The 1600 year old rust-free Iron Ashoka Pillar
The Ashoka Pillar stands almost seven metres high and weighs more than six tonnes. The pillar bears an inscription which states that it was erected as a flagstaff in honor of the Hindu god, Vishnu, and in the memory of the Gupta King Chandragupta II (375-413).
Made up of 98% wrought iron of impure quality, it is 23 feet, 8 inches high and has a diameter of 16 inches. It has attracted the attention of archaeologists and metallurgists as it has withstood corrosion for the last 1600 years despite harsh weather.
Only in 2002 Metallurgists at Kanpur IIT discovered that a thin layer of 'misawite' - a compound of iron, oxygen and hydrogen (looks like the possible work of a form of Brown's Gas!?), has protected the cast iron pillar from rust.
The protective film took form within three years after erection of the Ashoka pillar and has been growing ever so slowly since then. After 1600 years, the film has grown just one-twentieth of a millimetre thick, according to R. Balasubramaniam of the IIT.
In a report published in the journal "Current Science" Balasubramanian says the protective film was formed catalytically by the presence of high amounts of phosphorous in the iron, as much as 1 per cent against less than 0.05 per cent in today's iron.
The high phosphorous content is a result of the unique iron-making process practiced by ancient Indians, who reduced iron ore into steel in one step by mixing it with charcoal.
The pillar is a testament to the high level of skill achieved by ancient Indian iron smiths. It was erected by Kumara Gupta I of the Gupta dynasty that ruled northern India 320-540. The pillar was originally located in the temple of Muttra, with the idol of Garuda at the top. It is the only piece of the Hindu temple remaining, which stood there before being destroyed by Qutb-ud-din Aybak to build the Qutub Minar and Quwwat-ul-Islam mosque. Qutub built around it when he constructed the mosque.