Though science and technology in the modern era have accomplished things that our ancestors couldn’t even dream of, it is still worth remembering that the ancients weren’t dummies. Through a combination of ingenuity, observation, determination, and probably a lot of luck, these people managed to develop a number of surprising technologies — many of which have been lost to history and have proven surprisingly hard to reproduce today. Among these lost inventions are Nepenthe, an ancient Greek antidepressant, Greek fire, an early Byzantine version of napalm, and Roman concrete.
Last week, a tweet by Dr. Rubidium drew my attention to research on another mysterious ancient technology — Damascus steel. Renowned and practically legendary for its strength, flexibility, and ability to retain a sharp edge, Damascus steel was forged into weapons and armor in the Middle East from roughly 300 B.C.E. to 1700 C.E. The precise technique of its forging was lost, but many of the weapons survive. In 2006, researchers at Technische Universität Dresden performed an analysis of a piece of Damascus steel and found that it contains traces of very state of the art modern nanotechnology! Could this be the secret of the steel’s strength?
The paper is old, in blog terms — five years — but is fascinating and provides some interesting scientific food for thought. For those reasons, I thought I would take a look at what we know of Damascus steel and what revelations the modern study brings.
Kunimund hurled his hunting-spear behind him, shivering therewith a young fir, which, groaning, fell cleft asunder on either side. Then from under the lion’s skin he drew his glittering Damascus sword inlaid with gold, and he said, ” Does this please thee, my warlike hero?”
“Not so well as this blade,” said the chief, as he made the bright flashes of his drawn sword gleam up and down in the sunshine.
“Oh, if thou thinkest that!” cried Kunimund; “but behold how my Damascus blade shines as it cuts the air.” And as he waved the noble sword to and fro with motions of ever-varying swiftness, it seemed as if the gold inlaid upon the dark steel were turned into flashes of lightning; and, looking on it with delight, Kunimund called out between each mighty stroke, ” Do they not resound? do they not glitter?”
“They resound—they glitter!” cried the chieftain, transported in the ardour of his chivalry by these flashes; and springing from his horse, he placed himself opposite his strange companion, drawing his sword without farther question. According to the honourable ancient custom of Frankish knights, his followers stood still, awaiting the issue of their leader’s combat.
The bright sword and the glittering Damascus blade met clashing several times, each one wielded by a knightly hand, when suddenly Kunimund shouted ” Hold!” But he said it not as if calling on his foe to spare him; he spoke to his own sword, which he quickly drew back from the chieftain, who lay prostrate on the ground from its force. He tried to rise in noble knightly wrath, but he could not. A broad stream of blood pouring from the riven coat of mail, worn in vain to protect his breast, made him fall back powerless in the red pool. “Truly that was in earnest,” said Kunimund, looking on the fallen warrior with a melancholy smile.
From Wild Love: A Romance, by La Motte-Fouqué (1845).
As the above quotation illustrates, Damascus steel — and the weapons forged from it — has had an enduring hold on the imagination of authors and swordsmiths. The blades were legendary by the time of the Crusades, and almost supernatural in strength and flexibility. One can imagine that many legends of magic swords have their roots in the Middle Eastern weapons.
Adding to their mystique is their unique, beautiful patterning. Unlike the polished steel weapons used in Western nations at the time, Damascus steel is dull, and possesses an almost fluid, wavy surface.
Detail of a 16th century Iranian Damascus sword (source).
Contemporary Western smiths were unable to reproduce the material properties of the weapons, and once the technique was lost, it became the obsession of many scientists and hobbyists to rediscover it.
For instance: in 1805, we have “An account of an experiment to imitate the Damascus sword blades,” by one James Stodart, published in A Journal of Natural Philosophy, Chemistry, and the Arts*. Stodart’s attempts were evidently less than successful:
Being eager to witness some proofs of excellence and beauty which my expectation had anticipated, I too hastily and without due consideration proceeded to harden it by heating and quenching in water; and had the misfortune to see it cracking in seven or eight different places. I have no doubt this was occasioned by the unequal expansion and subsequent contraction of the different parts of the mass.
