Caring for Your Japanese Sword — Proper Maintenance to Preserve a Masterpiece

Why Regular Maintenance of Japanese Swords is Essential

Japanese katana are precision iron products forged from carbon steel. When proper maintenance is neglected, moisture and oxygen in the air react to cause oxidative corrosion (rust), and within just a few months the beauty of the hamon and jihada is lost. Even swords designated as National Treasures or Important Cultural Properties have retained their brilliance to this day only through the careful, continuous maintenance carried out by successive keepers. To keep a good sword in use for a long time and pass it down to the next generation, regular and accurate maintenance is absolutely essential.

Tools Required for Maintenance and Where to Purchase Them

Proper maintenance requires specialized tools. Understanding the role of each tool helps prevent damage from incorrect maintenance.

Tool sets are available at the Swords and Armor Museum Shop (Sumida Ward, Tokyo) and various sword specialty shops throughout Japan, as well as through mail order authorized by the NBTHK. You can also find beginner-level complete sets online by searching for "Japanese sword maintenance set." Since quality varies widely, it is recommended to choose tools sold by specialized sword shops whenever possible.

Correct Maintenance Procedure (Step-by-Step)

Before beginning, secure a stable, spacious work surface and use a sword stand or folded towel to prevent the sword from rolling off. Always wear white gloves.

Step 1: Remove the mekugi and detach the tsuka Gently tap the mekugi from outside the tsuka using the mekugi puller to extract it. Lightly grasp the tsuka with your right hand and slowly pull the entire tsuka away to expose the blade.

Step 2: Wipe away old oil Using dry wiping paper, carefully remove the oil remaining on the blade from the previous maintenance. Always wipe from the spine (munegawa) toward the edge (hagawa). Wiping in the opposite direction risks cutting your hand on the edge and can also cause scratches.

Step 3: Apply uchiko Gently dab uchiko onto the blade to absorb the oils. Never rub forcefully. Since uchiko contains abrasive material, applying too much pressure will create fine scratches on the jihada surface and damage the finish.

Step 4: Wipe away the uchiko Completely wipe away the uchiko using fresh wiping paper. Again, wipe from spine to edge.

Step 5: Apply choji oil thinly Place a few drops of choji oil on the edge of the wiping paper and spread it extremely thinly and uniformly over the entire blade. If too much oil is applied, it will attract dust and cause rust instead; after application, lightly wipe with another sheet of paper to confirm a thin film state.

Step 6: Reattach the tsuka and insert the mekugi Slide the blade back into the tsuka and insert the mekugi to secure it. Gently pull to confirm the mekugi is firmly in place.

Seasonal Maintenance Calendar

Japan's climate undergoes significant seasonal temperature and humidity fluctuations, so maintenance frequency and precautions vary by season.

Spring (March–May) — Responding to Pollen and Warming

• Frequency: Once per month is the standard
• Spring is when humidity begins to rise. Pollen and fine airborne particles easily adhere to the blade, so perform careful cleaning with wiping paper. This is also a good time to check that oils have not deteriorated over winter.

Rainy Season to Summer (June–August) — Most Critical Season

• Frequency: Twice or more per month recommended
• Japan's rainy season and summer can experience relative humidity exceeding 80%, making this the season when rust progresses most rapidly. Constantly monitor the humidity of the storage location and, if necessary, use desiccants such as Dry Pet (placed so they do not touch the sword directly). Temperature differences between air-conditioned rooms and the storage location can cause condensation. When removing the sword from an air-conditioned room, allow it time to acclimate to the temperature before handling.

Autumn (September–November) — Inspection and Adjustment Season

• Frequency: Once per month
• The first maintenance after the high humidity of summer should be thorough. Check carefully for signs of fine rust (darkening, early signs of white rust). Also inspect the condition of the shirasaya and sword bag, checking for mold or signs of moisture.

Winter (December–February) — Dryness Countermeasures

• Frequency: Once per month; check every two weeks
• In winter's low-humidity environment, choji oil tends to dry and evaporate. Apply slightly more oil and establish a habit of checking every two weeks to ensure the oil film is maintained. Avoid storing the sword near heating appliances, as they cause rapid drying.

Storage Environment and Storage Considerations

After maintenance is complete, carefully place the blade in a shirasaya. The shirasaya is an unvarnished wooden storage scabbard; the wood absorbs and releases moisture appropriately, helping stabilize the blade environment.

Ideal storage conditions are temperature 15–25°C, humidity 40–60%, with complete avoidance of direct sunlight. The middle shelf of a closet, a dedicated sword box (toubako), or a paulownia wood box are suitable. When storing horizontally, position the blade edge upward to minimize movement of the blade inside the scabbard. Volatile components in mothballs (such as naphthalene) harm metal and lacquer, so avoid using them inside sword boxes.

Establish a habit of removing and inspecting the sword at least once every three months to check for new rust or moisture inside the scabbard.

Requesting Work from a Togishi and Restoration

With continued maintenance, accumulated uchiko polishing gradually thins the blade. When rust progresses or scratches develop, individual efforts reach their limits. In such cases, consulting a professional togishi (sword polisher) is best.

A togishi is not merely someone who sharpens blades with whetstones; they are artists who bring out the original hamon and jihada beauty of the sword. Re-polishing often revives a once-dull hamon to brilliant clarity and restores the luster of the jihada's surface. Choose a togishi carefully and prioritize recommendations from trusted sword merchants or sword preservation organizations. Polishing fees vary depending on the blade length and condition, but should be viewed as a necessary investment in maintaining your sword's value.

Common Mistakes and Precautions

• Applying uchiko too forcefully → Creates fine scratches in the jihada. A gentle dabbing motion is sufficient
• Applying too much choji oil → Attracts dust and paradoxically causes rust; the principle is extremely thin and uniform application
• Bare-handed contact with the blade → Skin oils from fingers are a strong rust promoter; always wear white gloves
• Metal tool contact with the blade → Tweezers and similar tools cause fine scratches
• Incorrect wiping direction → Wiping from edge to spine risks cutting your hand and causes scratches

If you are uncertain about maintenance, attending demonstration workshops held by sword museums or sword preservation organizations can also be beneficial. Through consistent proper maintenance, the sword you hold will continue to shine for centuries to come and be passed down to future generations.