History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t4: (IV) Iron and Steel

History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t4

Language: English

(IV) Iron and Steel

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The discovery of iron and its technological development on the Indian subcontinent has raised many questions because of the lack of archaeological proof dating back to those existing at Lustrian in Iran and other centres of ancient civilization. There is a total absence of iron objects at the Harappa and Mohenjodaro sites but the recent excavations at Lothal,Ahar(1300 B.C),Gufkral (1300 B.C.),Atranjikhera (1025 B.C.),Tadkanhalli(1000 + 150 B.C.) Hallur (1000 to 900 B.C.) and Khairadih (1000 + 100 B.C.) have pushed back the beginning of the iron age to the same period as those outside India. *Fig. 9* shows the 14C dating of the iron objects found at some of the important excavation sites of India and its shows a definite trend of simultaneous development and appearance of this metal all over India. *Table 2* gives the chronology of development of iron tools and other objects during the early, middle and later stages of the development of iron age in the country. This table clearly shows a gradual widely spread development of the use of iron which is possible only under the conditions where the knowledge of the use of these artifacts is lacking. This indicates that in all probability the iron technology in India is independent of the copper technology and it might have been developed even before copper.

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This hypothesis is further supported by the nature of the deposit of the mineral of the two metals, and comparatively easy method of obtaining iron from the oxide

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Fig. 9. 14C dating of some of the iron objects found at different archaeological sites in Indian subcontinent Table 2 — Various tools and implements appearing at the three stages of iron technology growth

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| Tool Type | Name of Tool | Early Stage | Middle Stage | Late Stage |
| **Hunting Tools** | | | | |
| | Spear heads | * | * | * |
| | Arrow heads | * | * | * |
| | Points | * | # | # |
| | Socketed tangs | * | # | # |
| | Blades | * | * | # |
| | Spear lances | # | * | # |
| | Dagger | # | * | * |
| | Sword | # | * | * |
| | Elephant goad | @ | * | * |
| | Lances | @ | @ | * |
| | Armour | @ | @ | * |
| | Helmet | @ | @ | * |
| | Horse bits | @ | @ | * |
| | Caltrop | @ | @ | * |
| **Agricultural Tools** | | | | |
| | Axes | * | * | * |
| | Sickles | * | * | * |
| | Spade | @ | * | # |
| | Ploughshare | @ | * | # |
| | Hoe | @ | * | * |
| | Chisel | @ | * | * |
| | Pick | @ | # | * |
| **Household Objects** | | | | |
| | Knives | * | * | * |
| | Tongs | * | # | # |
| | Discs | @ | * | # |
| | Rings | @ | * | # |
| | Spoons | @ | * | * |
| | Sieve | @ | @ | * |

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| Tool Type | Name of Tool | Early Stage | Middle Stage | Late Stage |
| | Cauldron | @ | @ | * |
| | Bowls | @ | @ | * |
| | Dishes | @ | @ | * |
| Building Materials | | | | |
| | Rods | * | # | # |
| | Pins | * | # | # |
| | Nails | * | * | * |
| | Clamps | * | * | * |
| | Pipes | @ | * | # |
| | Sockets | @ | * | # |
| | Plumb bob | @ | * | # |
| | Chains | @ | * | * |
| | Door hooks | @ | * | # |
| | Door handle | @ | @ | * |
| | Hinges | @ | @ | * |
| | Spikes | @ | @ | * |
| | Tweezers | @ | @ | * |
| | Anvils | @ | @ | * |
| | Hammers | @ | @ | * |
| | Scissors | @ | @ | * |
| | Saw | @ | @ | * |

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* indicates definite existence; @ indicated non-existence;

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indicates that confirmed data is not available.

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ore than copper from the sulphide ores. In India while iron ore Fe2O3 and Fe3O4 are occurring as surface deposits embedded in the Quartz and Dolomite minerals below the gound level. This aspect of the discovery and development of iron technology has been discussed in detail by Prakash, B. (1990) and from this view point the earlier attempts of correlating the discovery of iron to P.G.W. and N.B.P. in the Northern India seems to be inaccurate, although iron implements appear along with these potteries at many sites.

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The survey of ancient literature has provided ample proof that iron and steel making technology and their difference has been known in the Vedic period (vide reference on Rgveda and Yajurveda) and may be even earlier. These evidences also support the hypothesis of Sharma R.S. that Aryans were the original inhabitants of India and this also supports the use of iron both by Aryans and Dravidians even in the pre-historic period. As cited earlier Indians of the Vedic period were using steam powered transport vehicles and they were capable of producing many types of war weapons and agricultural tools which is possible only by the use of iron and steel. Prakash and Tripathi(1986), and Kulkarni(1989)have published a detailed review on this metal and listed chemical composition of many of the iron objects. These objects have carbon content of 0.03 to 1.3% and they are basically Fe-C alloys. The *Suśruta Saṃhitā* has mentioned the method of fabrication (700 B.C.) of more than 100 surgical tools made of Fe-C alloys and the process of heat treatment to obtain razor sharp edge capable of splitting hair into two halves longitudinally.

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*Fig. 10* gives the sketch of some of these tools prepared on the basis of their description in the text. *Fig. 11* shows the collection of iron swords and daggers etc. collected from the excavations at Tinnevelley dating back to 400 + 100 B.C., and *Fig. 12* and 13 show various iron objects found at Atranjikhera dating back to 1200-1000 B.C.

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Some of the massive iron objects manufactured in India in the Christian era have no parallel in the world, such as the famous Iron Pillar at Delhi (4th century A.D.) weighing 6000 kg, Iron Pillar at Dhar (12th century A.D.), weighing 7000 kg, 29 iron beams at Konark in Orissa (9th century A.D.), of which the longest one measures 11000 mm in length and 175 by 197 mm in cross section weighing about 3000 kg, the iron trident at the temple of Achaleshwar on mount Abu, the iron pillar at Kondachari and the iron trident at the temple of Tanginath near Bishunpur in Bihar. Some of these are shown in *Fig. Nos. 14 to 18*. The massivity of these objects and their high corrosion resistance have kept the modern metallurgists and technologists wondering about the manufacturing and processing details as well as the cause of their such high corrosion resistance.

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*Fig. 10. Sketch shows some of the surgical tools designed by Suśruta* (IV.1) Iron Minerals and Smelting Technology

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Fig. 11. This photograph shows some of the Iron swords and daggers found at Tinnevelley (400 B.C.)

