Yes, it is possible to sharpen a dull katana to restore its cutting edge. Sharpening a katana involves removing material from the blade to create a new, sharp cutting edge. However, sharpening a katana is a skill-intensive process that requires expertise, knowledge, and the appropriate tools.

Here are some important points to consider when sharpening a dull katana:

1. Seek Professional Assistance: It is recommended to seek the help of an experienced swordsmith or a professional who specializes in katana sharpening. They possess the necessary skills, knowledge, and tools to properly sharpen the blade without compromising its integrity.
2. Preservation of Traditional Shape: When sharpening a katana, it is crucial to maintain the traditional shape and curvature of the blade. A skilled swordsmith will ensure that the original geometry of the katana is preserved during the sharpening process.
3. Removal of Material: Sharpening a katana involves removing material from the blade to create a new, sharp edge. This process requires careful control and precision to maintain balance and structural integrity while achieving the desired sharpness.
4. Blade Maintenance: After sharpening, it is important to properly clean and oil the katana to protect the newly sharpened edge and prevent rust or corrosion.

Due to the specialized skills and tools required, attempting to sharpen a katana without proper knowledge and experience can lead to irreversible damage to the blade. It is advisable to entrust the sharpening process to professionals who have expertise in working with Japanese swords.