Exceptionally rare Ostertag convertible jewel, France, circa 1920s, showcasing innovative period engineering. Crafted in platinum (French hallmarked) with superb French pavé and millegrain work. Set with an extraordinary diamond suite: 26 larger European rose-cut diamonds totaling approx. 9.30 ctw (mixed F/G/H and K/L colors, VS/SI) plus 148 graduated smaller European rose/round-cut diamonds totaling approx. 7.56 ctw (G/H color, VS/SI). Centered with a millegrain bezel-set cornered emerald-cut Colombian emerald (8.5 x 5 x 4mm; approx. 1.23 ct) and framed by 14 calibre-cut Colombian emeralds in millegrain bezels totaling approx. 2.15 ctw. Weight 30.95 grams; measures 66 x 40 x 10mm. French marks including maker “RF,” platinum hallmarks, and signed “OSTERTAG FRANCE”. Very good conditions. All our diamonds and colored gemstones are naturally earth-mined. Any synthetic (lab-grown) stones will be clearly indicated in the description. Upon Request, Auction House may provide an appraisal. This will carry an additional cost. Appraisals are made by our in house GIA certified Gemologist.