Damascus steel originally referred to swords that were made in the Middle East from the late Middle Ages to the early Modern Era, though contemporary uses of the term may include objects created with reproduction techniques. Swords made with Damascus steel had a reputation of being strong and resilient, and could be identified by the water-like patterns that covered the blades. The exact alloy used to create Damascus steel, along with the process that resulted in the unique markings, is no longer known. Examination of these ancient blades has revealed the presence of advanced structures, such as carbon nanotubes. A variety of modern techniques have been used to create replicas, with varying levels of success.
It is thought that swords of Damascus steel were largely constructed from wootz steel, which was imported from India as ingots. Wootz steel was formed by combining iron, charcoal, and glass in a sealed crucible. This type of crucible steel was known for its characteristic banding pattern, which revealed the presence of pearlite or martensite matrices that contained hard micro carbides. The presence of these carbides may have been one of the main contributing factors to the unique qualities of Damascus steel, though it is likely that trace impurities, such as vanadium or tungsten, played a role as well.
The process of turning wootz steel ingots into Damascus steel blades is not well understood, as the technique was no longer used after about 1750 CE. Historians are also unsure of why the technique fell out of favor, though it is thought that there may have been trade difficulties in procuring sufficient quantities of wootz steel. There may also have been some small change in the production of wootz steel that could have resulted in a lack of certain trace impurities necessary for the success of the Damascus techniques. A specific combination of trace impurities and thermal cycling of the forged blades was likely required to create the unique damask pattern.
Modern reproduction techniques focus on the use of either forged crucible steel or pattern welded steel. Pattern welding can create a similar visual effect of rivulets like that seen in Damascus steel, so it was traditionally thought that such a method had been used. Research suggests that other techniques were likely used instead, though modern reproductions using pattern welding are often marketed as Damascus steel. Other reproduction techniques have focused on the use of bulat steel from Russia, which may have similar characteristics to Indian wootz steel from the Middle Ages.