Swiss 18K gold, enamel and paste-set pendant watch Circa 1780

Gold verge with the portrait of a lady
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A fine and rare Swiss 18K gold, enamel and paste-set pair-cased pendant watch, circa 1780. Outer case: two-body, the back with painted on enamel portrait of a lady with paste-set highlights, paste frame, translucent imperial blue enamel border with gold paillon foliage, the band engraved with a repeated pattern, paste-set front bezel. Inner case: polished. White enamel dial, radial Roman numerals, outer minute track with five-minute Arabic numerals and gilt Louis hands. A hinged, gilt full-plate movement with pentagonal baluster pillars, fusee and chain, verge escapement, brass balance with flat balance spring, single-footed cock with ruby-paste endstone, silver regulation dial. Dial and movement signed. 
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Diameter: 36 mm
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Signed: Abraham Colomby Geneva
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The case missing pearl(s)/stone(s).