An art deco fancy-coloured diamond single-stone ring, circa 1925. Photo Bonhams

The step-cut fancy greyish-blue diamond, weighing 1.85 carats, within a single-cut diamond gallery and baguette-cut diamond shoulders,ring size L, fitted case by James Rogdens & Son Ltd - Estimate: £30,000 - 50,000, US$ 49,000 - 82,000

Accompanied by a GIA certificate stating that the diamond is fancy greyish-blue, natural colour, VS2 clarity. Certificate number 2135437833, dated 14th June 2011.

Bonhams. Fine Jewellery, 21 Sep 2011. New Bond Street www.bonhams.com