Highly unusual Swiss gold and chrysoprase lever Circa 1916

Open faced lever watch by Patek Philippe
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A highly unusual Swiss 18 carat gold and chrysoprase open faced keyless lever watch with custom made American case, circa 1916. Ultra thin nickel finished lever movement, 18 jewels, bimetallic compensation balance, wolf’s tooth winding. Associated gold cuvette with engraved inscription Burton G. Tremaine June 28th, 1917. White enamel dial with Roman numerals, blued steel moon style hands and subsidiary seconds. In associated custom made American case with finely chased and engraved garland decorated band and bow, hinged reverse set with an octagonal translucent green chrysoprase plaque with engraved classical scene in high relief, surrounded by a gold floral decorated border. Movement and dial signed.
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Diameter: 45 mm
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Signed: Patek Philippe & Cie Geneva Switzerland