Suna-gashi (砂流し) is a term used in the context of Japanese swords. It refers to a pattern where the ""Nie"" (沸) - the visible particles of hardened steel - appear along the cutting edge of the blade in a line, following the grain of the blade.
The term ""Suna-gashi"" translates to ""sand flow"" in English. It is named so because the pattern resembles the striped pattern created by sand flowing in a river. This feature is often seen in the works of the S?sh? school (相州系), one of the five main traditions of Japanese sword making.
Therefore, ""Suna-gashi"" adds a unique and beautiful visual effect to the blade, enhancing its overall aesthetics and value.