To keep the shiny, pristine brass appearance of new metal, you can use a brass cleaner such as Brasso to revive the original finish. If upon opening your fixture, you note spots, it may have darkened in the warehouse. While this isn’t something we love, it does happen naturally from being boxed and stored. If you want to reset the aging process start off by polishing with Brasso (or similar) first.
For day-to-day care, simple dish soap, or an organic cleaner will remove debris or smudges from dirty hands. A soft cloth, like microfiber or a paper towel, will buff it to a shine. Acidic kitchen substances (lemons or tomatoes) or bathroom staples (like toothpaste) can increase the rate of the tarnishing process. In these instances, you'll need brass polish. Simply rub some onto a soft cloth, wipe in an upwards motion, rinse with water, and dry to keep your faucet looking its best.
Brass is going to change eventually, no matter what you do, but you can keep it looking like the day you bought it longer by polishing it frequently.
There's one important detail to note if you turn to brass polish: Most formulas are corrosive to some countertop surfaces, like marble or wood, so be careful not to overdo it, especially around the escutcheons that join the faucet to the countertop. As a rule, we don’t recommend DIY mixtures, which can be abrasive and scratch the finish.
Depending on how much of a patina you want, unlacquered brass kitchen faucets can be polished twice a year or as often as once a month. If you find your unlacquered brass faucet tarnishes more quickly than you'd like, you can also consider coating it with carnauba car wax, which will seal the surfaces (and reapply as it wears off). With proper care, unlacquered brass should last more than a lifetime.