fine French gilt and enamel verge watch with portrait Circa 1790

Gilt and enamel watch set with zircons
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A French gilt metal key wind open faced pocket watch with Vernis Martin portrait, Paris circa 1790.
Gilt full plate fusee verge, pierced and engraved balance bridge, silver regulation disc, square baluster pillars and a plain three-arm gilt balance.
White enamel dial with black Roman numerals interspersed with zircons, black outer minute track with Arabic numeral 5 minute markers, winding aperture at 2, gilt hands.
Consular case form with applied three colour gold bezel foliate decoration, portrait to reverse in Vernis Martin after a self-portrait of Rubens, diamond set push piece, D shaped bow
The dial bears the inscription Gudin in script and Fres Melly à Paris, while the movement is also marked with Fres Melly à Paris. 
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Diameter: 44 mm
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Signed: Freres Melly à Paris
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The oval portrait to the reverse is strikingly similar both in the detail and colour to the two self-portraits painted by Rubens, one of 1622 in Windsor Castle and the other, originally given by the artist to the Provencal antiquary Nicolas Fabris de Peiresc in 1628, now in the National Gallery, Canberra, Australia. It is, highly unusually for a small object such as a watch, painted in Vernis Martin, this having a degree of blistering very similar to that often found on oil paintings. Vernis Martin is a lacquer substitute perfected by the French martin brothers generally found on highly sought after late eighteenth century painted furniture.