Restoring Koto: Assessing Wear and Preservation Before Re-polishing

Age-related Changes in Old Sword Blades

Japanese swords that have been owned and stored over long periods of time may undergo significant changes in the visibility of the hamon and the luster and color of the jihada, depending on the storage environment and the condition of past care. In sword blades that have aged over several decades or have been passed down through multiple generations, the current state differs from blade to blade depending on when past sharpening was done and what kind of storage has taken place afterward.

The symptoms most commonly seen as age-related changes are as follows.

• Light rust and spot rust: Initial rust caused by humidity changes or depletion of oil. Corrosion will progress if left unattended
• Wiping marks: Accumulation of fine scratches that occur during maintenance
• Blade chipping: Chipping of the blade edge caused by use or improper storage
• Cloudiness of the jihada: Opacity of the jihada surface caused by oxidation or deterioration of the oil film
• Loss of clarity in the hamon: A state where the contrast with the jihada is lost and the luster of the hamon becomes dull
• Reduction from sharpening: A state where the blade has become thinner due to accumulation of past sharpening

These changes may appear individually or in combination. Multiple factors shape the current state of the blade, including the humidity of the storage location, prolonged storage while in the scabbard, and the type and condition of deterioration of the oil used.

Determining Whether Re-sharpening is Necessary

When evaluating the condition of a blade, a craftsman begins with overall observation. Since light rust and cloudiness of the jihada can sometimes be improved through proper care and careful wiping, it is not immediately determined that sharpening is necessary. Distinguishing between surface dirt and problems that cannot be resolved without sharpening is the important work at this stage.

Consideration of re-sharpening becomes necessary when the following conditions are observed.

1. Spot rust occurs in multiple locations and cannot be expected to improve through wiping
2. Blade chipping extends to multiple locations along the blade edge
3. The reflection of the hamon is barely visible and the working of the jihada is difficult to distinguish
4. Marks from past sharpening are deep and cover the ground surface

On the other hand, not all old blades require re-sharpening. Since sharpening is a process of scraping steel with a whetstone, the blade becomes slightly thinner each time. If additional sharpening is added to a blade that already shows significant reduction from sharpening, not only will the shape balance of the edge section and spine section be disrupted, but in the worst case, structural damage such as blade fracture may occur.

Aspects such as the ridge line, the position of the sections, and the balance of blade thickness gradually change through repeated sharpening, making it possible to infer to some extent the number of past sharpening sessions from the current state. Experienced craftsmen judge what stage the blade is at by carefully observing these aspects.

Main Stages of the Blade Restoration Process

Re-sharpening begins with rough sharpening, just like normal sharpening, and proceeds in stages to finishing sharpening. However, in the case of old blades, careful observation of the current condition before work is essential. Only after confirming the distribution of rust and scratches, verifying the thickness of each part of the blade, and understanding the condition of the hamon, is the specific work plan determined.

Rough sharpening begins by gradually transitioning from coarse whetstones to finer whetstones while smoothing out irregularities caused by blade chipping and rust. The amount of steel removed in this process varies depending on the condition of the blade and the desired finish, so it is carried out carefully under the principle of keeping it to the minimum necessary. With old blades, there is a need to balance minimizing reduction from sharpening while determining how much to scrape away to remove scratches.

Finishing sharpening proceeds through cosmetic processes such as edge beveling and wiping, highlighting the grain of the jihada and the characteristics of the hamon. Features such as mokume, itame, and suguha that appear in the jihada can only be observed clearly through appropriate finishing sharpening. In the case of old blades, how much fine scratches and color unevenness accumulated over many years can be corrected depends on the quality of the steel and the remaining thickness, so all conditions cannot be treated uniformly.

Judgment on Whether Re-sharpening is Advisable and Considerations from a Cultural Property Perspective

Whether to re-sharpen an old blade is an issue that should be carefully considered not only for cosmetic improvement but also from the perspective of preserving its artistic and asset value as a sword. If the blade becomes too thin through sharpening, not only the durability but also its value as an object of appreciation and evaluation may be compromised. Therefore, the idea of limiting sharpening to the minimum necessary range is widely shared among craftsmen in the field.

Furthermore, re-sharpening is an irreversible process that cannot be undone once performed. In the case of slight cloudiness or small scratches, choosing to refrain from re-sharpening and instead continuing careful maintenance while maintaining the current state can be a rational decision for keeping the blade in good condition over the long term.

If the mounting or scabbard does not match the condition of the blade, friction inside the scabbard can cause new scratches or rust. Therefore, when checking the condition of the blade, it is recommended to also check the compatibility with the exterior.

When considering re-sharpening, it is important to make decisions not only based on the immediate goal of "improving the current appearance" but also from a long-term perspective of "how to maintain it for the coming decades."

Information to Communicate When Consulting with a Craftsman

When consulting with or requesting re-sharpening from a craftsman, it is desirable to provide information about the provenance of the blade and the timing of past sharpening if such information is known. Information about when the blade was sharpened and what kind of environment it was stored in is an important clue for inferring the current state of the blade.

Even if the provenance is unknown, organizing and providing the following information will make it easier for the craftsman to grasp the condition.

• Specific locations of symptoms of concern (where rust, blade chipping, or cloudiness is located)
• Environment of the storage location (humid location, prolonged storage, condition of the scabbard, etc.)
• How much time has elapsed since the last maintenance
• The inscription or shape of the nakago attached to the blade (which can provide clues to provenance)

Since each old blade has a unique history, even if scratches appear similar, the condition of the steel beneath them can vary greatly from blade to blade. The process of carefully aligning the approach of "how much to sharpen" and "how much to leave untouched" in front of the actual blade becomes the most important exchange in re-sharpening.

Summary

Re-sharpening of old Japanese swords is not merely a cosmetic restoration process but rather a process that requires comprehensive consideration of the blade's thickness, structural integrity, and preservation of its value as a cultural property. The approach of carefully assessing the degree of reduction from past sharpening and the accumulation of past maintenance, and applying sharpening only within the necessary range, is cherished as a fundamental attitude for transmitting the blade to future generations.

For determining the condition of a blade and whether sharpening is appropriate, expert judgment based on examination of the actual object is essential. When searching for swords online, we recommend carefully reviewing the sharpening history and preservation condition information listed on the listing page, and submitting any questions through the contact form.