Author:
Publication: The Week
Date: June 24, 2001
Saladin the Saracen had a steely
edge over Richard the Lion-hearted. Sir Walter Scott, in his romance The
Talisman, describes a meeting of the two mediaeval monarchs who crossed
swords in the Crusades.
After examining an iron bar that
Richard cut in two with his sword, Saladin took a silk cushion from the
floor and placed it upright on one end. "Can thy weapon, my brother, sever
that cushion?" he said to King Richard.
"No, surely," replied the King,
"no sword on earth, were it the Excalibur of King Arthur, can cut that
which poses no steady resistance to the blow."
"Mark, then," said Saladin and unsheathed
his scimitar, a curved and narrow blade of a dull blue colour, marked with
ten millions of meandering lines and drew it across the cushion, applying
the edge so dexterously that the cushion seemed rather to fall asunder
than to be divided by violence.
Scott mentions that the sabres and
poniards of the Ayyubid troops were of Damascene steel.
The original Damascus steel-the
world's first high-carbon steel-was a product of India known as wootz.
Wootz is the English for ukku in Kannada and Telugu, meaning steel. Indian
steel was used for making swords and armour in Persia and Arabia in ancient
times. Ktesias at the court of Persia (5th c BC) mentions two swords made
of Indian steel which the Persian king presented him. The pre-Islamic Arab
word for sword is 'muhannad' meaning from Hind.
Wootz was produced by carburising
chips of wrought iron in a closed crucible process. "Wrought iron, wood
and carbonaceous matter was placed in a crucible and heated in a current
of hot air till the iron became red hot and plastic. It was then allowed
to cool very slowly (about 24 hours) until it absorbed a fixed amount of
carbon, generally 1.2 to 1.8 per cent," said eminent metallurgist Prof.
T.R. Anantharaman, who taught at Banares Hindu University, Varanasi. "When
forged into a blade, the carbides in the steel formed a visible pattern
on the surface." To the sixth century Arab poet Aus b. Hajr the pattern
appeared described 'as if it were the trail of small black ants that had
trekked over the steel while it was still soft'.
The carbon-bearing material packed
in the crucible was a clever way to lower the melting-point of iron (1535
degrees centigrade). The lower the melting-point the more carbon got absorbed
and high-carbon steel was formed.
In the early 1800s, Europeans tried
their hand at reproducing wootz on an industrial scale. Michael Faraday,
the great experimenter and son of a blacksmith, tried to duplicate the
steel by alloying iron with a variety of metals but failed. Some scientists
were successful in forging wootz but they still were not able to reproduce
its characteristics, like the watery mark. "Scientists believe that some
other micro-addition went into it," said Anantharaman. "That is why the
separation of carbide takes place so beautifully and geometrically."
Francis Buchanan and other European
travellers have observed the manufacture of steel by crucible process at
several places in Mysore, Malabar and Golconda from the 17th century onwards.
The furnace sketched by Buchanan shows that crucibles were packed in rows
of 15 inside a pit filled with ash. A wall separated the bellows from the
furnace, with only the snout of the bellows sticking out through the wall.
Each crucible could contain up to 14 ounces of iron, along with stems and
leaves.
The crucible process could have
originated in south India and the finest steel was from the land of Cheras,
said K. Rajan, associate professor of archaeology at Tamil University,
Thanjavur, who explored a 1st century AD trade centre at Kodumanal near
Coimbatore. Rajan's excavations revealed an industrial economy at Kodumanal.
A sword bit excavated from there
had a thin layer of high-carbon steel on the cutting edge. Apart from this,
there was a coating of thin white layer, probably to protect the edge from
rust!
Pillar of strength The rustless
wonder called the Iron Pillar near the Qutb Minar at Mehrauli in Delhi
did not attract the attention of scientists till the second quarter of
the 19th century.
