannoccio Bringucchio in Pirotechnica (1540) of Papal

Foundry in Rome.[10]This was a great achievement by East Indian metal workers. Good strength of the material

proves the soundness as well as excellent manual forging practice .

3.2 Scanning Electron Microscopy

Under scanning electron microscope, the bar-celt confirms the wide presence of inclusions of oxides (Fig. 9) andsulphides and micro-shrinkages. Most of the trace elements are Ni, Co, Sn and Bi, which are present in Singhbhum

chalcopyrites,[11]thereby confirming the natural sources of copper ore and its extraction.

The structure of the axe is the proof of sound metal, which contains arsenides (Fig.10) along with usual oxides and

sulphides, as residual deoxidation products. The central portion, after etching, reveals cast structures (Fig 10, RHS),

which still retains the dendrites of pure copper undisturbed. The unetched copper lump shows (Fig 11, RHS) the

irregular shrinkage cavities. The wide presence of white arsenides (Fig. 11) confirms the intentional addition of

arsenic to refine and deoxidise the metal at the ingot stage. EDAX result (Fig. 11, centre) also proves the presence of

lead arsenides and copper sulphides, generally present in Singhbhum ores The etched structure also indicates ingot

pattern due to slow cooling (~1 K/Sec) obtained from the dendritic arm spacing, calculated of ~100 m, as is

expected in a shut-down crucible.

In case of the bronze sample the interconnected - phase (Fig. 12) look more roundish in nature, indicating veryclose under annealing below transformation temperature like process annealing in carbon steel.

The SEM study establishes the argument that the production process of pure copper from nearby chalcopyrites was

continuously refined over hundreds of years to a useful technology unmatched in the ancient world. The eastern
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people could also develop the technology of copper alloying and forming of high tin bronze, not easily available else

where in India or abroad.

4.0 X Ray Diffraction (XRD), Differential Thermal Analysis (DTA) and Thermo gravimetric Analysis

(TGA) Results.

Table I and II provide X ray diffraction patterns produced by samples. Bar celt, Axe and Lump showbasically - Cu phase as predominate phase with minor phases, almost non-existent. Bronze sample indicate the

presence of /or metastable - phase, along with - Cu phase. Some peaks remain to be identified. For Axe, a

prominent endo peak at (812oC) and a small endow peak (482oC) were observed in DTA. Similarly for copper

lump small endo peaks around (351oC) and (682oC) were observed. All these DTA & TGA results of copper

samples suggest the presence of some amount of low melting constituents, probably of tin, zinc, lead, arsenic and

others in these systems.

5.0 Reconstruction of copper technology Logistics of Production

Copper mines (Hazaribagh, Baragunda, Mosabani and Rakha of Jharkhand) [12],[13], quality wood charcoal (Sal =

shorea robusta wood), fired crucibles, slag heaps, tuyers, alloying metals like Tin, (Ranchi, Hazaribagh, Bastar)[14],

[15] or imports from Thailand or Malay, copper products copper hoards, copper plaques[16], Pala- Kurkihar- Jhewari

Bronzes[17] and lastly copper related names Tamajuri (Heaps of copper), Tamralipta (Pasted with copper), Kansabati

(Carrier of Bronze), Shilabati (Carrier of Stone-Copper Ore), Aguibani (Forest of Fire agun), Mosabani (Forest of

crucibles musa), provide ample evidences for the development of copper metallurgy over two millennia in East

India.

5.2 Extraction Process

Dry balls (large pellets) of powdered copper (sulphide) ores and wood charcoal, bonded with cow-dung and clay as

flux, were stacked in a cylindrical crucible, fitted with a slag notch (in form of a terracotta pipe) at the bottom and a

blast pipe at the top to blow air. The charged crucible was placed in a underground hole and the mass was ignited at

the top with occasional air blast.

