Old-Fashioned Values: Vintage settings and stones are hipper ... three-and-a-half-carat emerald-cut style from Louis Glick. Solitaire Pursuit: A single stunning stone is all a classicist needs.

"When you think of a traditional solitaire engagement ring, elongated diamond shapes such as emerald or oval cuts will be set 'north-south' or vertically," explains the jeweller Rachel Boston. "An ...