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Iron occurs in nature mostly as Fe₂O₃(Hematite) and Fe₃O₄ (Magnetite) and some Pyrite deposits (FeS) have also been known. Besides this, in some parts of the world Meteoric Iron has also been found and used for the early war weapons. Iron of Meteoric origin is easily distinguished by its high Nickel content.

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India has been bestowed with one of the largest and richest deposits of Hematite, Magnetite and their hydrated forms like limonite etc. and these deposits are spread all over India. These deposits have been worked all over India to produce sponge iron or wrought iron using variety of furnaces and archaeological remains of a number of furnaces have been found at Nalanda, Naikund, Khairadih, Ujjain and many other sites. Fig. 19 shows a sketch of the reconstructed furnace dating back to 700 B.C. As can be seen this furnace has been constructed from prefabricated refractory clay blocks or bricks, whereas the furnaces used in Western Asia and Europe in the same period were either made by digging a hole in the earth or by arranging stone pieces to give the desired shape. These furnaces were generally used only once and then discarded after taking out the hot bloom. That is the [Figure: Iron Weapons : Period III: 1-8, Arrow heads; Spearhead; 10. shaft 1/2 Fig. 12. Some of the iron objects excavated at Atranjikhera (~1000 + 200 B.C.)]

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[Figure: Iron Tools and Implements: Period III: 1-3, clamps; 4-6, chisels; 7-8 , Bars; 9-10, Borers; 11, Needle 1/2 Fig. 13. Some of the iron tools and objects found at Atranjikhera (~1000 + 200 B.C.)]

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probable reason for the occurrence of a cluster of furnace remains at the sites excavated in the West, whereas in India the furnaces seem to be reused after relining and repair with refractory clay. Buchanan (1807), Hadfield (1912) and Verier (1942) have given detailed description of the working of a large variety of iron smelting furnaces and the steel industry prevailing in the country during 17th to 19th century. Ray (1956), Joshi (1970), Banerjee (1965), Krishnan (1955), Prakash B. (1983) Chatterjee and Altekar (1973), Bhardwaj (1982) and many others have surveyed the available information and published excellent reviews and books on the subjects.

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Fig. 14. Iron Pillar at Delhi and its microstructure at the bottom of the pillar

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The smelting of iron in the past was done only by a special group (caste) of persons in each tribe and they all worshipped the God ‘Asura’. This may be because in the early days of the discovery of this metal it was being used only to make war weapons and hunting tools (refer *Table 2*), and the general public being peace-loving the handling of this metal was considered the work of ‘Asura’ who gave devilish power in the hands of man. The belief of the ancient iron smelters in lord ‘Asura’ has been so strong that his image was put even in the ‘Mandala’ of ancient iron making in Japan (Buddhist period) as can be seen from *Fig. 20* which shows the painting of ‘Kāla Bhairava’ and ‘Asura’ working for the iron smiths (Prakash, B. 1990). In Bihar, Orissa and Eastern part of Karnataka the iron smelting was carried out, by these ‘Asuras’ and in Central India by ‘Āgārias’. Verier (1942) and Joshi (1970) have written in great detail about the ‘Āgāria’ tribe and their iron smelting practice spread through the central province, Rewa, Udaipur, Sirguja, Ranchi and Koraput etc. *Fig. 21* shows the region of India in which according to Verier (1942) Āgārias were smelting iron. In some places they are confused with ‘Lohārs’ or ‘Lohārins’(blacksmiths) but as Verier (1942) has described, while Āgārias smelted the iron ore to produce wrought iron blooms ‘Lohars’ shaped the rough iron to manufacture various tools and objects and carried out suitable heat treatment operations. In the year 1982 Prakash and Igaki (1984) surveyed the district of Bastar where iron making by Mundia tribe was mentioned and they could locate one furnace in the interior of the jungles of ‘Bastar; at Loharpara as reported in their paper.

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Fig. 15. Dhar Iron Pillar broken into three pieces. The change from square to octagonal section at the top can be seen

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At Bishunpur on the road between Lohadāga and Netārhat (near the Bihar, Madhya Pradesh border) Sharma, M. has located the site where iron smelting was being done earlier, and his group has got it revived under a rural development plan ‘Vikas Bharati’. There the smelting is done by Birjias and Lohars both belonging to the Asur tribe. A detailed report on this revived iron smelting has been published by Prasad, K.K. (1990) and his group. For recent survey, vide Sahasratudheya et al (1993) of P.P.S.T. Foundation.

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IRON TEMPLE SAMPLE MICROSTRUCTURES

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[Figure: AVERAGE COMPOSITION C .27 S .05 O18 Cr NIL Co .09 Mn TRACE .04 Si .50 Ni NIL W .16 P .006 O15 Cu NIL Ti NIL Al .040 HARDNESS 80 B 115 VPN IRON BEAMS]

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*Fig. 16. Iron beams (12 century A.D.) lying at the Sun temple of Konark*

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The ancient iron making practice consisted of the following operations and each one of them was performed under the strict supervision of the oldman or master craftsman of the tribe. The operation of the furnace was considered to be a sacred ritual and they prayed to the tribal God ‘Asur’ for the success of the smelting. Many of the ‘Mantras’ and verses have been preserved as folk songs and these have been vividly described by Joshi (1970). The secret of iron smelting process was very religiously guarded and passed on only to the younger generation of the family or tribe. Women had active role to play in the process and certain specific jobs were to be done only by them. In *Rasa Ratna Samuccaya* a full chapter has been devoted to describe the characteristic features of the female helper ‘Kalini’ and her duties during such religious rituals.

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The whole operation of the furnace can be divided into five parts

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i. Collection and preparation of the raw-material

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ii. Making of the furnace and its dressing

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iii. Making of air bellows and their fitting

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iv. Ignition of the furnace and its operation

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v. Handling of the sponge iron.

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Following is a short account of the furnace operation :

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Fig. 17. Iron Pillar at Kondacheri

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(i) Collection and preparation of the raw-material: Iron ore - mostly weathered soft Heamatite ore was used but in some regions like in Assam and South India magnetite sand has also been used for the extraction of iron. The operation was generally carried out in the vicinity of the ore deposit or in the nearby forest where suitable charcoal could be made from the wood. It was the duty of the experienced men to locate suitable deposit of the ore and dig it out after performing the puja. Women used the help in transporting the ore and breaking it into pea size (3-5mm). In Mandla before starting for the collection of the ore a ‘mantra’ was recited for the success.

