Two coins can share a design, a metal and a weight and still look nothing alike, because the finish decides how the surface reads. Colorized and antiqued treatments are the most common here, often combined on the same piece.

Finish also affects how a piece grades. An antiqued coin is judged on the evenness of its patina, a proof on the contrast between mirrored field and frosted device. Graders assess each against its own standard rather than one universal scale.

Our guide to coin finishes explains how each treatment is achieved and what to look for in each.