Hi Franco,
Thank you for insight into my sword. I'm going to have the sword looked into by someone affiliated with Japanese swords. I understand that you may believe the discoloration might be heat related. I'm no expert by any means but I will look into it. Based upon it not being heat altered what type of value do you believe it has? If it has a substantial value I would consider having it professional polished. Thanks again for your insight.
all the best,
Tom