French gold and enamel watch with visible balance Circa 1810

Gold and enamel open faced cylinder watch by Jean-Pierre Gregson
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A fine French 18-carat gold and enamel open faced pocket watch with diamond set visible balance, circa 1810. Case rim engraved and enamelled with opaque polychrome, to the back translucent cobalt blue enamel over engine turned ground, casemaker’s punch mark IM. Peripheral enamel dial with Roman hours and Arabic quarters, diamond set visible balance and double gold serpentine hands. Gilt frosted full plate movement, blued screws, keywind, cylinder escapement, balance bridge, and regulator scale. Movement signed.
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Diameter: 51 mm
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Weight: 76 g
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Signed: Gregson à Paris