The ignition temperature of chalcopyrite is only 300

0

C

[18]

. Iron suphide (FeS) got roasted to iron oxide (FeO) andfluxed with silica were melted out as viscous (viscosity 500 1000 cP) liquid fayalite (sp. gr. 3 3.7) while

remaining FeS Cu2S mixture forming fluid (viscosity 10 cP), heavy matte (sp. gr. 4.4) at the high temperature

percolated to the bottom (Fig. 12). During trickling, on further air blowing FeS again got smelted to FeO and

produced fayalite separating it from Cu-phase, due to the excess silica present in the system. The collected white

metal rich in copper ( 80%) (sp. gr. 5.2), afterward, due to air blowing converted itself to blister copper. The

process resembles the copper extraction process of present Nepal[19], (Gajurel and Baidya,1984), and also the

Continuous Process Technology of advanced countries like Noranda, Mitsubishi, or Ausmeltprocess.[20]In Figure 13

reconstructed furnace is shown and Figure 14 includes Thermodynamic reactors as practiced in most modern

continuous melt process, which closely resembles, the ancient crucible copper extraction of East Indian metal

workers.

The sample of bar-celt is a forged form of blister copper a copper with enough dissolved, residual oxygen whichexpose itself in from of blisters over the copper surface. Later on this type of copper was deoxidized with arsenic-

bearing ore, llingite/ orpiment, so that the material of axe is less gassy. Afterwards the intentional degassing was

made by small amount of arsenic which volatilizes after deoxidizing but some of it remains as residual arsenides

that are found in the structure of the copper lump, from Aguibani.

5.3 Basic chemistry of the Process
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Copper pyrometallurgical extraction process is a stepwise selective oxidation (while iron extraction is a reduction

process) of copper iron sulphide ores (chalcopyrite) by i) roasting ii) smelting iii) converting operations. During

these reactions (SO2) sulphur di-oxide, (FeO) iron oxide (removed as a slag after fluxing) and finally metallic (Cu)

copper are produced with some heat generated. Modern processes combine the three steps together sequentially in a

single continuous process[21], which is, autogeneous in character and made the extraction convenient and energy

economic.Surprisingly, East Indian copper workers attempted the same and successfully extracted pure copper very cheap

probably first time in the world, without any help of modern chemistry (thermodynamics).

(i) Roasting:

2 FeS + 3O2 = 2 FeO + 2 SO2 + Heat

(Gangue, iron sulphide) (from air) (Iron oxide) (Sulphur dioxide)

Roasting conducted with air at temperatures between 5000 and 7000C, mostly removes Fe & S, increasing

concentration of Cu in the product with generation of some heat to facilitate the next reaction.

(ii) Smelting:

The process combines simultaneous generation of liquid metal phase (in form of metallic sulphide mixtures) knownas matte and liquid slag phase (in form of fayalite) for the removal of the gangue, iron. The product rich in copper is

matte (35~50% Cu and balance iron sulphide). Therefore, two separate identities develop - one of which is the

product matte and the other is the discard fayalite slag.

5.4 Thermodynamics of the process:

From thermodynamic point of view, the process hinges on three basic points:

(i) During initial roasting, just sufficient oxygen should be supplied to the reactor (here in crucible) so as to oxidize

iron sulphide to iron oxide for removal of the gangue (here FeS) at moderate temperature and to oxidize carbon and

hydrocarbons to carbon mono-oxide or di-oxide for generation of heat, but inadequate for magnetite (Heavy, sp. gr.

5.0-5.5) formation or sulphate production. Burning of hydro-carbons (cow-dung) raises the localized temperature

(~12500C) quickly, but also arrest magnetite (Fe3O4) generation due to the less oxidizing atmosphere with overalllow temperature (500-5000C), as otherwise there is a chance of moving down of heavy gangue component as

magnetite (sp. gr 5.0-5.5), ahead of (sulphide) matte (sp. gr. 4.4) which can settle below to contaminate final blister

copper (sp. gr. 7.8).

In comparison, in Near East, Mesopotamian metal workers of Sinai region might have used high temperature by

generating huge heat [the presence of superb quality charcoal from wild pistachio, haloxylon amodendronhad been

reported by Agarwal,[22] to accelerate the process, which favoured magnetite formation[23].

