How is the blue color on the blade achieved, and will it fade?

 Updated Mar 2026

The blue finish on these ninjato blades is produced through a controlled oxidation or chemical bluing process applied directly to the polished manganese steel surface. During bluing, the steel is exposed to a hot alkaline solution or oxidizing agent that converts the outermost iron layer into a thin magnetite (Fe3O4) coating. This layer is inherently stable and does not flake or peel under normal conditions. The finish will gradually fade or shift toward gray if the blade is left unprotected in humid environments or handled with bare hands repeatedly, as skin oils introduce contaminants. Applying a light coat of camellia oil every three to four months preserves the blue tone and protects the underlying steel from moisture. Store the sword in its saya and avoid prolonged exposure to direct sunlight, which can bleach the surface over time.

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