An Art Deco diamond plaque brooch by Suzanne Belperron and Rene Boivin in the 'clou' design, the platinum mount set with a rectangular piece of rock crystal, inset to centre with two old cushion-cut diamonds of approximately 1.25 carats each, approximate colour / clarity H/I, VVS1/2, the stepped sides set with lines of old round-cut diamonds, in graduated rows of seven, six, and five diamonds, spaced with rock crystal batons, with unusual screw-catch to verso, 5.6 cm long, 2.3 cm wide, 18.5 grams. Bearing R.B. mark to side.