Retro Three Stone Engagement Ring in Platinum and Yellow GoldRetro Three Stone Engagement Ring in Platinum and Yellow Gold. This lovely Retro three stone engagement ring features 1. 61 carats of Old European cut diamonds set in platinum and 18 karat yellow gold. The diamonds are set neatly with flat prongs on the outside and shared prongs between. Below the platinum diamond section, the ring transitions to a smooth and polished yellow gold shank for some nice contrast.