Unusual Swiss platinum, sapphire and diamond brooch watch Circa 1910

Platinum lapel watch made for Black, Starr & Frost
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A fine and unusual, platinum, sapphire and diamond-set, keyless lapel watch with articulated integral diamond and ruby-set brooch, circa 1910. Made for Black, Starr & Frost by Ed. Koehn, Genève, Switzerland. A solid, polished case, hinged case back, bezel pave-set with rows of diamonds and rubies, the corners set with four pear-shaped diamonds. Matte silver dial with painted Arabic numerals, outer minute track and blued steel spade hands. A tonneau, rhodium-plated movement, sixteen jewels, straight-line lever escapement, cut bimetallic compensation balance adjusted to seven positions, blued steel flat balance spring. Case signed Black, Starr & Frost, movement signed Ed. Koehn, Geneva, Switzerland.
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Dimensions: 14 x 25 mm
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Thickness: 6 mm
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Signed: Ed. Koehn  Genève