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== Extraction Process in Ancient Times ==

== Extraction Process in Ancient Times ==

Iron ores were widely distributed in Indian subcontinent. However they were delayed to smelt Iron. The reason is that the primitive condition of furnace has produced temperature about 1100°C which is required for Copper smelting. But Iron needs a high temperature almost above 1500°C for the ore to smelt into a liquid. Little solid grains of Iron have obtained by low temperature as 800°C. Iron is a soft and spongy material which had to be admixed with carbon in proper proportion to obtain sufficient sharpness and hardness. It was obtained from ores at high temperature. Iron has more impurities than Copper. This impurity is removed by using a catalytic flux such as lime to produce the slag (Rao 1970:258). Iron produced by smelting is of 3 kinds:  

Iron ores were widely distributed in Indian subcontinent. However they were delayed to smelt Iron. The reason is that the primitive condition of furnace has produced temperature about 1100°C which is required for Copper smelting. But Iron needs a high temperature almost above 1500°C for the ore to smelt into a liquid. Little solid grains of Iron have obtained by low temperature as 800°C. Iron is a soft and spongy material which had to be admixed with carbon in proper proportion to obtain sufficient sharpness and hardness. It was obtained from ores at high temperature. Iron has more impurities than Copper. This impurity is removed by using a catalytic flux such as lime to produce the slag. Iron produced by smelting is of 3 kinds:  

* wrought iron (Kanta Loha)

* wrought iron (Kanta Loha)

* carbon steel (Tikshna Loha)

* carbon steel (Tikshna Loha)

Quenching and tempering was also learnt along with steeling of Iron. Quenching consists immersing the red hot metal into water. Metal would become hardened by this process. Tempering consists of repeated heating of the metal and allowing it to cool slowly while it is hammered (Banerjee 1965:2).<ref>Saravanan, R. ''Iron:'' ''From Metal to Metallurgy'' Heritage: Journal of Multidisciplinary Studies in Archaeology 5 (2017): 514‐518</ref> Raw iron, wood and carbon are heated in earthen bowls at a temperature of 1535°C and then, slowly cooled over 24 hours. This gives high quality carbon rich steel. A sword made of this steel is so sharp and strong that it even cuts silk smoothly.  

Quenching and tempering was also learnt along with steeling of Iron. Quenching consists immersing the red hot metal into water. Metal would become hardened by this process. Tempering consists of repeated heating of the metal and allowing it to cool slowly while it is hammered.<ref>Saravanan, R. ''Iron:'' ''From Metal to Metallurgy'' Heritage: Journal of Multidisciplinary Studies in Archaeology 5 (2017): 514‐518</ref> Raw iron, wood and carbon are heated in earthen bowls at a temperature of 1535°C and then, slowly cooled over 24 hours. This gives high quality carbon rich steel. A sword made of this steel is so sharp and strong that it even cuts silk smoothly.  

 

The ancient process of iron making has been vividly described in the folk songs of `Chokh Agaria' from Lapha. One of these songs as translated by Joshi is as follows:<ref name=":2" /><blockquote>''She presses down the bellows with the strength of her heels,'' ''He wields the heavy hammer with all his might''

The ancient process of iron making has been vividly described in the folk songs of `Chokh Agaria' from Lapha. One of these songs as translated by Joshi is as follows:<ref name=":2" /><blockquote>''She presses down the bellows with the strength of her heels,'' ''He wields the heavy hammer with all his might''

## Fosse type where the furnace is of shaft type and completely subterranean i.e, constructed below the ground level by digging a small cylindrical pit or shaft as shown in the figure. Bowl type furnaces were also constructed.  

## Fosse type where the furnace is of shaft type and completely subterranean i.e, constructed below the ground level by digging a small cylindrical pit or shaft as shown in the figure. Bowl type furnaces were also constructed.  

