How is the purple finish applied to a ninjato blade?
Updated Feb 2026
The purple finish on a ninjato blade is applied as a surface treatment to the steel after the blade's core construction - forging, grinding, and heat treatment - is fully complete. This means the underlying blade steel and its hardness properties are established before the color treatment is applied, and the purple finish does not affect the blade's construction quality or structural integrity. Purple blade colorings can be produced through heat-based oxidation, where the blade is brought to a specific temperature that causes oxide compounds to form on the steel surface in the purple color range, or through chemical coating processes that apply a stable colored layer to the polished blade surface. The color treatment is stable for display purposes when properly cared for: avoiding abrasion and harsh chemicals, and handling with a soft cloth rather than bare hands. With proper care, the purple finish will maintain its color and vibrancy for many years of display use. Oil maintenance for the underlying steel is the same routine as for any high-carbon steel blade.