French single-handed oignon watch with alarm Circa 1720

Silver open faced verge oignon watch by Sourdeval
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A very fine and rare French silver open faced single-handed verge oignon watch with alarm, circa 1720. Hinged, fire-gilded full plate movement with divided Egyptian pillars, fusee and chain, verge escapement with steel balance and short balance spring, cock pierced and engraved with birds and foliage, Bosley type regulator, alarm with fixed engraved brass barrel and steel train, sounding on a bell by both ends of short T-shaped oval hammer. White enamel dial, annular with Roman numerals, inner quarter-hour ring, winding apertures at 4 and 8, centre with brass alarm disc with Arabic numerals and steel pointer indicating hours, blued steel arrow alarm setting hand. Polished case with pierced cartouches for sound, inner bezel pierced and engraved with foliage, square hinge, loose ring pendant. Movement signed.
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Diameter: 60.5 mm
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Signed: Sourdeval à Paris