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The translation of this ‘mantra’ is as follows:

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“Go and seek Lohār Mātā, God lead on bed, trusting thee I follow”

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Evidences have been found of mining even at a depth of more than 10m.

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Charcoal – Charcoal was prepared from wood like Irool (Xylia dolaberiformis) Teak, Babul (Acacia arbica), Sal (Shorea rubusta), Bamboo (Caleotropis gigantica) etc. yielding dense and heavy charcoal. It was prepared by cutting the dried branches and trees and burning them into an open heap or inside a pit and when the wood was charred the fire was extinguished by covering the burning wood with green leaves and twigs, and sprinkling water on it. After the fire has completely died out the charcoal was collected and used for smelting. In the latter period Beehive type of firing chambers were introduced for controlled charring of the wood.

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Fig. 18. Iron Trident (Trishul) at Tanginath temple near Netarhat (M.P.)

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Flux – No evidence of the use of lime stone or lime as flux has been found except the SiO2 and CaO present in the ore and the charcoal ash. Some times SiO2 has been added to the charge to make the fluid 2FeO-SiO2 slag. Ayurvedic charges for ‘Satvapatan’ i.e. extraction of metals from minerals have used Borax as flux. The first use of lime as flux in iron smelting has been found at Ujjain (M.P.) and Bairut (Rajasthan), where this technology went through a faster growth.

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(ii) The iron making furnaces and its dressing: Variety of small and large furnaces have been described by Joshi (1970), Banerjee (1965), Krishnan(1955), Prakash(1983), Chatterjee et al. (1973) and Ghosh (1964) and many others, which have been in operation during the 17th and the 18th century in various parts of the country. These furnaces were called Bhaṭṭi, Kothi or Koṣṭhi and they were made from locally available clay, and at many places internally lined with natural china clay or a refractory mixture generally used for crucible manufacture. More details [Figure: CIRCULAR CLAY BRICKS BLOOM CHARCOAL TUYERE TAPPED SLAG CINDER Fig. 19. Iron smelting furnace found at Naikund (700 B.C.)]

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about this mixture will be given later. These furnaces were either made below the ground level or on the sloping face of a hillock or above the ground level.

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They can be classified into three main groups :

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(a) the furnaces of South India having bowl shaped hearth and conical shaft. The furnace was made generally below ground level. Fig. 22 shows a picture of a furnace from Salem which has been made above the ground level.

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From the study of this furnace it seems that a former or inner mould made of read or other thin wood was being used to give the desired contours to the interior of the furnace.

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(b) the second type was cylindrical furnace of Madhya Pradesh, where the bloom was removed from the top,

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(c) Kothi type furnace of Bhopal and Ujjain zone were much larger as compared to the others and had square or rectangular cross- section.

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Figs. 23 to 25 show photographs of different types of furnaces which were in operation during 17th to 19th century. All these furnaces had two holes at the bottom, one for introducing the blast and the other for removing the molten slag. Generally a slanting platform of bamboo, lined with mud, was prepared at the mouth of the furnace to preheat the charge and to push it inside the furnace. A picture of a bowl type furnace which the author studied in 1981 is found at Lohārpārā in the district of Bastar. The line diagram shown in Fig. 26 gives the details of this furnace made in one of the walls of a pit below the ground level. Fig. 27 shows a line diagram of a twin hearth furnace described by Buchanan which was capable of Fig. 20. Reproduction of wall painting from an iron working site in Japan. This painting shows that Japanese craftmen also worshiped ‘Lord Asura’ as in India producing 250 kg of iron per day in the Malabar area. The furnace was fitted with more than one pair of bellows, and peep holes were suitably located to monitor the temperature inside the furnace. Mahamud(1988) has described a furnace from Assam which is asymmetrical in design as shown in Fig.28. One of the walls of this furnace is slanting and this was probably designed to smelt Magnetite sand. Table 3 gives the detailed dimensions of most of these furnaces as available in the literature.

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Diagrammatic Illustration of the Wall Hanging Stature of the Blacksmith God

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Moon

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Sun

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Sanbo-Kojin (A God of mixture of Buddhism and Shintoism)

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God's suite

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God's suite

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Two Devils (employed by Sanbo-Kojin) drive away a woman (symbol of carnal appetite and worldly thoughts)

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Bellows

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Mandarine Orange

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Rice cake

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Wife of Mester

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Master

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Assistan Devil

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仏教金剛力士像奉納日野崎準次郎

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三寶大荒神鍛冶刀匠元祖敬具

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Fig. 21. Map of Central India showing the region in which ‘Āgārias’ were active in the production of iron. Agarias carrying iron ore for smelting

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Fig. 22. Iron smelting furnace from Salem, showing the use of former made of reed to make the inner contour of the furnace

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Fig. 23. Artists impression of the operation of iron smelting furnace using two men to operate a pair of 'Bhathi'

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Fig. 24. Primitive blast furnace of Nagpur region

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Table 4 gives technical analysis of the design features as compared to those of a modern Indian furnace producing more than 1000 tonnes of iron per day. These design features have been calculated on the basis of the design principles of the modern furnaces as discussed by Bashforth(1973).

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A study of Table 4 shows that the ancient furnaces listed in Table 3 were not merely dug out holes or shafts built above the ground level but they were made [Figure: MALABAR IRON FURNACE CAPACITY : 54 kg. TIME - 40 TO 60 HRS SCALE - 1'= 1" (.. .. .. .. 1800)]

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Fig. 25. Photograph of the iron smelting furnace found at Lohārpārā in Bastar

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Fig. 26. Line diagram of the Bastar furnace

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*Fig. 27. Line diagram of the twin shaft furnace from Malabar (as described by Buchanan)*

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based on certain design parameters and principles although they have been of different shapes, sizes and from different parts of the country, and these design principles are very similar to those followed in the design of modern furnaces. For example the throat to bosh diameter (d:D) ratio was 0.28 to 5 in almost all the ancient furnaces while the modern furnace has a value of 0.7 to 0.77. The maximum diameter at the bosh or tuyere level determines the combustion rate of fuel in the furnace and the d:D ratio takes care of the thermal as well as reduction expansion of the ore. The difference between the values of ancient and the modern furnace may be due to the change in the nature of the charge i.e. ore, etc. and the use of coke instead of charcoal in the modern furnace. In a similar manner the stack angle and H/D/2 ratio also shows a good similarity with those for the modern furnace. The useful volume of the furnace has changed from furnace to furnace and for the larger furnace (1000 tonnes) it is 760 m³, but there is a good agreement on the volume of the furnace chamber (cm³) required per kg of iron produced by the direct reduction technique.

