Pattern Welding

Pattern welding is a smithing technique in which a smith forge-welds together several rods or bars of iron and steel with differing carbon content, then folds or twists the resulting billet before hammering it out into a blade, so that the different metals form visible layered or twisting patterns on the finished surface while also combining a harder steel with a softer, tougher iron to balance edge-holding ability against resistance to breaking. The technique is attested among Celtic and Germanic smiths from the first millennium BC, and became common for both structural strength and surface decoration among Celtic smiths by the second and third centuries AD. Viking Age smiths particularly favored twisting steel bars together to produce chevron patterns in sword blades, and by the sixth and seventh centuries some smiths were overlaying patterned steel onto a softer iron core to improve a blade's flexibility, but the technique fell out of use in Europe by the end of the Viking Age as improved steelmaking made single-piece blades practical.