Editing Blade (section)

====Combined materials and heat-treatments====
It is possible to combine different materials, or different heat treatments, to produce desirable qualities in a blade. For example, the finest Japanese swords were routinely made of up to seven sections of metals and even poorer quality swords were often made of two. These would include soft irons that could absorb the energy of impact without fracturing but which would bend and poorly retain an edge, and hard steels more liable to shatter on impact but which retained an edge well. The combination provided a sword that would resist impact while remaining sharp, even though the edge could chip if abused. [[Pattern welding]] involved [[forging]] together twisted bars of soft (bendable) low carbon and hard (brittle) higher carbon iron.<ref>{{cite journal | last = Maryon | first = Herbert | author-link = Herbert Maryon | date = 1948 | title = A Sword of the Nydam Type from Ely Fields Farm, near Ely | journal = Proceedings of the Cambridge Antiquarian Society | volume = XLI | pages = 73–76 | doi = 10.5284/1034398 }}</ref> This was done because furnaces of the time were typically able to produce only one grade or the other, and neither was well suited for more than a very limited use blade. The ability of modern steelmakers to produce very high-quality steels of various compositions has largely relegated this technique to either historical recreations or to artistic works. Acid etching and polishing blades made of different grades of steel can be used to produce decorative or artistic effects.

Japanese sword makers developed the technique of differential hardening by covering their sword blades in different thicknesses of clay before [[quenching]]. Thinner clay allowed the heated metal to cool faster, particularly along the edge. Faster cooling resulted in a finer crystal structure, resulting in a blade with a hard edge but a more flexible body. European sword makers produced similar results using [[differential tempering]].