18 karat gold, silver, colored diamond and diamond 'Sliding  Necklace ', René Boivin, France. Photo Sotheby's

The 'day-to-night' style with three frontal panels set with round diamonds of yellow and brown hues weighing approximately 4.45 carats, the central panel set with round near colorless diamonds weighing approximately 5.50 carats, with polished gold rondelles which slide to conceal the diamonds and expose silver segments for variety of wear, gross weight approximately 99 dwts, internal circumference 13½ inches, signed René Boivin, stamped G & Co. with British import marks and French maker's marks; circa 1975. Estimate 30,000 — 50,000 USD

Note: For a bracelet of similar design see René Boivin: Jeweller by Françoise Cailles, page 367.

Sotheby's. Magnificent Jewels, New York | 29 Apr 2014 - www.sothebys.com