Wednesday, April 27, 2016

The steel from Serendib.

Damascus, an ancient city with a history running back almost 6000 years before Christ... A city of magic and romance, where civilizations met, displayed their wares, traded, haggled, clashed their swords and sometimes mingled. Damascus is a city which had seen innumerable wars and battles. It had seen the rise and fall of many empires. It had embraced numerous gods only to forget them in due time and worship new gods.
And one legend which still abounds about this city in the near East, is its swords. The Damascus swords had been and still continues to be an object of much speculation. The legendary swords with their blades with the well known rippling pattern, resembling that of flowing water or soft rippling fabric, was a legend.... a mystery..
Stories were abound about the sharpness and the plasticity of the blade. Legends has it that the sword could cut with precision through the barrel of a rifle and through a hair falling across it's blade. It could go through many a battle and slash through bone and flesh and still retain its sharpness. Legends has it that the blade of Saladin himself was of Damascus steel.
The secret of Damascus sword lies in the steel that was used to forge it.
And the story begins many miles due east, in southern India and especially in a small island that they called Serendib.
"..the finest steel for Damascus blades came from Serendib.."
Sri Lanka, as 'Serendib' is better known now, started exporting high quality steel somewhere in the 1st century AD, the production reaching its zenith during the 9th century AD. But how did the ancient Sri Lankans make such fine steel?
The iron age started in Sri Lanka in 1000BC. Little by little Sri Lankans learned to smelt iron from iron containing ores. Initially they used bloomeries, which produced only low carbon high impurity iron of unremarkable quality. But later on they progressed on to use blast furnaces where the stream of air was supplied by bellows.
In Sigiriya, sri Lanka, remains of such ancient blast furnaces have been found. The bellows were made of animal skin and placed in clay containers and an operator work them to keep a constant supply of air.
Blast furnaces developed all over the world and could be defined as the climax of the iron age. Better quality iron with a higher percentage of carbon could be produced this way.
But in Sri Lanka, unlike other areas, high carbon, low impurity steel was being produced even before they had perfected the blast furnace!! So what is the secret?
The discovery was made in a perfectly providential manner in 1988. That year the then reigning government of Sri Lanka embarked on a hydroelectric project centered in the Walawe river basin in Southern Sri Lanka. It involved the construction of 'Samanalawewa Dam' across the Walawe river. The area was not a known archeological site, but an initial field survey revealed a unique archeological discovery.
It was an iron smelting furnace located on the western slopes of the hills, facing south west. Further research revealed almost 80 such sites. Surveys suggested that at one time there could have been almost 3000 smelters in this area.
The furnaces were unique in the true meaning of the word. They were not bloomeries and neither were they blast furnaces.
In fact they were wind driven, actually monsoon wind driven furnaces.
From June to September, monsoon winds sweep inwards to the island from the vast expanse of the Indian ocean. These furnaces took the natural advantage of the monsoon winds to supply a continuous stream of air.
At least one site from 'Samanala wewa' was from as far back as the 3rd century BC. It can be definitely stated that steel of highest quality with low impurities and high carbon percentage was being produced by the 1st century AD. And that is the earliest evidence of high quality steel from south Asia, according to Dr. Jill Julef.
The furnaces were easy to work, because unlike blast furnaces, they required comparatively little man power. So they were cost and energy efficient.
The technical details of the furnaces are also impressive and suggest the broad technical knowledge possessed by the ancient engineers.
Wind, close to the ground level blowing uphill, would reach maximum velocities at the crest, where the furnaces were located. The front wall of the furnace acts as a barrier and splits the stream of air into two layers. The stream that flows up over the top of the furnace roof creates an area of low pressure, which effects the lower layer of air to be sucked into the furnace through the tuyere at the front.
The maximum efficacy of the furnace, depends on the laminar airflow along the tuyere. The airflow has to be in the transition zone between laminar to turbulent. To make sure that this requirement is met, the physical variable called the Reynolds number has to be within a certain range. If we are modern day physicists with complex computation devices we would have to use certain complicated equations to find out the right tuyere diameter and angle to give the appropriate flow speeds assuming that the monsoon wind speeds are more or less fixed.
But more than 2000 years ago the ancient Sri Lankan craftsmen also knew the diameter and the angle which was optimal. It is extraordinary that the modern calculated values of those variables and the actual measurements taken in the field, match together beautifully...
Actual working replicas of the furnaces made by archeologists had been so efficacious that they are presumed to have produced about 10 tons of steel each year.
The carbon source for thus produced steel came from plant material incorporated whilst being produced. This was also different from the more widespread practice of using charcoal as a source for carbon.
Investigations into Damascus steel conducted as recently as 2006 have revealed the presence of carbon nanotubes encasing cementile nanowires. Some specialists claim that this unique nanowire and tube arrangements may have arisen due to the use of plant material for a carbon source.
Steel production in sri Lanka reached its zenith by the 9th century AD. Its reputation as an exporter of the finest steel in the world was well documented in the Islamic world.
But this unique method of steel production seems to have disappeared from the Sri Lankan history by the 11th century AD. This archeological fact may be accounted for by the gradual decline of the ancient rajarata civilization which culminated in the invasion and the subsequent carnage of Kalinga Maga in 1215....
Damascus steel continued to be produced from the steel from south India. But after about 1700 AD, the craft declined until it became another one of the lost arts of the ancient world....

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