What is a “Hamon”

A hamon in W2 tool steel.

A hamon is an ancient Japanese bladesmith technique. The process produces usually a line created during the heat treatment process. It showcases the difference between the hardened edge, the soft spine. It is also a sign of a skillful smith. However this line isn’t easily seen unless polished thoroughly and lightly etched. It is believed to be a visual representation of the blades “soul”.

Apparently “hamon” also has to do with an anime show. (I don’t know much about the show). That is not what is being referenced here