For other uses of the word blade, see Blade (disambiguation)

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A blade is the part of a sword that is used to cut (as opposed to the hilt). Sword blades are generally made out of the toughest metal available. In antiquity, this was copper, then bronze. Once iron was discovered, it was used and finally steel. Prior to the invention of steel, several techniques were developed for reducing the brittleness of iron. Perhaps the most well known is pattern welding techniques such as those used for samurai swords or 'damascus' blades. This was a very labor-intensive technique - and so such swords were very expensive.

Various techniques were also employed to make the blade harder. Copper and bronze can be "work-hardened" by simply hitting the blade with a hammer while it's cold. Blades made of steel with a high enough carbon content (greater than 0.2%) could be heat-treated by heating the steel up to a critical point (most alloys become non-magnetic at that point), then quenching it in water. Quenching puts an enormous amount of strain on the metal, and oftentimes a sword would break into pieces during that step. If the sword survived heat-treating, it would be tempered by heating it to a relatively low temperature for an extended period of time. The tempering process would make it slightly softer, but also tougher and "springier," and thus less likely to break or chip during the rigors of combat.

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 awhile, 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.

Decoration was often applied to the blade - usually engraving and sometimes inlaying with gold. In the 19th century, it became common to etch designs on the blade using acid and a wax template.

Swords may have either a straight blade or a curved one. A straight sword was primarily intended for stabbing, whilst a curved sword was intended for slashing.

Stab wounds were more lethal, and so straight swords were generally preferred, at least by infantry.

For a horseman, stabbing was not practical because it is hard to make a horse move swiftly backward should the thrust fail to strike the victim. The cavalryman would then be at the mercy of his erstwhile victim. This was not so important in massed cavalry charges, in any case in such attacks the cavalry would often be in closely packed formations in which slashing would not be possible. Consequently, European heavy cavalry generally had straight swords.

Cavalry that engaged in single combat or in looser formations normally had curved swords. In order to cut, a sword had to be drawn across the victim's skin, and a curved sword was more suitable for this. The blade was only sharpened on the outer edge and the radius of curvature was equal to the distance from the centre about which the blade was rotated - i.e. the distance from the blade to the shoulder.

In European swords, this was usually a full arm's length, but in the Middle East and Indian swords it as generally a much shorted distance - typically 50 cm or so. This gave Eastern cavalry a great advantage over their European counterparts because they were able to fight at a closer distance than the Europeans were used to and therefore get inside their sword arc.

Single-edged swords have a back. This is the unsharpened edge. Early 19th century swords had a "pipe-backed" appearance, whereby they had a thickened ridge along the back to make the blade stronger.

As the 19th century progressed and metallurgy improved, pipe backs were no longer necessary. They gave way to grooves forged in the side of the sword and these were known as "fullers". Fullers were made by positioning a blade over a bottom fuller, setting a like sized top fuller on the top side of the sword, and hitting the top fuller with a hammer. The metal had to be hot to do this. What happened was that the fibers of the metal would spread. As well as making the sword lighter, they made it more flexible and less likely to snap.