(ii) Excess supply of silica separates gangue component (iron) in form of immiscible light liquid slag phase from

fluid heavy metal phase of copper at the smelting temperature (12000C). The application of alumina (in clay) and

lime, this further stabilise the isolation of slag from metal phase in two separate zones (like oil-water separation).[24]

The (~50% Cu, sp. gr. 4.6) matte is heavier with very low viscosity, ~10 cP, so is naturally fluid, while thesmelting slag (sp. gr. 3-3.7) is lighter but viscous (500-2000 cP), (so is rather slow to move) having complete

separate identity, floats over liquid metal phase. The presence of silica causes then to separate into two immiscible

liquid phases an invention of eastern copper workers without the knowledge of modern chemistry. The amount of

silica (SiO2) as a flux is also significant. According to FeO Fe2O3 SiO2 phase diagram (1200o C), the amount

should be at least 40-42% - which may be higher due to the presence of lime CaO [25]. A slag analysis from

Parihati[26] copper producing center confirms this: 65.1% SiO2, 10.3% Al2O3, 9.2% Fe2O3, 0.4% TiO2, 2.5% MgO,

9.5% CaO, 0.07% MnO. This is unique as in Near East (Mesopotamia or Sumer), men used iron ore[27]as flux,
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thereby forming magnetite, which ultimately produced iron contaminated hard copper, difficult to forge or work and

the slag analyses show silica around 40% and not in excess. Comparatively, men in Bengal could completely isolate

iron from copper due to the presence of excess silica, and produced soft, almost pure, malleable copper (HV 60 or

less) - easy to forge, and so having high demand in the world market.

(iii) On progress of smelting, after deslagging through the slag notchthe Cu-rich matte (~80% Cu) known as the

white metal is collected below, and is converted to blister copper by oxidation avoiding contamination. The presence of blow holes (Fig.1) is the probable proof of this premise as blow holes are caused

by the entrapped gases during casting. This is also unique, as in Near East, no slag notch was used in the crucible

and deslagging was absent; the total slag and metal prills was allowed to solidify in the hole[28] and the metal was

separated from the brittle slag by stone hammering. Differences between Near East and East India copper

technologies are given Table III.

5.5 Copper Forming Technology

Floor molding[29] using existing stone pattern of bar celt might had been used in East India to cast the bar-celt by

direct pouring in an open mold. It gave a fast cooling rate of ~ 70 K/Sec as calculated from DAS, ~ 17 m from

micro structure. A better foundry practice was adopted for the casting of the axe, where top mold box could havecovered the flat floor mold with horizontal gating and vertical sprue as is the case commonly practiced by Andhra

tribal casters even to day[30]. The given cooling rate ~ 15 K/Sec, was corresponding to DAS of 30-40 m, justify the

probability. Sandy clay was the probable molding system. Forging was done to give proper shape to the axe after

casting. But it could not develop the desired hardness, (Fig.6) commonly needed for cutting tools. Yet the important

thing is that people knew the hot forging characteristics of copper - as copper is super plastic only above 500-

550 0C.[31]Cold forging could have made the axe harder but brittle, unsuitable for normal use.

The copper lump was the bun-shaped ingot obtained by allowing the pure liquid copper to cool at the bottom of the

crucible. The ingot was probably around 120 mm in diameter with maximum thickness in the central region as 12-

mm. slow cooling within the crucible is vindicated by the large secondary dendritic arm spacing

of 100 m. From the shape of the ingot it seems the crucible had a half-round inside cavity at the bottom and theinternal configuration tapered to 150 mm in diameter towards the bottom.

The open-die forging of high tin bronze presumably was done on a concave grooved stone anvil[32](Mukherjee,

1978), using heavy stone hammers in the super plastic temperature zone [33] (Rollason, 1975) around 600 - 7000C

within a uniform solid solution region. Starting with a flat ingot and finishing with a good forging texture after deep

sinking is a remarkable achievement in ancient time. This is particularly important as only with more than 22% Sn-

Cu alloy has good forging properties above 5000C due to an unique single phase region over eutectoid

reaction[34] which was not thermodynamically known from the phase diagram (Fig. 15) at that ancient time.

6.0 Conclusions

Optical microscopy and SEM observations confirm the development of chemical metallurgy for the extraction of

pure copper from chalcopyrites. Also the gradual progress of physical metallurgy from unsound blister copper

stage or ingot structure to the fine texture of wrought bronzes continued by the people of East India in medieval

period. The application of crucible shaped furnace with slag notch at the bottom while air-blast at the top, fluxing

with silica, deoxidation with first arsenic or tin and later on zinc in historical period are quite unique and

characteristically different from medieval copper technologies available in other parts of the world. Each of these

establishes the notion about the indigenous origin of copper technology in East India although some assimilation of

outside knowledge cannot be discounted.
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Acknowledgements

The authors express their sincere thanks for Ms. Mira Roy, Man in India, Ranchi and Dr. Gautam Sengupta,

Member Secretary, CASTEI, Kolkata for the provision of samples for testing. Shanaj Husne Jahan has helped a lot

for publishing this esteemed Journal.

