Maintaining polished brass outside is a continuous maintenance job.

Unless, of course, you get Balwin Brass.

When I purchased a new home ten years ago, I replaced all the outdoor lights
and front door hardware with Baldwin Brass 003 Lifetime Polished Brass
Finish. It's just as shiny now as the day I installed it. About every
three years or so, I wash off the dust with a glass cleaner and water, and
then hand dry. The finish is always shiny gold. No polishing necessary.

The 003 finish does not use a lacquer like most brass fixtures. Instead, the
brass is nickel plated and then the final finish is applied in a plasma
chamber for a molecular bond. Each lighting fixture was about $300 and the
pair of front door hardware was about $500. Not cheap, but they will look
brand new for decades, and no polishing needed.

Best,
Christopher