David Webb Impressive over 10TCW Diamond Black Onyx Necklace in 18K Gold Designer: David Webb Stones: Black Onyx and Diamonds Diamonds: approx. 10 TCW VS Clarity / G Color Metal: 18k Yellow and White Gold Weight: 222 grams Length: 16” Width: 26 mm at the widest point Condition: Pre-owned. Very Good. Hallmark: David Webb. 750.