Abbreviations

Sp.Gr. Specific gravity.

cP Centi Poise, unit of viscosity.

DAS Secondary Dendritic Arm Spacing, = 101.R 0.42(R Cooling Rate, K/Sec)

m Micro-meter (10-6 m). ( in m.) (Hwang, et. al, 1998)[35]

HV Micro hardness in Vickers Diamond scale.

HK Micro hardness in Knoop Diamond scale.
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Table I

XRD Results

Sample: Bar-Celt- Axe, Cu lump Radiation: Cu / Fe 35 kV / 30 mAWavelength, K = 1.791

N0. Angle(2 ) d, I / Io1 50.8o 2.088 1002 59.2o 1.813 413 88.6o 1.282 30

The result show predominant - Cu phase on the basic of main peaks, with some minor Cu phases (Ref:JCPDS, 1978).[36]

Table II

XRD Results

Sample: Gazole Bronze (23.62% Sn- Cu) Radiation: CU / NI 35 kV / 30 mA

Wavelength, K = 1.540598 N0. Angle(2 ) d, I / Io

1 22.895 3.8813 84.22 30.050 2.9714 70.83 32.606 2.7441 70.44 39.219 2.2952 82.25 41.726 2.1629 71.46 42.337 2.1332 69.37 44.459 2.0344 100.08 49.117 1.8534 32.19 52.750 1.7340 30.6

10 58.353 1.5801 31.811 71.066 1.3254 28.012 78.132 1.2223 23.013 85.863 1.1309 29.014 87.325 1.1157 24.715 109.850 0.9412 17.8

XRD result indicate the presence of " (peak no. 4,5,7,8,11,12,13), - metastable (1,3,4,6) and - Cu

phase (7,9,12) of Copper Tin system. (compared with JCPDS, 1978, 06 0621, 17 0865).[37]
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Table III

Tabulation of Differences

Near East Process East Indian Process

Ores

Rich Chalcopyrite ores probably

were used in small granules:(a) Less Silica in ore.(b) Less surface area was exposed in

chemical reaction.

Lean ore Fine powders of

Chalcopyrite were used:(a) More silica - making it almost self fluxing.(b) More specific surface area -giving option of quick liberation ofsulphide ores for chemical reaction.

EnergyMore heat is required for oreliberation energy requirement washigh.

Less heat is required for chemicalreaction. Therefore, it was energyefficient.

Flux

Iron ore was used as flux, therebycontaminating sulphide ore with the

production of miscible slag andmetal phase.

Silica was used as flux in form ofclay/cow dung mixture makingimmiscible fayalite slag whichseparates it self from metal phase.

Slag notch

Removal of gangue, was not possible, for non availability ofnotches so the product was ironcontaminated copper.

Gangue, in form of light liquid slagwas removed from metal phasethrough bottom notch, making metalmore cleaner.

DeoxidationIron contaminated copper cannot beeasily deoxidized.

Deoxidation by arsenic ore or laterTin or Zinc was possible.

BronzePreparation

Tin Bronze (10 - 22% tin) is notmalleable for hot forging. Castingwas done only.

High tin bronze (over 22% tin) has asingle phase region, which hasgood forging properties.


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Figure 1. BarCelt. Figure 2. Double-ended Axe

Figure 3. Disc of a Copper Lump Figure 4. Part of a Bronze Bowl

BAR CELT

Figure 5. (LHS) Partially annealed dendritic pattern resembling cast structure (125 X). Microhardness markings are on the righthand structure (Load 10 gm) which indicate higher hardness than the hardness of the blister copper.

AXE

Figure 6. (LHS) Preferential segregation of the second phase particles at the grain boundaries can be seen with usual micro-hardness readings on the right hand side structure (Load 10 gm) which are similar to copper.


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COPPER LUMP

Figure 7. (LHS) Equiaxed grain structure with random distribution of second phase is observed. (Inset) Some lead (Pb) particles.

