Blades

A blade is the flat part of a tool, weapon, or machine (such as a fan) that normally has a cutting edge and/or pointed end typically made of a flaking stone, such as flint, or metal, most recently steel. A blade is intentionally used to cut, stab, slice, throw, thrust, position and/or place (an example of this is razor wire), shoot (an example of this is the ballistic knife), scrape (an example of this is an ink eraser) or strike an animate or inanimate object.

The basic idea of a blade is very similar to a sharp point. The shape concentrates all the force onto a very small area, resulting in a high amount of pressure which allows it to penetrate matter. A serrated blade (a blade which has many small "teeth") takes this further as each individual tooth concentrates the force on a smaller area which helps cut through denser materials. A serrated knife can cut through objects solely with a sliding motion with little pushing force, this is useful for tools which require these attributes such as bread knives. Some bladed weapons (and tools) have curved blades. A curve can serve two purposes, the first is that it allows for slicing by continuing to "push" on the surface as it is drawn across it. The other effect is to allow the force to be concentrated in an even smaller area.

Case hardening is a process of increasing the carbon content at the surface of very low carbon steel. It is done by placing the object to be hardened in a sealed container along with carbon-containing material; in antiquity, this material was usually horn or hide. The container would then be heated until it was glowing red, and held at that temperature for a while, based on the size of the part being hardened, allowing carbon to penetrate the steel by a few thousandths of a centimeter. At that point, the object would be dumped out of the container into a water bath to quench it, resulting in a very hard surface, but completely unhardened core. There is very little evidence of this having ever been done to swords except, perhaps, the very earliest of iron blades. Due to the inherent weakness of a sword's cutting edge, coupled with the high-impact stresses of combat, such a thin hardened surface over a soft core would provide very little advantage in terms of edge-holding, other than mild wear resistance.

Blades dull with use and abuse. This is particularly true of acute blades and those made of soft materials. Dulling usually occurs due to contact between the blade and a harder substance such as a ceramic, stone or a tougher metal. To a first approximation, a harder material cannot be deformed by a softer material at their interface because the stress on both materials is the same at the interface and so the softer material will yield first. One exception to this is when the highest stress isn't at the contact point; this is why one can easily bend a steel paper clip even though an end of the same paper clip could scratch one's skin. Swords may have either a straight blade or a curved one. A straight sword was thought to primarily intended for hacking and stabbing, yet recent studies have shown this to be untrue, as many slicing techniques were used.