Daily Maintenance and Long-Term Preservation of Japanese Swords — A Practical Manual for Oil, Polishing Powder, and Storage

There is a saying in the sword world that a Japanese sword is a living being. Despite being a blade made of iron and carbon, it reacts sensitively to temperature, humidity, oil, and minute vibrations, and can develop rust or scabbard bite if the storage environment changes even slightly. Maintaining a sword properly is also a responsibility to pass on to the next generation a work that a master craftsman has breathed life into. This article explains concrete methods that collectors can practice, from daily maintenance procedures to long-term storage practices.

Daily Maintenance Basics—The Role of Oil, Uchiko Powder, and Cleaning Cloth

The tools used for Japanese sword maintenance can be reduced to three.

• Choji oil (chōji-abura): A thin anti-rust oil made by mixing clove essential oil into white mineral oil, which cuts off contact with moisture in the air by applying it thinly and evenly to the blade. Applying too much will seep into the inside of the scabbard and cause the wood to deteriorate, so the appropriate amount is to spread it thinly with the pad of your finger and then lightly smooth it once more with cleaning paper.
• Uchiko (uchiko): Whetstone powder packed in a silk pouch, used to remove old oil previously applied from the blade. By lightly tapping the uchiko to attach powder to the blade and wiping it away vertically (from the spine to the edge side) with cleaning paper, both old oils and fine oxide films can be removed together. Since uchiko also has the character of an abrasive, rubbing vigorously in a horizontal direction risks damaging the boundary line of the hamon (edge border). It is important to always wipe in a consistent direction toward the tip.
• Cleaning paper (nuguigami) or cleaning cloth: Soft finishing paper or cloth used to smoothly spread choji oil or wipe away old oils and oxide films lifted by uchiko.

Regarding maintenance frequency, considering Japan's warm and humid climate, many collectors use the following as a guideline.

However, there are individual differences, and if the storage environment is a sealed paulownia box with a desiccant, there are cases where once every six months is acceptable in winter.

Managing Inside the Scabbard—The Relationship Between Habaki, Koiguchi, and Scabbard Material

When storing a sword in its scabbard, the relationship between habaki (fuchi) and koiguchi (scabbard mouth) is often overlooked. The habaki is a metal fitting that connects the blade to the scabbard, and by adhering to the koiguchi, it keeps the sword from shifting inside the scabbard. When this adhesive force weakens, "scabbard rattle" occurs, and the blade may vibrate slightly inside the scabbard, potentially damaging the hamon.

As the interior of the scabbard dries, the wood contracts and the koiguchi may loosen. Conversely, if there is too much moisture, the wood expands and "scabbard sticking" occurs, making it impossible to remove. If either is left unattended, it will adversely affect the blade, so it is important to develop the habit of regularly checking how well the koiguchi adheres.

Additionally, the scabbard of koshirae (lacquered scabbard) often has silk or other backing material glued inside, and when a sword is placed in a new lacquered scabbard, volatile compounds may be released from the backing material, potentially causing rust. When placing a sword in new koshirae, it is recommended to consult with a specialist beforehand or to store it in a shirasaya and observe the condition.

Shirasaya (white scabbard) is a scabbard made of magnolia wood dedicated to storage, and its wood surface gently absorbs and releases moisture, making it suitable for long-term preservation. If you plan to keep a collection long-term, it is ideal to prepare a shirasaya separately from the koshirae.

Designing the Storage Environment—Temperature, Humidity, Light, and Vibration

The most important factor in long-term preservation of Japanese swords is humidity control. When relative humidity exceeds 60%, a water film is more likely to form on the metal surface, and the risk of rust increases sharply. The recommended storage environment is 15–20°C temperature and 40–55% relative humidity, and the basic storage method is using a paulownia box that can stably maintain these conditions with a desiccant (such as silica gel) inside.

