Damascus Steel: Understanding the AlchemyThe legendary sword known as the Damascus steel intimidated the European invaders into the 'Holy Lands' of the Islamic civilization throughout the Crusades (AD 1095-1270). Blacksmiths in Europe attempted to match the steel, using the pattern welding technique of alternating layers of steel and iron, folding and twisting the metal during the forging process. (Pattern welding was a technique used by swordmakers from around the world, including Celts of the 6th century BC, Vikings of the 11th century AD and the 13th century Japanese.) In some cases, the European blacksmiths etched the blade or overlaid the surface of the blade with silver or copper filigree to imitate the characteristic watery lines of the Damascus steel blade. Some scholars credit this search for the Damascus steel process as the origins of modern materials science. But the European blacksmiths never duplicated the solid core Damascus steel, and the secret of its construction was lost even to the Islamic blacksmiths in the mid-18th century.
Wootz Steel and Saracen BladesWhat is known today about "true" or "oriental" Damascus steel is that it was made from a raw material called wootz steel. Wootz was an exceptional grade of iron ore steel first made in southern and south central India and Sri Lanka perhaps as early as 300 BC. Wootz was extracted from raw iron ore and formed using a crucible to melt, burn away impurities and add important ingredients, including a high carbon content (nearly 1.5% by weight---wrought iron typically has carbon content around .1%).
The high carbon content is the key--and the achilles heel--in the manufacturing process. High carbon content makes the keen edge and its durability possible; but its presence in the mixture is almost impossible to control. Too little carbon and the resulting stuff is wrought iron, too soft for these purposes; too much and you get cast iron, too brittle. If the process doesn't go right, the steel forms plates of cementite, a phase of iron which is hopelessly fragile. Somehow, Islamic metallurgists were able to control for the inherent fragility and forge the raw material into fighting weapons, an ability that somehow was lost in the mid-18th century.
But the problem is: it doesn't really make any sense that blacksmiths would lose such a useful technology. Since the knowledge of the forgers has been lost many researchers have sought it, and in fact this report is based on their findings over the past decade or more. But in a recent article in Nature, a research team led by Peter Paufler at the University of Dresden report that they may have an idea of the mechanics of how the high carbon steel was created and why it disappeared. That idea lies in that most modern of materials sciences: nanotechnology.
Nanotechnology and Medieval Sword MakingThe word 'nanotechnology' might seem a little odd to be applied to a technology that is clearly several centuries old, doesn't it? After all, a 'nanometer' is something that means one billionth part of meter, something no one could have measured until very recently. But in this sense, nanotechnology refers to the purposeful (and accidental) inclusion of very very tiny amounts of materials to create chemical reactions at the quantum level. Nanotechnology played a role in the mixing of Maya blue, that amazing color in Maya murals from 8th century America. Stained glass windows from the European Renaissance, colored glasses in Bronze Age Egypt, and violins from the 18th century master Stradivari all benefited from the creative use of tiny amounts of inclusions of foreign matter placed into created objects, creating quantum level qualitative changes in the product. Nanotechnology then is alchemy in its most pure form.
And so, nanotechnology--the inclusion of tiny amounts of foreign matter into a smelted iron product--had a crucial role in the construction of the Damascan blade. But... what were those elements and how did they get in there? The secret alchemy of making a Damascan blade was lost by the middle of the 18th century. European blacksmiths before then, and all those who came before the end of the last century who attempted to make their own blades failed to overcome the problems inherent in a high-carbon content, and could not explain how ancient Syrian blacksmiths achieved the filigreed surface and quality of the finished product.
Damascan Steel and Electron MicroscopyWhat the research team led by Paufler has done has been to use current nanotechnology to examine the microstructure of a Damascan blade using a scanning electron microscope. Investigations have determined that there are two pieces involved to this puzzle: both inclusions into the raw ore itself and the forging process completed in the mideast. Known purposeful additions to Wootz steel include the bark of Cassia auriculata (used in tanning) and the leaves of Calotropis gigantea (a milkweed). Microscopy has also identified tiny amounts of vanadium, chromium, manganese, cobalt, and nickel, and some rare elements, traces of which came from the mines in India.
These materials were already in the raw steel, but what Paufler and associates also identified in the steel were quantum level changes made in the metal which must have occurred during manufacture. They postulate that during the smith's cyclic heating and forging processes, the metal developed a microstructure called 'carbide nanotubes', extremely hard tubes of carbon that are expressed on the surface and create the blade's hardness. Thus, by blending the unique characteristics of Wootz steel with a forging process that included tiny amounts of specialized materials, the blacksmiths of the Islamic Civilization were able to create the Damascan steel. What happened in the mid-18th century was that the chemical makeup of the raw material altered--the minute quantities of one or more of the minerals disappeared, perhaps because the particular lode was exhausted. Such a difference would not have been apparent to the blacksmith visually; but, interestingly, the blacksmiths may have extended the life of the process by including small pieces of the previous batch in each new batch.
We modern archaeologists like to say that the elite stuff, the expensive goods that were restricted to the upper classes, really have no interest to us. But cracking the code of how metallurgists made the elite Damascus steel! I vote for that.
- Damascus Steel, this article and sources
- Ancient Weapons
- Medieval and Renaissance Archaeology
- History of the Crusades