Editing Blade (section)

===Materials===
Typically blades are made from a material that is about as [[hardness|hard]], though usually harder, than the material to be cut. Insufficiently hard blades will be unable to cut a material or will wear away quickly as hardness is related to a material's ability to resist [[abrasion (mechanical)|abrasion]]. However, blades must also be [[toughness|tough]] enough to resist the dynamic load of impact and as a general rule the harder a blade the less tough (the more brittle) a material. For example, a steel axehead is much harder than the wood it is intended to cut and is sufficiently tough to resist the impact resulting when swung against a tree while a ceramic kitchen knife, harder than steel, is very brittle (has low toughness) and can easily shatter if dropped onto the floor or twisted while inside the food it is cutting or carelessly stored under other kitchen utensils. This creates a tension between the intended use of the blade, the material it is to be made from, and any manufacturing processes (such as [[heat treatment]] in the case of [[steel]] blades that will affect a blade's hardness and toughness). A balance must be found between the sharpness and how well it can last. Methods that can circumvent this include [[differential hardening]]. This method yields an edge that can hold its sharpness as well as a body that is tough.<ref name="thearma.org; edge damage">{{cite web|url=http://www.thearma.org/essays/damagededge.htm|title=Edge Damage on Swords|website=www.thearma.org|access-date=20 March 2018}}</ref>

====Non-metals====
{{See also|Blade (archaeology)}}
Prehistorically, and in less technologically advanced cultures even into modern times, tool and weapon blades have been made from wood, bone, and stone.<ref>{{cite journal|last1=Driscoll|first1=Killian|last2=García-Rojas|first2=Maite|title=Their lips are sealed: identifying hard stone, soft stone, and antler hammer direct percussion in Palaeolithic prismatic blade production|journal=Journal of Archaeological Science|date=July 2014|volume=47|pages=134–141|doi=10.1016/j.jas.2014.04.008|url=http://lithicsireland.ie/driscoll_garcia_rojas_2014_identifying_palaeolithic_blade_production_journal_archaeological_science_47.pdf|access-date=19 July 2017}}</ref> Most woods are exceptionally poor at holding edges and bone and stone suffer from brittleness making them suffer from fracture when striking or struck. In modern times stone, in the form of obsidian, is used in some medical scalpels as it is capable of being formed into an exceedingly fine edge. [[Ceramic knife|Ceramic knives]] are non-metallic and non-magnetic. As non-metals do not corrode they remain rust and corrosion free but they suffer from similar faults as stone and bone, being rather brittle and almost entirely inflexible. They are harder than metal knives and so more difficult to sharpen, and some ceramic knives may be as hard or harder than some sharpening stones. For example, [[Sapphire#Synthetic sapphire|synthetic sapphire]] is harder than natural sharpening stones and is as hard as alumina sharpening stones. [[Zirconium dioxide]] is also harder than garnet sharpening stones and is nearly as hard as alumina. Both require diamond stones or silicon carbide stones to sharpen and care has to be taken to avoid chipping the blade. As such ceramic knives are seldom used outside of a kitchen and they are still quite uncommon. Plastic knives are difficult to make sharp and poorly retain an edge. They are largely used as low cost, disposable utensils or as children's utensils or in environments such as air travel where metal blades are prohibited. They are often serrated to compensate for their general lack of sharpness but, as evidenced by the fact they can cut food, they are still capable of inflicting injury. Plastic blades of designs other than disposable cutlery are prohibited or restricted in some jurisdictions as they are undetectable by metal detectors.

====Metals====

{{see also|Metallurgy#History}}

Native [[copper]] was used to make blades by ancient civilizations due to its availability. Copper's comparative softness causes it to deform easily; it does not hold an edge well and is poorly suited for working stone. [[Bronze]] is superior in this regard, and was taken up by [[Bronze Age|later]] civilizations. Both bronze and copper can be [[work hardening|work hardened]] by hitting the metal with a hammer. With technological advancement in smelting, [[Iron Age|iron]] came to be used in the manufacturing of blades. [[Steel]], a range of alloys made from iron, has become the metal of choice for the modern age.

Various alloys of steel can be made which offer a wide range of physical and chemical properties desirable for blades. For example, surgical scalpels are often made of stainless steel so that they remain free of rust and largely chemically inert; tool steels are hard and impact resistant (and often expensive as retaining toughness and hardness requires expensive alloying materials, and, being hard, they are difficult to make into their finished shape) and some are designed to resist changes to their physical properties at high temperatures. Steels can be further heat treated to optimize their toughness, which is important for impact blades, or their hardness, which allows them to retain an edge well with use (although harder metals require more effort to sharpen).

====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]].