Pattern welding

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Pattern welding is the practice in sword and knife making of forming a blade of several metal pieces of differing composition that are forge-welded together and twisted and manipulated to form a pattern. Often called Damascus steel, blades forged in this manner often display bands of slightly different patterning along their entire length. These bands can be brought out for cosmetic purposes by proper polishing or acid etching. Originally, pattern welding was used to combine steels of different carbon contents, providing a desired mix of hardness and toughness. Although modern steelmaking processes negate the need to blend different steels, pattern welded steel is still used by custom knifemakers for the cosmetic effects it produces.



Pattern welding was developed in both Europe and Asia as a means of averaging the properties of iron and steel. Iron is too soft and flexible for use in weaponry, while the hypereutectoid steel produced in the ancient world was too hard and brittle. The earliest known use of pattern welding in Europe is from an 8th century BCE sword found at Singen, Württemberg in Germany (Salter & Ehrenreich 1984). The Celts originally employed alternating rods of iron and steel twisted together and then welded with the use of the bloomery furnace which can bring iron and steel (carburized iron) to a welding temperature, but not melt them. In Asia, the carbon content of the iron and steel produced in the bloomery process was highly variable, and repeated folding and welding was employed to remove excess slag and impurities from the metal and to homogenize it. Two or more batches of fairly uniform steel (each batch with a different composition) were then welded together. The different steels result in blades with improved mechanical properties and a distinctive wavy pattern being observed after etching. The technique first appeared about 300 BCE, and by 500 CE was being used by the Merovingian dynasty. Through their successors, the Carolingian dynasty, the technique became common throughout Europe by about 700 CE. The period of European pattern welding, then, encompasses the Celto-Roman Iron Age through the Migration Era. Introduction of the blast furnace brought it to an end.

By the 9th century in Europe, the blast furnace became available and with it the ability to create homogenous high carbon steel. The need for pattern welding all but died out for other than cosmetic applications. During subsequent centuries the technique was slowly lost, and by 1300 there are few examples of its use. The technique survived, however, in Scandinavia, where good quality iron ores and charcoal were widely available.

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