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This value decreases to 358 cm³ in the case of the modern furnace because of the indirect reduction promoted in the stack and also higher temperature and productivity attained in this furnace. The decreased size of the mouth of the furnaces indicate that the ancient craftsmen were conscious of the importance of gas-solid contact time and the control of gas velocity inside the furnace. All these design Geometrical Outline of the Furnace.

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Fig 1 D J C F E 9 8 6 A K H B Fig 2 D G F E A C B Fig 3 S S S 7 7 A B C Fig 4 a b 5 7 7 e d Fig 5 Fig 5 Back Fig 5 Front Fig 6 Fig 7 Fig 8 Fig 9

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*Fig. 28. Iron smelting furnace having asymetrical shaft (as described by Mahamud. Figure numbers indicated in this picture refer to various parts and their position in the main furnace*

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features must have been achieved after keen observation and experience of operating large number of furnaces. It is important to note that Indian smelters had achieved these optimised conditions with time inspite of their ignorance of modern physico-chemical principles and the changes occurring in the raw material during reduction.

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Table 3 — Technical details of ancient iron furnaces

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| Sl No. | Location of furnace | Shape | Cross section | | Heigh t cm | No. of bellow | Capa- city kg | Remarks |
| | | | Max cm. | Mouth cm. | bellow | | | | |
| 1. | Madhya Pradesh | Circular | O.D.107 I.D. 43 | O.D.56 I.D. 12 | 137 | two | 16 | Made above ground level |
| 2. | Madhya Pradesh | Rectangular | 122 × 76 | - | 122 | four | 214 | Two furnaces made into a pit of 122 × 305 × 91 cm smelted 380 kg of ore in 3 hrs.made from clay bricks |
| 3. | Nagpur | Square | 56 × 56 | 51 ö 25 | 92 to 122 | two | 5 | - |
| 4. | Rajdoha | Circular | O.D.107 I.D. 46 | O.D. 56 I.D. 13 | 132 | two | 18 | One heat took 6 hrs. and consumed 80 kg of charcoal |
| 5. | Nalanda Valley | Rectangular | 56 × 81 | 51 × 25 | 90 to 122 | two | 5 | Charge consisted of 25 kg ore, 25 kg charcoal |
| 6. | Salem | Circular | 61 | 31 | 90 to 153 | two | - | A chimney was fitted over the mouth as shown in Fig. |
| 7. | Mandla | Circular | O.D. 78 | O.D. 16 | 76 | - | - | - |
| 8. | Chiglabec ha (Koraput) | Circular | I.D. 30 | I.D. 15 | 95 | two | - | Hearth of furnace below ground level |
| 9. | Jiragora (Koraput) | Circular | I.D. 25 | I.D. 7.5 | 57.5 | two | - | Below ground level |
| 10. | Kamarjod a (Joda, Bihar) | Circular | I.D. 30 | I.D. 7.5 | 67.5 | two | - | Above ground level |

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During the year 1990 the author had a chance to witness the construction and operation of the ancient reduction furnace at Bishunpur where ‘Vikās Bhārtī’ was trying to get this process revived as a rural technology. The two old men of ‘Birjia’ tribe who had seen the operation of iron smelting furnace in their younger days were persuaded to make a furnace and try to revive the technology. The remains of a number of furnaces has been found at Bishunpur, and these furnaces are supposed to be working 50 to 100 years before. *Fig.29* shows the line diagram of the furnace constructed at the ‘Vikās Bhārtī Centre’ with the twin bellows (*Bhāthi*) in position. The furnace has 500 mm internal diameter at the bottom and 150 mm at the top and its height is 800 mm. Its 150 mm thick wall was made from a locally available clay and it was allowed to dry for few days. The shrinkage occurring during drying was patched-up by pressing the clay and applying a fresh coating.

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After about a week’s time when the clay wall was still moist the front opening of about 300 mm width and 200 mm height was cut open as shown in the figure. This opening was made for preparing the bottom of the furnace, fixing of the clay tuyere pipe and removing the molten slag. The top diameter was measured by old craftsman using a piece of stick and then the excess clay was scrapped away. The taper and bottom diameter of the furnace was checked by dropping a wet clay ball from the top inner edge and then measuring the distance between the centre of the ball mark and the wall. The process was repeated several times all round the circumference of the top inner edge. After correcting the furnace shape and size the inner wall was coated with a locally available non shrinking refractory clay. The bottom of the furnace was made from a mixture of charcoal powder and the mud clay to have a taper towards the opening. Inside the bottom opening a clay pipe having shape like a trumpet with about 50-60 mm diameter at the larger end and 20-25 mm at the smaller end was fixed as shown in the figure and then the mouth was sealed with the clay-charcoal powder mixture. The bamboo pipe of the two air bellows or foot operated *Bhāthi* were fixed at the mouth of the clay trumpet as shown in *Fig.29*. Finally the furnace was dried by kindling a fire inside it and slowly raising the temperature to bake the furnace. Now the furnace was ready for operation.

