The pillar of Ashoka: the amazing metallurgic art of the ancient Indians
In Delhi, India, there is a surprising iron column which, despite having passed at least 15 centuries since its creation, shows no signs of rust and is so impenetrable to corrosion that modern technology is unable to match its structure.
The so-called Iron Pillar (or Ashoka Column), located in Delhi (India), is an iron column 7 meters and 21 centimeters high, weighing 6 tons and with a diameter of 41 centimeters. The column dates back to at least 423 AD and has no rust despite having been exposed to the monsoon climate for 1600 years.
It was probably built by Chandragupta II Vikramaditya (375 AD – 414 AD), during the Gupta empire which reigned over northern India between the 4th and 6th centuries.
The pillar originally stood at a place called Vishnupadagiri (Vishnu's footprint hill). During the Gupta Empire, Vishnupadagiri was a center of astronomical studies, as the hill was located on the Tropic of Cancer. The pillar cast a shadow, which on the summer solstice (June 21) fell in the direction of Anantasayain Vishnu's foot.
Later, when Qutb-ud-din Aibak destroyed the pre-existing temples to erect the Qutb Minar and the Quwwat-ul-Islam mosque, the Ashoka Pillar was left intact, and the mosque was developed around it. On the column there is an inscription according to which it was built in honor of Vishnu and in memory of King Chandragupta II.
The enigma of the column
Given its particular resistance to rust and corrosion, the Ashoka Pillar is the object of interest of numerous scholars. Furthermore, its peculiar characteristics have led many to consider it as an OOPArt, that is, an inexplicable object in its original historical context. Why?
As revealed by a study carried out by Professor A. G. Gupta, director of the Department of Applied Sciences and Philosophy at the Indian Institute of Technology and Management, the pillar is made of 99.72 percent pure iron.
To give you an idea, the iron obtained in the modern era is obtained with a purity of 99-99.8 percent, and contains manganese and sulfur, two ingredients absent in the pillar. The column is also covered in a protective oxide patina, making it unlike anything else produced today.
Thanks to its particular composition, the column has survived intact for more than 1500 years exposed to atmospheric agents, without showing the slightest sign of oxidation or corrosion.
The analyzes of experts from the Indian Institute of Technology, led by Professor R. Balasubramaniam, have shown that it is a particular property of the metal it is made of, a very pure iron, with an unusually high percentage of phosphorus due to a particular casting technique created by the artisans of the time.
Over time, the phosphorus would have favored the formation by catalysis of a protective layer on the surface of the column, a compound of iron, oxygen and hydrogen 5 hundredths of a millimeter thick capable of protecting the soft iron from the aggression of the atmosphere.
A study by John Rowlett reveals that the pillar was made at least 400 years before the creation of the largest foundry known in the ancient world and which could have made the column.
To underline the early metallurgical expertise of the Indians of 15 centuries ago, Rowlett recalls the case of the Sultanganj Buddha, the largest Indian metal sculpture of Buddha.
Also made 1500 years ago, made of pure copper and weighing more than a ton, as Rowlett writes, “no scientific explanation has yet been put forward as to how such a work could have been made at such an early period”.
The statue, a disconcerting reminder of the extraordinary skills of the sculptors and metal craftsmen of ancient India, has survived practically intact for 15 centuries, making it unique in the world.
