Sharpened katanas, samurai swords

During the Edo period, the quality of a sword could be displayed in a macabre way. Some blades were given a saidan-mei on the tang, often inlaid with gold, noting the date and type of cut made by an official expert, sometimes the number of bodies pierced with a single blow. The Yamano family, testers for the shogun, left many signatures of this type. Blades by Kotetsu and other illustrious swordsmiths still bear these inscriptions, which have become both certificates of effectiveness and arguments of prestige for the owner. The practice, linked to places of execution, used convicts or corpses, with codified cuts from the knee to the shoulder. Today, these inscriptions can still be seen in collections and museums, a chilling reminder of the link between technique, judicial ritual, and martial reputation.

In the art of cutting, the real "strength" isn't muscular, it's geometric. Visit hasujiThe alignment of the wire with the trajectory decides whether the blade splits or tears. A slight component of slice (pulling or pushing on the contact) lengthens the cut and reduces resistance. The most effective zone remains the monouchithe last third of the blade; the tenouchi temporizes the closing of the hands to freeze the angle at the precise moment of impact. Useful speed comes from a relaxed body that organizes itself, not from a tense arm. On the technical side, the niku (domed) prevents the blade from "sticking", and traditional polishing aligns the planes and wire; beyond a certain threshold, more sharpening won't save a badly held angle. Already popularized in the Edo period (XVIIᵉ century) by the tameshigiriThis principle remains the key today... cutting clean means cutting straight.

The katana 's famous curvature is not just a matter of style: it's the result of engineering that's as elegant as it is effective. During forging, the master smith applies a thinner layer of clay to the cutting edge than to the back of the blade. During tempering, the cutting edge cools faster, creating a harder structure (martensite), while the back remains softer. This thermal shock causes internal tension... and gives rise to the sword's natural curvature. The result is a perfect balance between cutting power, strength and flexibility.
The katana thus becomes a living weapon, born of fire and intelligence, as deadly as it is harmonious.