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(iii) *Design of the Air Bellow (Bhāthi)*: The air to the furnace was provided by a pair of small bellows made of goat or buffalo skin and connected to the furnace Table 4 — Technical analysis of the design of Ancient and Modern furnace(calculated from the data given in Table-3)

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| Sl.No | Location of the furance | Furnace cross section | d:D ratio | H/D/2 ratio | Stack angle | Furnace Volume (V1) | V2= cm³/kg | Remark |
| | | | | | | V1 = KD²H (m³) | | |
| | | | | | | P | | |
| 1. | Madhya Pradesh | Circular | 0.28 | 6.37 | 81.1 | 0.13 | 7916 | Direct Reduction |
| 2. | Rajdoha | Circular | 0.28 | 5.77 | 80.1 | 0.14 | 7758 | - |
| 3. | Salem | Circular | 0.51 | 3.97 | 75.9 | 0.22 | - | - |
| 4. | Mandla | Circular | 0.21 | 2 | 64 | 0.23 | - | - |
| 5. | Chiglabecha (Koraput) | Circular | 0.5 | 6.3 | 81 | 0.04 | - | - |
| 6. | Jiragora | Circular | 0.3 | 4.6 | 77.8 | 0.02 | 6654 | - |
| 7. | Kamarjoda (Bihar) | Circular | 0.25 | 4.5 | 77.5 | 0.03 | 30150 | - |
| 8. | Bastar | Circular | 0.83 | 6.6 | 81.4 | 0.23 | 5285 | Value of K should be Different |
| 9. | Madhya Pradesh | Rectangular | - | - | - | 0.57 | - | - |
| 10. | Nagpur | Square | 0.4 | 9.76 | 84.1 | 0.16 | 31987 | - |
| 11. | Nalanda Valley | Rectangular | 0.28 | 9.76 | 84.1 | 0.24 | 48535 | - |
| 12. | Modern Indian Blast Furnace | Circular | 0.7 to 0.77 | - | 81.9 | 760 | 358 | Indirect reduction |

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D - Maximum diameter (Bosh)# d - Throat diameter# H - Furnace height# 0° - Stack angle# P - Production kg/heat# K - Constant (0.5) for soft ore# V1 - Useful volume# V2 - Volume cm³/kg iron through the bamboo and clay pipes. The bellow (*Bhāthi*) was either made from green bamboo sapling bent to form a circle of about 300 mm diameter or by taking a block of wood and giving it a shape like a trough having 300 mm inner diameter. In case of the bamboo ring two such rings were covered with the leather to give it a shape like a bellow and in the case of the wooden bellow only the top was covered with the leather. There was a hole in the top cover and a leather flap attached to it acting as one way air inlet valve. The bamboo pipe fitted to one side of this bellow was about 500 mm long and had a 12-15 mm diameter hole. The height of the side wall was about 80-100 mm. *Fig.30* shows a photograph of an old pair of bellows. The leather top of the bellow was kept taught with the help of a leather string tied between it and one edge of a green bamboo sapling fixed in the ground at an angle as shown in the figures. The pair of bellows was operated by a single man standing on them and pressing alternately. The operator used two sticks to support himself as shown in some of the figures. Sometimes in order to increase the force two persons stood on the same bellow. The only improvement made in the latter period to increase the size of the bellow and operate it by hand either by sitting by the side of it or with the help of a lever as shown in some of the figures latter in this text, used for melting of steel and non ferrous metals.

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VIEW OF PERMANENT STRUCTURE (a)

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SECTION A-A WITH TEMPORARY CHARCOAL WALL AND TUYERE IN POSITION (b)

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Bamboo and rope for support

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Slag pit

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Bamboo air pipes

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Fig. 29. Line diagram of the Iron smelting furnace reconstructed and operated at Bishunpur

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No further improvement was done in these bellows as indicated by the technology of China, Japan or Western countries because the ancient Indian smelters of iron had realised the fact that blowing excess air will lead to the production of brittle cast iron and not solid sponge or wrought iron.

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(iv) *Preparation and operation of the furnace*: It was the duty of women to clean the surrounding of the furnace, roast the ore and break it into 3-5 mm sizes, store sufficient quantity of charcoal and also repair the furnace with clay. They also prepared ‘nari’ clay, piled sand, earth and red iron ore dust near the furnace and also stored sufficient quantity of water in wooden *Kotana* (trough) and earthen pots.

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Fig. 30. Photograph of a pair of ancient Bellows made from hide.

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The furnace bottom was prepared as explained earlier and after fixing the clay tuyere and bellows in position and closing the front hole the furnace was lit after performing the puja and charging it with charcoal. The furnace temperature was raised by operating the bellows at slow pace. When the furnace was red hot and CO gas was seen burning at the top. The furnace was charged with pre-heated ore and charcoal in alternate layers. The preheating of the ore was done by storing it on the inclined platform (*mācān*). *Table 5* gives the charging schedule and operating parameters of the Jiragora and Bishunpur and the latter furnace under operation. An oil lamp can be seen put near the furnace to take precaution against CO gas poisoning. The four thermocouples fitted in the furnace to record the inside temperature are also visible in this picture.

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Table 5 — Comparison of operating parameters of Jiragora and Bishunpur iron making furnaces

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| Operation | Time | Material Ore | charged Coal | Blowing Rate | Remark |
| **Jiragora Furnace** | | | | | |
| 1. Furnace Preheating | 1 hr | | 8 kg | Faster than 87 strokes/min. | See Table VI |
| 2. Reduction stage | 4 hrs | | 14 kg | 87 strokes/ min. | Sequence of ore and coal charging not available. |
| 3. Consolidation stage | 1 hr | | 8 kg | Vigorous blowing | |
| 4. Total operating time | 6 hrs | | | | |
| 5. Total material charged and metal produced | - | 24 kg | 30 kg | | 5.6 kg of iron |
| **Bishunpur Furnace** | | | | | |
| 1. Furnace Preheating | 1.25 hrs | 2.5 kg | 3.25 kg | 40-50 strokes/min. | Fce. Temp. 550 ° C |
| 2. Reduction stage | 4 hrs. | 8 kg | 16 kg | 60-70 strokes/min. | -950 ° C |
| 3. Consolidation stage | 0.5 hrs. | 1 kg | 2 kg | 110 strokes/min. | 1500 ° C |
| 4. Total operating time | 5.75 hrs. | - | - | | 2.5 kg of iron |
| 5. Total material charged and metal produced | - | 11.25 kg | 21.5 kg. | | |

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During the operation of the furnace the bellows were worked at controlled pace to maintain the furnace temperature of 1000 to 1100°C.It took about 6 hours to complete one heat on small furnaces. During the last campaign of the heat the rate of air blowing was increased and a maximum temperature of 1500°C was achieved at the tuyere level. At this stage a small hole was made in the front wall to tap out the molten Fayalite slag. During this period the reduced sponge iron got consolidated in the hearth by partial fusion. The out flow of liquid iron-carbon alloy (C 2%) was considered to be a bad omen. After tapping out the final slag the tuyere and bellows were removed and the front wall was broken to take out the hot sponge iron block.

