An antique hardware finish is not just a color; it's a clue to when the piece was made. Different metals and finishes moved in and out of use by period, and learning them helps place a fitting in time.
The warm metals came first
Brass and bronze carry the earlier eras. Bronze, harder and often darker, appears in the best Victorian hardware, cast into deep ornament and left to develop a rich patina. Brass, brighter and softer, runs across a huge span of hardware and lighting, and its natural aging, darkening in the recesses, brightening where hands touch, is one of the most recognizable signs of an old piece. Both are solid metals through and through, which is why they age honestly and can be brought back rather than refinished.
Then the cool platings
Nickel and chrome mark the shift into the twentieth century. Nickel plating, a bright, cool, silvery finish, came into favor in the early 1900s and looked clean and modern against the warm brass of the era before. Chrome followed, harder and brighter still, and belongs strongly to the Deco and Streamline periods. Plating adds a wrinkle worth knowing: nickel and chrome are usually thin platings over a brass or steel base, so they wear through at the high points, exposing the metal beneath. Solid brass and bronze don't have that layer to lose.
Salvager's Note: Warm metal (brass, bronze) generally reads earlier; cool plating (nickel, chrome) reads later, roughly 1900 on. If the finish is wearing through to a different metal underneath, it's plated, not solid, which changes both age and how you restore it.