My side locks have blacked out brass to reduce glare while hunting. However, most brass polishes, at least Brasso for sure, has tarnish resistors built in. If you polish with something else, like valve compound, it's probably cheaper, but you'd have to find a different compound to resist the tarnish. You could probably clear-coat it, which would slow down tarnishing, but might begin to slough off after a while and need reapplication.