Cleaning a katana with alcohol is generally not recommended. While alcohol can be used for cleaning some types of blades or removing certain substances, it is not suitable for cleaning a traditional Japanese katana. Here's why:

1. Potential Damage to the Finish: Alcohol can potentially damage the lacquer finish or polish on the blade. Traditional Japanese katana blades often have a delicate surface treatment, and alcohol may cause discoloration, fading, or other adverse effects.
2. Drying Effect: Alcohol has a drying effect, which can remove natural oils or protective coatings from the blade. This can leave the metal more susceptible to rust or corrosion.
3. Solvent Effect: Alcohol can act as a solvent and may remove or damage any oils or lubricants that have been applied to the blade for protection or preservation.

When cleaning a katana, it is generally recommended to use non-abrasive and non-reactive materials, such as soft cloths or specialized cleaning tools designed for swords. If necessary, a mild soap solution with water can be used to gently clean the blade, followed by careful drying and application of appropriate sword maintenance oils.

If you have specific concerns about cleaning your katana or wish to ensure proper maintenance, it is advisable to consult a professional swordsmith or an experienced practitioner who can provide guidance and assistance based on their expertise.