UBU-HA = virgin edge
 
Un-sharpened cutting edge near the tang on the new blades. It is a manner of Japanese swords.

 
On newly forged blades, polishers never make it sharp on the cutting edge near the tang. They keep the original of forging there. The length may be 10cm or so, for katana/tachi blades. 3cm - 5cm for tanto blades. The length and the thickness is not settled exactly. It depends with each smith and polisher.
We call this un-sharpened edge "UBUHA", it means virgin edge or innocent edge. Of course the upper part is very sharpened.
 
The virgin edge becomes shorter and thinner naturally during many times polishing. Finally it disappears, and the cutting edge becomes sharp completely on entire length.
Sometimes we can see an old blade that still has a virgin edge. It is a proof of very healthy blade. We appreciate it, but we never make it again to grind a sharp edge dull. It must be kept the original of smith's work.
 
Virgin edge on Katana blade

 
Virgin edge on Tanto blade

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