A diamond, coloured diamond and enamel ring, early 20th century and later, centring on a

A diamond, coloured diamond and enamel ring, early 20th century and later, centring on a marquise-shaped diamond of brownish yellow tint weighing approximately 0.50 carats, within an elongated navette-shaped mount set with circular- and square step-cut diamonds, each end with a pear-shaped section of black enamel, mounted in platinum, size M1/2, shank and enamel possibly later