French gold watch with special enamelling technique Circa 1780

Gold and enamel verge watch 
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An exceptionally fine French 18 carat gold and enamel open faced Louis XV style pocket watch with special enamelling technique, circa 1780. Gilt full plate movement with a verge escapement a plain flat three arm balance, decoratively pierced balance cock engraved with scrolling flowers and a silver regulation disc. Both bezels are set with faux mother of pearl half pearls, the case back with extraordinary polychrome enamel work showing a raised putto and flowers on a translucent dark red guilloché ground. White enamel dial with radial Roman hours, an outer minute track, outer Arabic five minute numerals and probably original Louis XV hands. Case numbered. Movement signed and numbered
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Diameter: 39 mm
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Weight: 46 g
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Signed: Berthoud à Paris