Rock crystal and diamond 'Clou' brooch, René Boivin, 1930s. Photo courtesy Sotheby's

The carved rock crystal designed as three stylised nail heads, each inset with a cushion-shaped diamond, accented at either side with a double row of rose diamonds, French maker's mark and partial French assay marks. Estimation  10,000 — 15,000 CHF 

Litterature: Cf: Françoise Cailles, René Boivin Joaillier, Paris, 1994, pages 109 and 124 for a photograph and a drawing of a related brooch designed by Boivin in 1932.