Fancy coloured sapphire, rock crystal and diamond brooch, 'Pont', René Boivin, circa 1930. Estimate 40,000 — 59,000 CHF. Photo Sotheby's

Of bombé design, set with cushion-shaped coloured sapphires, between lines of circular-cut diamonds, the edges composed of polished rock crystal, signed R. Boivin. 

Bibliography: Cf.: Françoise Cailles, René Boivin Joaillier, Paris, 1994, pg. 117 for a similar clip 'Pont' set with diamonds. 

Sotheby's. Magnificent Jewels and Noble Jewels, Genève, 11 nov. 2015, 10:00 AM