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(v) *Handling of sponge*: The hot iron bloom taken out of the furnace was hammered on stone anvil to squeeze out the liquid slag as much as possible before it is solidified. This porous sponge iron block was repeatedly heated in a forge hearth to reforge and refine the wrought iron thus produced. The refining treatment can be called the secondary treatment.

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*(IV.2) Secondary Treatment of the Hot Sponge*

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After the hot sponge (weighing about 3-9 kg) was consolidated into a semi-porous mass by forging and squeezing out the molten slag (Fe₂ SiO₄) it was further refined to remove the remaining FeO and Fe₂SiO₄ slag and at the same time increase the density of the solid iron block or rod. For this the block was repeatedly heated in a forge hearth and SiO₂ was sprinkled on it so that remaining FeO may get converted into Fe₂SiO₄ or FeO.Fe₂SiO₄ Eutectic (M.P. 1170°C) i.e. fluid slag and flow out of the semisolid mass.

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The iron piece was repeatedly forged to separate maximum possible quantity of the slag and convert the spongy mass into a solid rod of 15 mm dia x 150 mm length. This refined bar was classified into various categories on the basis of its ductility and appearance of the fracture. This standard refined wrought iron bar was sold to blacksmiths (Lohar) or steel makers for further refining and fabrication of various war weapons and agricultural implements etc. An assessment of the metallurgical properties of the iron produced by the Bishunpur craftsmen has already been published by Prasad K.K. et al. (1990)

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*(IV.3) Extraction of Iron from Biotite by Ayurvedic Method*

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In *Rasa Ratna Samuccaya* and other Ayurvedic text a number of processes have been mentioned for the extraction of iron from Biotite and other iron bearing minerals for the preparation of medicine. This process is known as *Satvapātana*, and generally consists of three major steps : (i) *Śodhana* (purification), (ii) *Bhāvana* (Maceration and Trituration),(iii) *Dhamana* (Heating and smelting).

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*Śodhana*(RRS 2/16) is the process of purification involving heating and quenching of the mineral in some vegetable extract or liquid for several times (7 times or more). The liquids used for *sodhana* of biotite are :

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(i) *Kānjī* (Acidic fermentative liquid),

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(ii) *Triphalā* quath (Decoction of a mixture of Terminienelia chebula, Termenelia belerica and Embelica officinalis).

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(iii) Cow’s urine.

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(iv) Cow’s milk.

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This process is accompanied with intermediate Bhāvana and finally pelletization of the treated mineral mixed with certain other ingredients. The pellets are charged into a Muṣa (crucible) and heated to high temperature in Aṅgār Koṣṭhi shown in Fig.31. This sketch of the furnace, capable of attaining 1400°C, has been described in RRS text.

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For the satvapātan of iron from Biotite (RRS2/28) the proportion of the charge materials is as given below.

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Mica (purified) - 200 gms Borax (flux) - 50 gms Musali powder (reductant) - 50 gms

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To this powdered mixture sufficient quantity of water was mixed, pelletised to 25-30 mm balls and dried in the Sun. This process of extraction of iron from Biotite has been studied in detail by Jha et al. (1989) and they have concluded that maximum yield of the metal is obtained only by the charge mixed in the above mentioned proportion.

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(IV.4) Classification of Iron-Carbon Alloy

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The ancient knowledge regarding the classification of iron- carbon alloy was well developed and an idea of this knowledge can be had from slokas 70-71 of Rasa Ratna Samuccaya in the 8th-12th century A.D. In this book the iron -carbon alloy has been classified into three main groups :

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Fig. 31. Line diagram of ‘Aṅgār Koṣṭhi’ as described in RRS

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i) Kāntā Loha (soft iron)

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ii) Tikṣṇa Loha (High carbon steel)

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iii) Muṇḍa Loha (cast iron)

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Based on the characteristic features of the fractured surfaces and other properties such as ductility, magnetism and hardness etc. these have been further classified into sub-groups as shown in Fig.32. This type of classification has no parallel in the world. Samuel(1980) writes that for the first time it was only in 1772 that ‘Reamnur’ distinguished between grey, white and mottled cast iron fractures. From the study of the classification of iron-carbon alloy, it is obvious that in India iron technology was much advanced and the ancient craftsmen were capable of selective use of various grades of this alloy. Fig. 33 shows the solid state of the modern iron-carbon equilibrium phase diagram and the hatched band shows the range of iron-carbon alloys produced by the ancient Indians. It is very clear that these alloys were either soft iron (range X) containing little pearlite in the matrix of ferrite (low C steel 0.1 to 0.4% C), or (range Y) high carbon steel (0.7 to 1.5% C) containing cementite in a matrix of pearlite. In some steels the carbon content was found to be as high as 1.9%. It is also very clear that various categories of the iron-carbon alloy

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Fig. 32. Classification of Iron-Carbon alloys as described in RRS (8-12 century A.D.)

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Temperature

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1600 1500 (δ) 1400 1300 1200 1100 1000 900 α + γ 800 (α) 700 600 500 0 0.4 0.7 1.0 1.5 2.0 3.0 4.0 5.0 6.0 Carbon content %

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Fig. 33. Fe-C Equilibrium diagram showing the X and Y ranges of the Fe-C alloys produced in ancient times

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were judiciously blended and used for different purposes as discussed later in this text.

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*(IV.5) Process Control During Iron Making*

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From the study of the phase diagram it is very obvious that the ancient Indian smelters had gained high level of skill in operating the iron smelting furnaces and they were applying strict process control to produce iron containing 0.1 to 0.4% C and rarely iron containing carbon in the higher range.

