I have one word of instruction for you: DON’T!! And if you must polish, DON’T lacquer it. And here’s why.
First of all, you’ll greatly decrease the value of your item. Many antique dealers and collectors won’t purchase a chandelier that’s been polished and lacquered. Second — Shiny brass? It went out with the 1980’s. (Would you wear three-inch shoulder pads to work? No? Then don’t polish your chandelier like that.) The patina on your antique piece is a significant part of its history, and once it’s gone, it takes years to get it back. If you lacquer it, you’ll never get it back unless the item is stripped.
There’s one instance in which I do recommend polishing: If you have a silver plated chandelier, you can really improve its appearance by careful polishing.
If you’re dealing with antique door hardware, be very careful not to over-polish. And re-plating a piece with a brass or bronze finish is almost never a good idea — you might make it indistinguishable from a reproduction. Some well-meaning people, eager in a quest for bright shiny hardware, take 1880’s bronze doorknobs and wirebrush them for an all-over bright effect. When this is done, you’ve not just lost the patina — you’ve lost the way the piece was originally supposed to look. Most antique door hardware, from the 19th Century to the 1930’s, had a cool two-tone effect — the background was darker than the details, allowing the details to really stand out. If you want to shine up hardware with a brass, bronze, or copper finish, the best thing to do is to touch up the highlights with some brass polish and some very fine steel wool. Go slowly — you can always do a little more later if you need to, but it’s very hard to undo what you’ve done.
So take care of your antique pieces, enjoy their beautifully aged finish, and be proud that they are antiques! If you want shiny brass, you can always go to Home Depot.