## Aerial type furnace is where the furnace is partly subterranean and constructed over a rectangular pit.

## Aerial type furnace is where the furnace is partly subterranean and constructed over a rectangular pit.

# Making and fixing the bellows: Bellows were made of buffalo hide. The blow pipes used were of bamboo. Furnace hearth was prepared by lining it with 'Kodon' paddy chaff or charcoal powder mixed with clay. One clay pipe is inserted through a parabolic opening in the bottom of the furnace which acts as a tuyere. The opening through which the tuyere is introduced is then luted with clay.  

# [[File:Line diagram of the bellow assembly.png|thumb|403x403px|Line diagram of the bellow assembly]]'''Making and fixing the bellows''': Bellows were made of buffalo hide. The blow pipes used were of bamboo. Furnace hearth was prepared by lining it with 'Kodon' paddy chaff or charcoal powder mixed with clay. One clay pipe is inserted through a parabolic opening in the bottom of the furnace which acts as a tuyere. The opening through which the tuyere is introduced is then luted with clay.  

# drying, firing and operating the furnace.

# '''Drying, firing and operating the furnace''': After the dried furnace and the raw material were ready the furnace was charged with dried wood chips and then filled with charcoal up to the top. A ritual pooja and havan were performed praying for the successful operation of the furnace and then it was ignited using a little of the sacred fire from the havan. This was introduced inside the furnace through the tuyere pipe. When the wood starts burning, the bellows were operated slowly to build the fire inside the furnace. After the yellow flame appeared at the mouth of the furnace the blowing rate was increased to raise the furnace temperature. As the charcoal got consumed, ore was charged and the blowing was continued till a translucent blue flame appeared at the top. Blue flame indicated that the furnace reached a temperature of > 1000^oC and the charcoal is burning to generate CO gas. At this stage the furnace was charged with alternate layer of ore and charcoal in the ratio 1:2 and the air blowing rate was adjusted and controlled to maintain steady condition. The temperature inside the furnace was visually examined by peeping through the tuyere pipe and after about one hour the first slag was tapped. The fluidity .of the slag, its quantity as well as colour on solidification were indicators of successful operation of the furnace. The slag was either tapped periodically or continuously throughout the furnace operation. When sufficient charges of ore had been made, it was followed by few blank charges of charcoal only, and the air blowing rate was increased to consolidate the reduced iron into a large porous lump and separate it from the FeO rich fayalite (2FeO.SiO₂) slag. The measured temperature at this stage was found to be 1500°C in front of the tuyere. One round took about 5 to 6 hours and preparation is made to take out the hot iron sponge.

# removal of slag and handling of red hot sponge iron bloom.

# '''Removal of slag and handling of red hot sponge iron bloom''': In case of bowl furnaces, generally the slag was allowed to get collected and solidified at the bottom of the furnace. In the case of other furnaces, it was tapped out through the slag hole known as 'Hagan.' After the smelting period was over, the bellows along with blow pipes were removed and the temporary wall for closing the front opening was removed and the partially melted tuyere was taken out with the help of a tong and a wooden pole. It was placed on a large granite stone anvil and hammered to consolidate and remove the molten slag filled in the pores.

# secondary refining of the bloom.

# '''Secondary refining of the bloom''': This most important and exclusive Indian practice was carried out to remove the slag trapped inside the iron block. For this, the iron bloom was reheated in a smithy forge to almost white hot (>1250°C) condition and silica sand was sprinkled upon it. This reacted with the remaining FeO and helped in forming fluid 2FeO.SiO₂ slag which flowed out of the iron block. The iron block was taken out of the furnace and forged to increase its density. This process was repeated till the bloom was converted into 12 to 15mm square/circular rod. This refined rod containing 0.2 to 0.4% SiO₂ almost free from the slag inclusion was cut into 150 to 180mm long pieces and sold to the blacksmiths or 'Lohars' for reshaping them into useful objects.

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== References ==

== References ==

[[Category:Shastras]]

[[Category:Shastras]]