Others’ efforts were apparently more fruitful: the June 1939 issue of Popular Science includes the article, “Hobbyist creates modern swords of Damascus,” which describes the seemingly successful attempts of a dentist, Dr. W. Stuart Barnes:
Through many years, Dr. Carnes studied and experimented. He tried various combinations of carbon with iron, in an attempt to produce the required blade. He could, without much trouble, make a sword blade with an edge so keen that it would shave the most wirelike hair like a razor, or one so flexible that it could be bent double; but to combine these two qualities in the same blade was another problem.
A problem that Carnes claimed to have overcome, as the accompanying photograph shows.
Photo from Popular Science of Dr. Carnes with his home-made Damascus blade. The original caption reads, “Dr. W. Stuart Carnes proves that his modern sword of Damascus meets one of the tests of the legendary weapons. At right, shaving hair from the arm.”
The mystery of Damascus steel goes beyond the lost forging techniques, however. It is known that Damascus steel weapons were produced from steel made in India, where it is known as “wootz”. This wootz was traded to Persians, who then forged it into the infamous weapons. The final product, however, had a very high carbon content, between 1.5 to 2 percent, and high carbon steels are generally assumed to be brittle when the carbon content is within this range — quite the opposite of the properties of Damascus steel! Evidently something else was playing a role in Damascus weapons that resulted in its surprising properties.
The chemical properties of wootz were investigated** by none other than the great physicist Michael Faraday in 1819, when he was still a relatively unknown technician. Faraday speculated (incorrectly) that the steel was bolstered by the presence of small amounts of silica and aluminum. However, his speculations led a French researcher, Jean Robert Bréant, to correctly deduce in 1821 that carbon is a necessary ingredient to give the steel its strength. The reasons for this strength, however, was unknown.
Modern attempts to replicate the steel’s strength and pattern, by scientists armed with better chemical and atomic knowledge, have been more successful. In 1985, researchers Sherby and Wadsworth shed some light on the mystery of the forging process.*** They noted that the high carbon content of wootz results in a lower melting point of the metal. Using lower temperatures, Sherby and Wadsworth were able to produce strong steels with patterning comparable to that of Damascus blades. This explained, in part, the failure of Medieval Western smiths in forging Damascus weaponry; the higher temperatures of the Western forges would have destroyed any carbon structures that might give the metal its strength.
Still, a good understanding of the remarkable mechanical properties of the metal remained elusive. In 2006, however, researchers at the Institut fur Strukturphysik at the Technische Universität Dresden published the results of their own detailed investigations. They obtained a small sample of a Damascus sabre from the Berne Historical Museum in Switzerland, and inspected it using high-resolution transmission electron microscopy. An electron microscope, which uses electrons rather than light particles (photons), can resolve images of objects that are smaller than a nanometer (a billionth of a meter).
Remarkably, they found the presence of so-called carbon nanotubes, a material that is on the cutting edge of nanotechnology!
Before I describe the properties of carbon nanotubes, it is worth noting that carbon in general is perhaps the most remarkable atomic element in nature. Not only is it one of the fundamental building blocks of life (the human body is 18% carbon by mass), but it can possess a stunning variety of structural and material properties. Carbon can form diamond, which is highly transparent and the hardest material substance known, but it can also form graphite, which is almost perfectly opaque and soft enough to be used as pencil lead.
On a molecular level, the 20th century led to the revelation that carbon can take on a number of unusual forms with remarkable and potentially useful properties. In 1985, a group of researchers at Rice University prepared a new carbon structure known as a “bucky ball“, a collection of 60 carbon atoms that form a shape like a soccer ball.
The molecule known as “Buckminsterfullerene” or a “bucky ball”, C60. Named after Buckminster Fuller, the developer of the geodesic dome (image source).
The unique properties of such bucky balls suggests their use in a number of nanoscale applications. For instance, it has been shown that they can be used to trap single molecules, allowing unique opportunities for chemical study. The discoverers of bucky balls — Curl, Kroto and Smalley — won the 1996 Nobel Prize in chemistry for their achievement.