Microhardness readings show harder material (Load 50 gm), confirming the presence of arsenic bearing second phase

BRONZE BOWL

Figure 8. (LHS) Banding of second phase - , in Bronze indicates hot forged structure, matrix is phase.Microhardness

readings indicate the presence of , - phase (HK 323, Load 10 gm).


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Co 0.33 Cu 69.89 Cu 100.00 O 46.18 S 24.38 All in AtomicNi 0.36 S 30.11 S 10.71 Cu 62.18 Percentage

Cu 48.12 Base Metal Co 0.42 Se 8.73

Sn 0.79 Sulphide inclusion Ni .58 Pb 4.71O 50.40 (Irregular, black) Cu 24.30 (Irregular, gray)

Oxide inclusion As 1.78 Selenium Copper Sulphide(Round, gray) Bi 15.02

(White) Complex sulphide, oxide, arsenide

Figure 9 Figure 10 Figure 11

Figure 9. Unetched microstructure is full of different inclusions as indicated above. Bulk phase is copper, along with different metals intrace amounts even Pb, Bi, Co, Se and Arsenides are rare.

Figure 10. Microstructure of axe is the proof of sound metal, with arsenides along with usual oxides and sulphides.Figure 11. Microstructure showing cast structures pure undisturbed copper showing the irregular shrinkage cavity.


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- matrixFigure 12: Discontinuous phases in the matrix indicate interrupted manual forging operation (500X); second phase also indicates fibrous

texture. SEM confirms the observation of wrought structure (50X). phase is the matrix while is the second phase rounded due toslow cooling. Small amount of phase can be seen in the central region as well as at the grain boundary.

Figure 13: Reconstructed furnace as practiced by Nepalese copper worker, reported by Gajurel and Baidya, and found in archaeologicalexcavations at Nalanda or elsewhere in India, reported by Prof. A.K. Biswas et al. Dr. H.C. Bharadwaj etc. where silica (SiO2)was used as a flux to drive out iron oxide in form of immiscible liquid slag through the bottom slag notch and produced purecopper free from iron. (LHS).

Figure 14: (RHS) Thermodynamic reactors as practiced in most modern continuous melt process, which closely resembles, the ancientcrucible copper extraction of East Indian metal workers.


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Figure 15

Figure 15: A part of Cu-Sn phase diagram. The part shows the relevant bronze compositions as used in bronze forging. The single-

phase region, below the peritectic temperature of 7980 C, extends from 22% to 25.5% tin.

* Professor, Department of Metallurgy and Material Science, Jadavpur University, Kolkata, India.

* Senior Fellow, Centre for Archaeological Studies and Training, Eastern India, Kolkata, India.

[1] K.N. Diksit,Excavations at Paharpur Bengal, Memoirs of Archaeological Survey of India, No. 55, 1938, Delhi.

[2] K.G. Goswami,Excavations at Bangarh (1938-41), Asutosh Museum Memoir, No. 1, 1948, Calcutta: University of Calcutta, India

[3] P.C. Dasgupta, P. (1964). The Excavations at Pandu Rajar Dhibi Bull. Directorate of Archaeology, West Bengal, No.2,

1964, Calcutta

[4] A. Ray and S.K. Mukherjee, Excavation at Mangalkot, Pratnasamiksha, Vol. 1, 1992, pp. 107-125

[5] M.S. Alam and J.F. Salles (2001) First Interim Report (1993-1999) France- Bangladesh joint venture excavations at

Mahasthangarh, Dhaka: Department of Archaeology, 2001.

[6] K.K. Basa and S.S.M. Rahaman Bronze knobbed bowls from Wari, Bangladesh: Implications for trade,Journal of Bengal Art,Vol. 3, 1998, pp. 291-98.

[7] J.C. Brown Copper Hoards from Ranchi,Journal of Bihar and Orissa Research Society, Vol. 1, 1915, pp.125-26.

[8] S.C. Roy, A find of ancient bronze artifacts in Ranchi district, Journal ofBihar and Orissa Research Society, Vol. 2: 1916, pp.

482-83.

[9] P. Yule and M. Thiel-Horstmann, The prehistoric metal objects in the S.C. Roy collection, Ranchi,Man in India, Vol. 65,. No. 2:

1985, pp. 121-138.

