What is Kagami Hada in Japanese Katana terminology?

Kagami Hada or 鏡肌 in Japanese, refers to a state where the ground iron (jigane) of a Japanese sword is forged so finely that the grain is not easily discernible to the naked eye. This is often seen in swords made during the Shinshintō period (new new sword period, 1781-1876).

The term ""Kagami Hada"" literally translates to ""mirror skin/grain"", which describes the smooth and almost mirror-like surface of the sword. This is achieved by forging the ground iron (jigane) very finely and evenly, to the point where the grain is not easily visible.

This pattern is also referred to as ""Mujihada"" (無地肌), which translates to ""plain skin/grain"". This term is used to describe the state where the grain is so finely packed that it appears almost plain or without pattern.

The quality of the ground iron (jigane) and its pattern (hada) play a significant role in the aesthetics and value of a Japanese sword. It is one of the factors that sword connoisseurs look at when evaluating a sword. The Kagami Hada, with its smooth and almost mirror-like surface, is a distinctive feature that sets the sword apart.