An oxide finish is accomplished when a black finish is applied to metal. Sometimes the entire surface is coated and, for a different effect, the high areas are rubbed off leaving the oxidation in the engraving or embossing. This can be achieved by using a liver of sulfur or platinum chloride dip.
Brightly polished 14 karat yellow gold Neo-Classic style bezel earrings, highlighted with ruby cabochons are the frames for the pair of replica ancient coins encased. The coins, having an oxidized finish, depict the profile of a Greco-Roman Emperor.
Image courtesy of Lang Antiques.