In watchmaking, polished is not a neutral surface state: it's a design choice that determines how light moves across the object. A polished surface reflects light directionally and specularly; a matte or brushed surface diffuses it. The contrast between the two is almost always intentional, and understanding it changes the way you read a watch.
The most extreme finishing is mirror polish, achieved through successive stages of increasingly fine abrasives until the final hand-finishing. The result is a surface that reflects like a flat mirror. You find it on case flanks, lugs, and bracelet center links. On the Rolex Oyster, for example, the mirror-polished center links contrast with the brushed outer links: the effect is that the bracelet seems to come alive when you move your wrist. The same principle underlies the gadroon pattern on the 1970s Piaget Polo: alternating polished and brushed grooves that punctuate the case and bracelet with precise rhythm. I've held many Polo 79s in my workshop; that interplay of finishes still holds up today.
Anglage polishing is a specific case: only the beveled edge of bridges and plates is polished, leaving the flat surfaces sandblasted or grained. The contrast is millimetric but perceptible to the naked eye, and in backlighting it becomes sharp. In high-end movements—but also in certain more accessible timepieces like the Holthinrichs Deconstructed—this work is still done by hand, with wooden sticks and diamond paste.
On the dial, polished finishing takes different names: glossy, mirror-like, Grand Feu when it's enamel fired at more than eight hundred degrees. Grand Feu enamel has an optical depth that no industrial lacquer reproduces; the dial seems to have volume even though it's flat. Rhodium plating, on the other hand, is a galvanic treatment: an extremely thin layer of rhodium deposits a white-gray, hard and brilliant surface, often used as a base for high-end watch dials.
Multi-level finishing—polished case, brushed bezel, polished screws on the sides—is the standard answer to monochromatic aesthetics: without color contrast, light contrast becomes the only available visual grammar. It's not a trick: it's design.