A more recent Nobel Prize was awarded for the discovery of another important and remarkable carbon structure, known as graphene. Graphene is a single atom thick layer of carbon atoms arranged in a honeycomb lattice, which has been referred to as an “atomic scale chicken wire”.
Visualization of the structure of graphene. Each sphere represents a carbon atom (image source).
The two-dimensional structure of graphene gives it unique mechanical and electrical properties, and it is already being groomed as the electronic material of the future. Researchers Geim and Novoselov won the 2010 Nobel Prize in Physics for their research on graphene, which includes producing it by peeling tape off of graphite!
A carbon nanotube is in essence a piece of graphene rolled into an ultrathin tube. Carbon nanotubes typically have a diameter of roughly a nanometer (billionth of a meter), but have been grown up to 18 centimeters long! They first became popular due to pioneering research done in 1991, but in fact had been observed as far back as the 1950s, though this early work apparently drew little attention.
An illustration of a carbon nanotube (image source).
Carbon nanotubes possess unusual electrical properties, similar to graphene, and have many potential applications in electronics. It is their mechanical properties that really stand out, however — multi-walled carbon nanotubes (tubes within tubes) can have a tensile strength roughly fifty times greater than steel, at a much lower density and with significant flexibility.
The strength of carbon nanotubes has led them to be researched for a number of applications, from the practical to the fanciful. On the practical side, macroscopic weaves of such tubes could form the basis of new bulletproof vests. On the speculative side, the possibility of fabricating nanotube cables makes a space elevator feasible!
A space elevator is a concept that sounds like pure science fiction but is seriously being considered. A cable is strung from a station on the Earth’s equator to a counterweight in orbit, balanced so that the center of mass of the system is in geosynchronous orbit at some 36,000 km. The cable will remain stretched, thanks to the centrifugal force on the counterweight, and the cable will remain perpendicular to the Earth’s surface due to the geosynchronous position of its mass. An ascension vehicle can then crawl up the cable, bringing things into orbit in a few days without a need for a dangerous rocket trip.
One of the biggest obstacles to such a scheme is the existence of a cable strong enough, light enough, and flexible enough to withstand the forces exerted upon it. It so happens that a cable made out of carbon nanotubes would meet all of these requirements, and could conduct electricity to the ascension vehicle, also! The downside: nobody knows as yet how to fabricate a 36,000 km long cable of carbon nanotubes.
The presence of single and multi-walled carbon nanotubes in Damascus steel would seem to explain the steel’s legendary properties: both the steel and the nanotubes are renowned for their flexibility and strength. In addition to the carbon nanotubes, the Dresden group discovered remnants of nanotubes of iron carbide (cementite) in the Damascus steel. Though such cementite is typically brittle, as high-carbon steel is expected to be, the evidence suggests that carbon nanotubes might encapsulate and protect the cementite tubes from damage.
It is certainly very surprising to find carbon nanotubes in Damascus steel, but their presence alone does not prove that they are responsible for the steel’s mechanical properties. There does not seem to have been significant follow-up research on the subject, no doubt in large part due to the difficulty in acquiring samples of the steel.
It is quite fascinating to imagine, however, that ancient Mideast swordsmiths may have inadvertently taken advantage of a nanotechnology that would not be appreciated by modern science until hundreds of years later.
* J. Stodart, “An account of an experiment to imitate the Damascus sword blades,” Journal of Natural Philosophy, Chemistry, and the Arts 7 (1804), 120.
** M. Faraday, “An analysis of Wootz, or Indian steel,” Quarterly Journal of Science, Literature, and the Arts, 7 (1819), 288.
*** O.D. Sherby and J. Wadsworth, “Damascus steels,” Sci. Am. 252, issue 2 (1985), 112.
Reibold, M., Paufler, P., Levin, A., Kochmann, W., Pätzke, N., & Meyer, D. (2006). Materials: Carbon nanotubes in an ancient Damascus sabre Nature, 444 (7117), 286-286 DOI: 10.1038/444286a