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Prakash, B. (1990) has done a detailed study of the operating parameters and heat and mass balance of some of these furnaces and he has observed that the furnace temperature was controlled to 900 to 1000°C during reduction and raised to 1250 to 1300°C in the last phase by controlling the blowing rate of air as shown in Table 5. Bloomgren and Tholander (1986) have studied the constitution of iron smelting slags and the environmental conditions inside the low shaft furnaces and they have concluded that Fayalite (2FeO.SiO₂) slag or its Eutectic with FeO having a melting point of 1205°C and 1170°C respectively prevent the carbon pick up by the reduced iron, and thus in this process the furnace productivity is decreased. *Tables 6* and *7* show the heat and mass balance for the Jiragora furnace operated by the tribals in the presence of Ghosh(1964) and this has confirmed the aforementioned

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Table 6 — Heat balace of ironmaking furnace at Jiragora (M K Ghosh)

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| Sl.No | Heat Input | K Cal | S.No. | Heat output | K Cal |
| 1. | Heat generated by combustion CO/CO₂ = 4 | 81,011.5 | 1 | Heat for heating the ore to 1000°C | 4,920.00 |
| | | | 2. | Heat for endothermic reduction | 5,451.87 |
| | | | 3. | Heat content of metal at 1200°C | 1,385.00 |
| | | | 4. | Heat content of slag at 1200°C | 6,300.00 |
| | | | 5. | Heat in outgoing gases | 48,026.28 |
| | | | 6. | Heat lost by conduction and radiation by difference | 14,928.22 |
| | **Total 81, 011.5** | | | | **81,011.5** |

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% Radiation loss = 18.5%

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Theoretical Flame Temperature = 1,938°C Blowing Rate: Air blown in 6 hrs = 203 m³ Air blowing rate = 564 litres/min No of strokes for blower size (280 mm dia, 100 mm ht) = 87/min Note: Maximum capacity of worker = 300 strokes/min

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Furnace operation practice :

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| Operation | Time | Coal charged | Blowing Rate |
| 1 | Furnace Pre-heating | 1 hr | 8 kg | Faster than 87 strokes/min |
| 2 | Reduction stage | 4 hrs | 14 kg | 87 strokes/min |
| 3 | Consolidation stage | 1 hr | 8 kg | Vigorous blowing |

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Table 7 — Material balance for ironmaking from Jiragora (M K Ghosh). Furnace trial results show 24 kg of ore/30 kg of charcoal. Time of reduction and smelting - 6 hours. Reduction efficiency 36.2%

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| Material | Analysis | Calculation | Metal Fe(kg) | Theoretical Composition | Actual Composition (basis 21 kg) | Gases (kg) | Remarks |
| Ore-24 kg | | | | | | | |
| Fe(Fe2O3) | 63.4 | 24x0.634x0.302 | 5.5 | 9.7 | 9.66 | 2.357 | Metal Composition |
| SiO2 | 2.44 | 24x0.0244-0.021 | 0.01 | 0.565 | 5.68 | 1.387 | C-0.4% |
| P2O5 | 0.01 | - | 0.0004 | - | - | 0.114 | Si-0.2% |
| Al2O3 | 1.66 | - | - | 0.446 | 1.41 | 0.026 | Fe-rest |
| CaO+MgO | 0.5 | - | - | 0.12 | 1.29 | - | Slag |
| MnO | 0.9 | - | - | 0.20 | 0.21 | 0.888 | Composition |
| Lol | 3.7 | - | - | - | - | - | SiO2-27.08% |
| | | | | | | | Al2O3-6.72% |
| Total | | | 5.5104 | 11.031 | - | - | Fe-46% |
| | | | | | | | MnO-1.026% |
| Oxygen in iron as FeO | | | 0.022 | 2.77 | - | *5.54 kg of | MgO-1.16% |
| Charcoal - 30 kg | | | | | | | SO2-0.075% |
| F.C | 75.8 | | | 0.96 | - | iron will be | |
| Ash | 3.2 | | | - | - | associated with | |
| V.M. | 21.0 | | | - | - | 21 kg slag. | |
| | | | | | | Thoretical slag | |
| Total-54 kg | | | 5.5324 | 14.761 | 22.718 | wt.=14.761 kg | |
| | | | | theoretical | 6.3 | hence SiO2+Al2O3 | |
| | | | | slag wt | | | |
| | | | | | | | Theoretical | |
| | | | | | 54 kg* | | charcoal for | |
| | | | | | | | reduction=16 kg |

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conclusions. Table 8 gives the chemical analysis of some of the important iron objects and iron produced by the ancient furnaces.

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(IV.6) Process of Carburization and Wootz Steel Production

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As Kulkarni(1989) has quoted the Sanskrit text (Rgveda 9.112.2) and its Hindi translation by M.N. Banerjee(1929) the process of carbon alloying by carburization was known even in that period and the steel objects produced were sold at very high price. Hadfield(1912) has also mentioned the possibility of use of Indian iron chisels and even Indian craftsmen in building by Pyramids of Egypt.

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The Suśruta Saṃhitā has mentioned the process of carburization by applying a carbonaceous paste on the edge of the surgical knives and heating them to red hot condition, followed by hardening and tampering treatments to develop razor sharp edge (700 B.C.) which could split hair into two parts longitudinally.

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The carburization of hot sponge or bloom could be done by the following techniques:

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i) Increasing the carbon content of the hot sponge inside the smelting furnace by raising the furnace temperature and the retention time of the hot sponge for a slightly longer period.

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ii) By increasing the temperature and the time of contact between the hot iron bar and charcoal during secondary refining.

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iii) By selective carburization of cutting edge of the implements by the application of carburizing paste and reheating to 950 to 1000°C.

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Table 8 — Chemical composition of iron produced by ancient Indian furnaces

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| Insert | C% | Si% | Mn% | P% | S% | Others |
| 1. Delhi Iron Pillar | 0.23 | 0.066 | - | 0.18 | Traces | N2 = 0.0065% |
| 2. Bhubaneshwar Iron Beams | 0.27 to 0.45 | 0.05 to 0.11 | Traces to 0.04 | 0.015 to 0.018 | 0.006 to 0.015 | Cr-0.9% Ni-1.6% |
| 3. Bastar Iron Axe (100 years old) | 0.25 ot 0.45 | - | - | - | - | Other elements in traces |
| 4. Jabalpur Iron (recent) | 0.59 | 110 PPM | 40 PPM | - | - | Cu-340M Ni-353 PPM Others in traces |
| 5. Bishunpur Iron (recent) | 0.016 ot 0.043 | - | 0.057 | 0.02 to 0.2 | 0.007 to 0.013 | - |

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Varahamihira (550 A.D.) (Ray, 1956) has mentioned the following processes for carburization and hardening of iron swords:

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i) Make a paste of the gelatin from the sheep’s horn and pigeon’s, mouse’s dung with the juice of the plant Arka (Caletropis gigantica) and apply this to the steel after rubbing it with seasam oil. Heat the sword in the fire and when it is red hot sprinkle on it water or milk of horse (camel or goat) or ghee (clarified butter) or blood or fat or bile. Then sharpen the edge on the lathe (Varāhamihira *Kharaglakṣṇam*, Chap.XVIX, Śloka 23-26).

