Black chrome plating.
If appearance and lifespan are a primary concern and cost is secondary.
Here is an example https://www.arlingtonplating.com/capabilities/black-chrome-plating/
At the machine shop where I am employed we make bass guitar components that terminate the strings from stainless steel, some are black oxided after machining for appearance only, this is also a durable finish process, not nearly as durable as black chrome however but far less expensive.
Choose wisely.
If appearance and lifespan are a primary concern and cost is secondary.
Here is an example https://www.arlingtonplating.com/capabilities/black-chrome-plating/
At the machine shop where I am employed we make bass guitar components that terminate the strings from stainless steel, some are black oxided after machining for appearance only, this is also a durable finish process, not nearly as durable as black chrome however but far less expensive.
Choose wisely.