The science
The blade of a sword needs to be hard edged to retain its cutting sharpness and withstand direct blows. Yet to enable the sword to release its energy once it has been halted by an impact, it also needs to be flexible. If the steel is too hard, it will be brittle and will snap, but if it is too soft, it will buckle and not hold its edge. This dilemma has plagued weapon makers from the earliest days.
By the early Saxon period, sword makers were trying to overcome the inherent shortcomings of working with metals of unreliable quality. The answer to creating a tough yet flexible blade was in the laminating of iron and steel. Iron is relatively soft and flexible, whereas the higher carbon content in steel makes it harder and more rigid.
Pattern welding
To combine the benefits of both metals, strips of each would be sandwiched into a laminated bar. After repeated hammering under heat, the layers were welded together. The bar was then twisted and hammered flat once again. To this basic core, hard steel cutting surfaces were hammer-welded along the edges.
After the final shaping and cleaning of the sword, a process called acid etching (which removes a microscopic surface layer of the metal) would reveal an intricate pattern of swirls and bands running the length of the blade – evidence of the twisted and bound layers of the two component metals. These patterns gave the style of welding its name: pattern welding.
Mass production
By the time of the Norman invasion of 1066, steel production had become much more accomplished and reliable, with heating and cold-plunge tempering becoming a well-practised method of hardening steel. This resulted in a wider mass production of swords.
Tests conducted by Mike Loades at the Royal Military College of Science Testing Ground at Shrivenham proved that, although swords changed in design over the years, from Saxon 'fuller' grooved blades designed for lightness and strength to the diamond profile of the late medieval long sword, the principles of hardness, strength and flexibility remained the basis for all types.