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ii) Plung the steel (high carbon), red hot into a solution of plantain ashes in whey, kept standing for twenty hours, then sharpen on the lathe.

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The iron treated by the carburizing process suffered from the structural heterogeneity and non-consistency of quality as well as low fracture strength due to high inclusion rate. These difficulties were solved by the introduction of the process of production of Wootz steel.

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(IV.7) Production of Wootz Steel

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Ball (1881) writes that the ‘Wootz’ steel was much sought in the Eastern Mediterranean countries even earlier than Christian Era. The Indian masters had realised the effect of addition of ‘C’ to iron and the excellence of the cutting edges formed on such steel weapons. Wootz steel was being produced in several places in India and exported to the West even as early as 700 B.C. for the manufacture of famous ‘Damascus Swords’. This sword had attained its reputation for edge sharpness, flexibility, strength and the typical surface structure on the sword’s surface. Fig.34 shows the typical surface structure of the sword developed by ‘Damascusizing’ and ‘watering’ treatments. Inspite of innumerable attempts made by the technician and metallurgists of the Western World this type of structure has remained a fascinating mystery. The details of these attempt have been reviewed in great detail by Piaskowski (1974), Yater (1983, 1983- 84, Thomsen (1987), Kedzierski and Stepineski(1987), Antiens (1987) and many others. Paiskowski has concluded that "Although the research on Dasamcene steel did not lead to its widespread production but the extent of interest shown by the research workers has enriched the imagination of scientists and has had a decisive influence on the development of science and technology". The latest study on the development of steel having this famous pattern has been by Verhoevens et al(1987). Raj and Sundaram (1990) have mentioned that in USA a patent has been obtained at Stanford for ‘ultra high carbon steel’ with 1.3% to 1.7% C (same as Wootz steel which has shown super plastic property along with hardness and strength and this may be produced in bulk for making the automobile and aircraft components.

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Fig. 34. Watering structure seen on ‘Wootz’ steel swords

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Bronson (1986) in his review on this celebrated steel has questioned the origin of this Indian technology and tried to give credit to Iran or other Arabian countries who were in knowledge of the qualities of this steel and considered it worth while to journey to India to procure it, but after studying the classification of Iron-Carbon alloys (communicated to him by the author) he has agreed to the origin and the production of molten steel in India. This technology was most probably developed for the first time either in Gujarat or Hyderabad. The English word ‘Wootz’ is supposed to be abbreviation of either Gujarati word ‘Wuz’, or ‘Hooku’ or ‘Ukku’ in Telugu language, which means steel or ‘Pulat’ in Persian. The other regions mentioned in the literature are Tamilnadu and Mysore where this quality of steel was made by the crucible melting technique. In the northern Indian crucibles and furnaces similar to those used in South India have been found, at Rajghat (Varanasi) and ‘Khairadih’ where most probably ‘Wootz’ steel was being produced between 600 B.C. to 1000 A.D.

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The following two distinct processes have been reported by Yater (1983, 1983-84), Bronson (1986), Prakash,B. (1987) and Rao, K.N.P. (1989).

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(i) By carburization of wrought iron rods and melting in small crucibles.

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(ii) By decarburization of white cast iron.

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In the first process steel was made by packing about 350 gms of small pieces of wrought iron into a clay crucible with 1/10th of its weight of chipped dry wood and leaves of specific plants e.g. Avaram (Casia auriculata) etc. and the crucibles mouth was sealed with clay. Fig.35 shows the branch, leaves and flowers of Casia Auriculata. Sometimes a hole was made in the crucible cover for the escape of the gases produced inside the crucible. During heating 20 to 25 or some times more number of such crucibles were heated in a specially designed furnace where the central crucible could attain a temperature of more than 1550°C. The furnace as described by Buchnan(1807) and others gives an idea how the crucibles were shifted in a fixed order to the hottest zone of the furnace where the steel reached the molten state. After this crucible was either cooled slowly or it was water quenched. The process details and the time of one such operation have been summarized by Bronson (1986). The wrought iron charge could be carburized in about 2 to 6 hours and the extent of carburization was controlled by adjusting the proportion of wood chips in the charge and the residual amount of the FeO rich slag remaining in the wrought iron.

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During the processing and melting of the steel molten slag was separated and clean steel ingot was obtained, which could be further classified and processed for the production of war weapons, tools and objects like wires for musical instruments etc. *Fig. 36* gives a macro-photograph of Wootz steel ingot published by Tylecote (1962) and *Table 9* gives some typical compositions of Wootz steel as quoted by Percy (1861) and Bronson (1986).

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The crucibles used in this process had a conical or pear shape and they were very skillfully prepared from a refractory material capable of sustaining such treatment. *Fig. 37* shows a picture of conical crucible preserved in the National Museum of Madras, and also a sketch of the same is shown in *Fig 38*. These crucibles were prepared from a range of compositions based on their end use and these have been mentioned in the ancient Ayurvedic texts *Rasa Ratna Samuccaya* and *Suśruta Samhitā*. The crucibles used for making Wootz steel generally prepared from a mixture of some silicious clay or Caoline mixed with rice husk and iron oxide sand. On firing of these crucibles in reducing atmosphere at first at 400-500°C and then at 1100-1200°C, the rice husk got charred depositing carbon and adding SiO2 to the clay. Recently Lowe et al. (1990) have analysed and studied the composition as well as structure of many such used crucibles collected from the steel melting sites of the Hyderabad region and confirmed the excellent refractoriness of these crucibles. The structure of these crucibles was found to be consisting of SiO2 phase present in a matrix of Mullite (M.P. 1800°C), some graphite particles and small prills of iron, produced by the reduction FeO present in the crucible.

First 161 of 198 passages. Read on

Linked texts (14)

Rasaratnasamuccaya — Vāgbhaṭa (alchemist), Sanskrit
Ṛgvedasaṃhitā — Sanskrit
Suśrutasaṃhitā — Suśruta & Nāgārjuna (siddha/alchemist), Sanskrit
Bṛhatsaṃhitā — Varāhamihira, Sanskrit
Harappā
Mohenjo-daro
Lothal
Atranjikhera
Nālandā
Gufkral
Naikund
Zawar
Mandla
Bisunpur