How should I care for a carbon steel katana to prevent rust?
Updated Mar 2026
Carbon steel requires consistent but simple maintenance to prevent oxidation. After handling, fingerprints deposit oils and acids that can cause surface rust within days, so wiping the blade with a soft, lint-free cloth after every session is essential. Every few months - or more frequently in humid climates - apply a thin, even coat of choji oil or a modern acid-free sword oil along the entire blade surface, including near the hamon. Use a rice paper square or a dedicated uchiko ball to remove old oil before reapplying. Store the sword in its saya on a horizontal stand, away from moisture and temperature swings. Avoid storing it in a sealed case without ventilation, as trapped humidity accelerates rust far more than ambient air.