Sorry, my view is completely different. I don't know what sort of sword John has shown but it looks Indo-Persian. When it's a good sword there can be hidden wootz under the patina, I personally would call it corrosion.
There are people who would pay a lot of money to receive a polished and etched blade. It takes a lot of time and energy to bring a blade back to life. I personally would clean such a blade! Just my opinion!
I also clean in most cases brass, copper and silver, it soon becomes dull again.