C. 1990 Vintage Bulgari Black Onyx Ring in 18kt White Gold. Size 7.5

18KT: Karat (abbreviated kt or K) is a unit that indicates the purity of gold in the metal. 18kt is 75% gold. In Europe, 18K yellow gold is most favored and used in jewelry.

WHITE GOLD: Gold is a precious metal which is naturally quite soft. To give it a white color and increase its strength, gold is alloyed with white metals, such as silver and/or palladium, and often plated with rhodium. The purity of the metal is indicated by a unit called a "karat," with 24kt having the highest percentage of natural gold.

ONYX: A favorite of the ancient Greeks and Romans, this gemstone adds a sophisticated shine to rings, necklaces, bracelets and earrings. A dyed form of chalcedony, onyx is most popularly found in black although it can be green, white or red, as well.

SQUARE: A symmetrical shape with four equal sides.

CABOCHON: A style of cutting gemstones to achieve a smooth, domed surface with an absence of facets.