Paulownia has excellent insulation and moisture absorption/release properties, and it has the characteristic of mitigating sudden temperature and humidity changes in the outside air. For this reason, it has been used since ancient times for storing swords and art objects. However, paulownia boxes alone are often insufficient, and if the environment outside the box is extremely humid, it is important not to neglect changing the desiccant before storage. Since the moisture-absorbing capacity of desiccants is depleted over time, it is good to develop the habit of always checking and replacing them around the time the rainy season ends.

Exposure to light cannot be ignored either. Direct sunlight and ultraviolet rays from fluorescent lights can discolor and deteriorate the scabbard's lacquer and grip wrapping. Even when displaying, using a glass case with UV-blocking film and ensuring the sword is not constantly exposed to lighting is necessary.

Vibration is an often-overlooked risk. If a sword is placed in a room with construction work next door, on a shelf facing a busy street, or where washing machine vibrations are transmitted, the blade will continue to shift slightly inside the scabbard, potentially causing fine scratches on the hamon over time. It is preferable to store it on a wall-mounted shelf rather than on the floor, and even on a shelf, to store it horizontally on a soft mat.

When displaying on a sword stand (katana-kake), it is important to note that the correct orientation differs depending on the sword type.

• Uchigatana, wakizashi, and tanto: Storing with the edge facing upward ('ha-jō') is considered more suitable for long-term storage as an oil film is more likely to remain on the tip.
• Tachi: It is correct to display with the edge facing downward ('ha-ge'), following the direction it would be worn.

Managing Swords Not Used for Long Periods

If there is a possibility of not maintaining a sword for over a year, normal choji oil application alone may be insufficient. Sword specialists sometimes perform long-term storage treatment by thinly coating with Vaseline or industrial-grade neutral grease, wrapping it in Japanese paper, and storing it in a shirasaya. This is based on the idea of reducing oil evaporation while also having the Japanese paper act as a buffer against sudden changes in external air.

However, when removing from long-term storage, always completely remove old oil with uchiko, confirm the condition of the entire blade, and return to normal storage. If oil evaporation and oxidation have progressed over a long period, it is also important to consider consulting with a professional polisher.

For those staying abroad for extended periods or when swords are placed in storage with unknown environmental conditions due to inheritance or other reasons, temporarily depositing the sword in a Japanese sword-specialized art storage facility is also an option. Professional facilities with controlled temperature and humidity can maintain significantly more stable conditions than individual storage.

Troubleshooting—Common Problems and Initial Response

• If a thin layer of rust appears: If caught early, it may be resolved with uchiko and choji oil maintenance, but if red rust (ferric oxide) is appearing in spots, one should not attempt self-treatment but rather consult a professional polisher. While polishing is expensive and time-consuming, leaving it unattended risks the rust progressing internally and the hamon disappearing.
• Loose mekugi (peg): When bamboo or copper mekugi loosen, the blade and handle may shift when removed from the scabbard, creating a dangerous situation. Moistening the mekugi hole with a small amount of water can sometimes cause the bamboo to expand and stop the loosening, but if loosening occurs frequently, it is safer to request a professional to replace it with a new one.
• Koiguchi sticking: If moisture causes the wood to expand and the scabbard cannot be removed, one should never attempt to pull it out by force. It is strongly recommended to lightly tap the kashira (pommel) to impart vibration or to consult with a sword specialist. If forced out, there is a risk of bending stress on the blade causing breakage.

Conclusion

Daily maintenance of Japanese swords is work that anyone can practice by following three points: appropriate frequency, procedure, and tools. By gathering the three essential tools—oil, uchiko powder, and cleaning paper—and being mindful of maintenance frequency according to the season, and by regularly checking the relationship with the scabbard and paying attention to temperature, humidity, light, and vibration in the storage environment, swords can maintain their beauty for decades or even centuries.

TOUKENZA's online catalog features Japanese swords in various conditions and price ranges. If you have any questions about specific storage methods after purchase, please feel free to contact us through the inquiry form.