The technique of producing a pattern on a blade or other ferrous artefact by the welding together of two or more types of iron or steel.
From the second century AD some Roman swords were made with a patterned core fabricated by twisting and welding together several rods of low carbon iron and phosphoritic iron. Steel cutting edges were then welded on to this complex composite core. The resulting complete blade would be etched to reveal the complex pattern of welds. It is likely that these blades were regarded as high status objects, considering it would have taken about 70 hours to manufacture a sword (Anstee & Biek), and that they were recorded as being given as gifts. Even so, it is likely that they were mechanically inferior to a weapon made with a plain low-carbon iron core as examination of the swords has revealed that the welds were often poorly executed, with many slag inclusions, and even voids, at the welds between the various decorative components (Tylecote & Gilmour 1986, Gilmour and Salter 1998).
In the early period the cutting edges do not appear to have been hardened, but later the cutting edges were quenched. By the tenth century the number of pattern-welded swords decreased, as swords forged from more uniform steel replaced them. Pattern welded inserts were also used in seaxs (large single edged knives) and spearheads
The technique of pattern welding reappeared much later as European craftsmen tried to imitate the patterns seen in watered-steel (Damascus Steel) artefacts made from a single piece of crucible steel. The technique was thus described as damascening, in reference to the steel swords and artefacts sold through Damascus. The technique is still used to this day to produce the intricate patterns of very high quality shotguns.
In Asia two traditions of forming patterned blades arose by development of the piling technique using dissimilar types of iron. In Japan, low and high carbon steel components were welded together, then forged out, folded and welded back on itself repeatedly, to form finely layered steel. On quenching this produced alternate layers of pearlite and martensite, which were revealed by etching and polishing. In Southeast Asia, a similar technique developed in Malaysia and Bali but in this case the patterns were formed due to the use of steel containing a little nickel (pamur). This could be from meteoritic iron from the Prambana meteorite (now in the Kraton Gardens, Surakarta), or smelted from nickel rich iron ore, possibly from Sulawesi, in the Celebes Isles,