How to tell the Kizu flaws of a blade.

As it is forged repeatedly, there are cases where impurities are not completely removed or small mistakes during the forging and tempering process can cause kizu (flaws) in the sword. 
Kizu is the evidence of repeated forging, but kizu may cause problems during actual use and for authentication. Its very important to treat the kizu objectively and rationally. 

When a crack appears in the tempered edge and extends to the blade it is called hagire. These are very fatal flaws, it is considered a defeat blade and unacceptable. the blades must be scrapped if hagire happen. because these blades are very dangerous, its going to break in practical use. This type of crack comes from the hardening failure. the cracks does not only appear on the cutting edge,  sometimes appears on shinogi or mune too. the blade  if hagire happened, we even never discount sale these blades.

As for our forging experience. The most common imperfection is kitae-ware; horizontal "lines" (splits) generally due to a poor weld between layers of steel. Ware may occur anywhere on the blade (mune-ware, tate-ware, shinogi-ware, etc). Usually,  This kind of flaw is the easiest to be found,  It is not good for its visibility. But in most cases, it is not so serious as it looks like, These are very common. A small flaw from fold welding work does not make the quality of the steel down. unless it is rather large, it will generally not impede its practical use. We have to see the colour and brightness of the steel (in other words, the condition of the steel particles) to know its quality. Normally, our QC decides blades will be scrapped if kitae-ware is over 10mm; and It is considered acceptable if kitae-ware less than 5mm. (we consider discount sale blade if kitae-ware 5-10mm)

During the tempering process, due to a bad weld between layers when blade was forged, Air or carbon pockets appear in the steel. This is known as fukure in Japanese. It always happens on tamahagane steel.  Although these will not likely affect the structural integrity of the sword, the blade still will be scrapped if the hole diameter is over 1mm. it is considered acceptable if the hole diameter is less than 0.5mm. 

Nioi-gire (Partially Missing/Skipping Tempering Line), happens in a clay tempered, differentially hardened process . If the hamon (temperline) is interrupted or runs off the blade at any point, or off the boshi; it is a major, normally fatal flaw. These blades cant be used for practical cutting practice. We always offer heavy discounts for display purposes or iaido. 

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