[10] E.G. West, Copper and its alloys Ellis Horwood Series- 1982, p 107.

[11] D.K. Mitra, Seminar onCopper Metallurgy in India, Met. Engg., Jadavpur University, Calcutta, 1984, pp. 18-19.

[12] A.K. Biswas,Minerals and Metals in Ancient India, New Delhi: D.K. Printworld, 1996, pp. 187-88.

[13] H.C. Bhardwaj, List of Ancient Mines,Aspects of Ancient Indian Technology, Delhi: Motilal Banarsidas, 1979, pp. 191-193.

[14] M. Mukherjee,Metal Development in India,Met. Engg., Jadavpur University, 1978, pp. 3-6.

[15] B.B. Lal, Further copper hoards from the Gangetic basin and a review of the problem, Ancient India, No.7, 1951 pp. 20-39

[16] D.C. Sircar, Aspects of Early Indian Economic Life, Sec.-III, Bulletin Indian Museum V-XIV, No.1 & 2,1979, pp. 26-29.

[17] R. Chatterjee, Important Hoards and Finds in East Indian Bronzes, Ed. S.K. Mitra, Calcutta University, 1979, pp. 125-32. A.K.

Bhattacharya,Jhewari Bronze Buddhas, Calcutta: Indian Museum, 1989.

[18] W.G. Davenport and A.K. Biswas, Extractive Metallurgy of Copper, 1978, p. 69.

[19] C.L. Gajurel, K.K. Baidya, Copper Extraction Process Traditional Arts and Crafts of Nepal, Delhi: S. Chand), 1984, p. 12.[20] R. Matusewicz and J. Sofra,Non-ferrous Metals in the New Millennium, Ed. R. Bhima Rao, K. Sarveswara Rao, V.N. Misra (Allied

Pub.), 2001, pp. 71-94.

[21] W.G. Davenport and A.K. Biswas, op. cit. p.86(iii) Converting:

(a) Complete FeS - elimination or slag forming stage from matte

2FeS + 3O2 + SiO2 2FeO .SiO2 + 2SO2(Iron sulphide) (From air) (Silica, flux) (Fayalite slag)The liquid Copper Sulphide (Cu ~80%) remains in the reactor known as white metal.(b) Blister (Pure) Copper Forming Stage:

Cu2S + O2 2Cu + SO2 + Heat(White metal) (from air) (Blister Copper)
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It is to be noted that copper forming (2 nd stage) does not occur until the matte contains less than 1% Fe (iron).[22] D.P. Agarwal, The Copper Bronze Age in India, Munsiram Manoharlal, New Delhi. 1971, p. 110.

[23] W.G. Davenport and A.K. Biswas, op. cit. p. 14

[24] W.G. Davenport and A.K. Biswas, op. cit. pp. 91, 96.

[25] W.G. Davenport and A.K. Biswas, op. cit. p. 88.

[26] M. L. Datta, Spectrographic Determination of Minor Constituents in Ancient Copper Slag Trans. Indian Instituteof Metals, V-85,

No.5, 1982, pp. 487-88.

[27] B. Rothenberg,Excavations at Timna Site 39 a Chalcolithic Copper smelting site and Furnace and its Metallurgy Report on

Timna Site 39A IAMS Monograph, No.1, Archaeo-Metallurgy, 1978, pp. 21

[28] B. Rothenberg, (1978) op. cit. p. 21

[29] M. Mukherjee, Metal craftsmen of India, Calcutta: Anthropological Survey of India, 1978, pp. 204-210.

[30] M. Mukherjee, op. cit., 1978, pp. 210-230.

[31] C.J. Smithells (1978). Metal Reference Book, London: Butterworthh Heinmen.

[32] Mukherjee, op. cit. 1978, pp. 210-213.

[33] E.C. Rollason,Metallurgy for Engineers (ELBS), 1975, pp. 300-318.

[34] E.G. West (1982), op. cit. p 185.

[35] P.D. Hwang, et.al.Journal Material Engineering and Performance, Vol. 7(4), 1998, pp. 495 503.

[36] JCPDS, Selected Powdered Diffraction Data for Metals and Alloys, 1978, Ed.

[37] JCPDS, Selected Powdered Diffraction Data for Metals and Alloys, 1978, Ed.
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