The vibrant crimson finish on these Nichirin replicas is achieved through a multi-step surface treatment rather than simple paint. Craftsmen first polish the 1045 carbon steel blade to a smooth, uniform surface, then apply a specialized acid-based coloring solution that chemically bonds with the steel. This process is repeated in layers, with intermediate buffing between coats, until the desired depth of red is reached. Because the color is bonded at the molecular level rather than sitting on top as a film, it resists flaking and peeling far better than painted finishes. To preserve the color over time, a light application of sword oil every few months is recommended, and the blade should be kept away from prolonged direct sunlight, which can gradually fade any surface treatment.
