This term is sometimes used in regards to Japanese swords and when used in this context it will refer to a blade being folded with more than one type of steel.
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.
The steel used to make a Japanese sword may be folded. Traditionally this was done to aid in purifying the steel, but the availability of pure modern steels makes this step unnecessary for achieving excellent results. This technique may be used on replica Japanese blades with the intent to construct them according to more traditional methods and to impart a traditional visual aesthetic to the blade. More than one different type of steel may be melded and folded together to create a blade with composite properties from several types of steel, but it is also common for a single steel to simply be folded on itself.
The fuchi is a metal hilt collar between the tsuka and the tsuba.
The habaki is a metal collar (usually of brass) mounted at the base of the blade above the tsuba guard and is used to keep the sword from falling out of the saya and to support the fittings below.
The kashira is a butt cap (or pommel) on the end of the tsuka.
The component which is the mouth of the scabbard of a Japanese sword. On traditional swords and better replicas it is traditionally made of buffalo horn and its purpose it to prevent the wood scabbard from splitting at its opening from repeated contact and impact.
The kojiri is the tip cap for the saya scabbard of a katana. Traditionally made with buffalo horn and better replicas will also be made of horn.
A knob on the side of the scabbard used as the attachment point on which to attach or knot a sageo cord.
This construction method was common to traditional katanas but is rarely utilized in replicas due to the complexity involved. A laminated blade will be a composite of several different steels and these are used to create different sectional partitions of the blade. There are several different lamination types of varying complexity; some are simpler and involve a softer core of steel being pointed into a harder steel ‘’jacket’’ whereas others can utilize as many as seven or more different partitions of steel of varying qualities. The individual partitions of the blade may be folded before being used as a component for the overall blade composite depending on preference. Once constructed the sword can then be differentially-hardened when tempering.
The mekugi is a small bamboo peg for securing the tsuka (grip) to the nakago (tang). Most Japanese swords have two for extra security, though a single peg was common historically.
The menuki are metal ornaments placed on the rayskin of the grip. They are overlaid with the cord grip and partially covered to keep them into place when the grip is completed with a grip wrap.
The tang of the blade inserted into the handle. Traditionally the swordsmith would leave his signature on this part of the blade. Some modern replicas will leave some manufacturer signature or identifying info on this part of the blade.
The sageo is the cord used to tie saya to the belt/obi when worn. It is attached to the scabbard, often with an elaborate decorative knot.
The ray or shark skin wrapping of the wooden handle. Most replicas will have inlaid panels of these and very high quality replicas will have the grip wrapped entirely over in rayskin.
The saya is a wooden scabbard for the blade; traditionally finished in lacquered wood.
The seppa are metal washers above and below the tsuba used to tighten the fittings. These are usually made of brass.
A style of katana hilt mounting. Unlike most katana with elaborate cord wrapping a katana mounted “Shirasaya” style has the blade mounted into very plain wood with a plain wood scabbard to match. Traditionally this was a way to preserve sword blades that were not going to be used for a substantial length of time. Lack of cord and other fittings prevented accumulation of moisture to better preserve a blade for longer term storage. The blade was often pinned to the wooden grip to ensure that it was still functional in an emergency.
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.
The tsuba is the hand guard of a Japanese bladed weapon.
The cord wrap which is braided and knotted to a katana tsuka handle. Cotton, Silk and Leather are common. Materials such as jute-like twine or even elaborately folded and lacquered paper were also used historically.