Faq Categories: Japanese Blade Tempering / Hardening Terms

In contrast to Through-Tempered, this is the traditional method for tempering the Japanese sword. Before quenching the blade the swordsmith will coat it with clay and the varying thickness of the clay will determine how quickly the blade will cool when quenching. The thin layer along the edge will flash cool the edge and the thicker clay on the body and spine will slow its cooling. This results in the blade having two separate levels of hardness; the edge will be harder steel which will better hold a sharp edge and the body will be softer and have some shock-absorbing properties. In addition to this the polishing of the blade will reveal a wave-like hamon line that denotes the border between the differentially-hardened regions of the blade. 

While this traditional method does make a blade with a fine and hard edge the drawbacks are that this edge is more brittle than a softer through-hardened edge and make it more likely to chip or take damage when struck against a hard or dense target. The softer spine of the blade also has a tendency to take a bend if a poor cut is made against a target, requiring it to be straightened again by a professional.

This is similar to most other types of swords which are made from a single piece of steel with a uniform HRc hardness. Though not the traditional method, this type of blade composition can be spring-tempered so that it can flex and return to straight which makes it less likely to be damaged or become asymmetric if the user executes a poorly aligned cut on a target. It is also easier to polish out scuffs and scratches on these blades which do not have a hamon. Altogether this makes this blade type suitable for beginners or tameshigiri enthusiasts who wish to do substantial amounts of test cutting and minimize the level of maintenance their blade will need.