The first reports of the pillar
were by British soldiers, and Captain Archer talked about its inscription
of 'unknown antiquity which nobody can read'. James Prinsep, an Indian
antiquarian, deciphered the inscription in 1838 and translated it into
English in the Journal of the Asiatic Society of Bengal.
Scholars consider the pillar to
be of early Gupta period (320-495 AD) on grounds of palaeography, content
and language of the inscription and the style of execution. But there are
differences in opinion over whether the king referred to in the inscription
as Chandra is Samudragupta (340-375) or his son Chandragupta II (375-415).
The pillar was perhaps a standard for supporting an image of Garuda, the
bird carrier of Lord Vishnu.
The inscription refers to a ruler
named Chandra, who had conquered the Vangas and Vahlikas, and the breeze
of whose valour still perfumed the southern ocean. "The king who answers
the description is none but Samudragupta, the real founder of the Gupta
empire," said Prof. T.R. Anantharaman, who has authored The Rustless Wonder,
a monograph published by Vigyan Prasar.
In 1961, the pillar (23 feet and
8 inches, and 6 tonnes) was dug out for chemical treatment and preservation
and reinstalled by embedding the underground part in a masonry pedestal.
Chemical analyses have indicated that the pillar was astonishingly pure
or low in carbon compared with modern commercial iron.
In 1963, M.K. Ghosh of the National
Metallurgical Laboratory concluded that the pillar had been very effectively
forge-welded. B.B. Lal, chief chemist at the Archaeological Survey of India,
also came to the conclusion that the pillar was not cast, but fabricated
by forging and hammer-welding lumps of hot pasty iron, weighing 20 to 30
kg, in a step-by-step process. The surface of the pillar retains marks
of hammer blows. It is assumed that 120 labourers took a fortnight to complete
this daunting task.
The excellent state of preservation
of the Iron Pillar despite exposure for 15 centuries to the elements has
amazed corrosion technologists. High phosphorus, low sulphur, low manganese
and high slag contents contribute individually and collectively to the
good corrosion resistance.
Besides, a protective oxide film,
50 to 600 microns thick, has formed on the pillar. This is less than 50
microns in the bright, polished section where people used to clasp around
for luck.
Galvanising feat The oldest among
the triad of metallurgical marvels of ancient India is the extraction of
zinc. Zinc is better known as a constituent of brass than a metal in its
own right. Brass with 10 per cent zinc glitters like gold.
The earliest brass objects in India
have been unearthed from Taxila (circa 44 BC). They had more than 35 per
cent zinc. "This high content of zinc could be put in only by direct fusion
of metallic zinc and copper," said Prof. T.R. Anantharaman. The other process,
which is no more in use, is by heating zinc ore and copper metal at high
temperatures, but the zinc content in brass then cannot be more than 28
per cent.
Zinc smelting is very complicated
as it is a very volatile material. Under normal pressure it boils at 913
degrees centigrade. To extract zinc from its oxide, the oxide must be heated
to about 1200 degrees in clay retorts. In an ordinary furnace the zinc
gets vapourised, so there has to be a reducing atmosphere. By an ingenious
method of reverse distillation ancient metallurgists saw to it that there
was enough carbon to reduce the heat.
Proof of the process came from excavations
at Zawar in Rajasthan. The Zawar process consisted of heating zinc in an
atmosphere of carbon monoxide in clay retorts arranged upside down, and
collecting zinc vapour in a cooler chamber placed vertically beneath the
retort.
Zinc metallurgy travelled from India
to China and from there to Europe. As late as 1735, professional chemists
in Europe believed that zinc could not be reduced to metal except in the
presence of copper. The alchemical texts of the mediaeval period show that
the tradition was live in India.
In 1738, William Champion established
the Bristol process to produce metallic zinc in commercial quantities and
got a patent for it. Interestingly, the mediaeval alchemical text Rasaratnasamucchaya
describes the same process, down to adding 1.5 per cent common salt to
the ore.
