An unusual Art Deco diamond and portrait-cut diamond cocktail watch, 1920s, the rectangular silvered

An unusual Art Deco diamond and portrait-cut diamond cocktail watch, 1920s, the rectangular silvered dial covered by a portrait-cut diamond measuring approximately 7.5 x 5.3 x 1.7mm, to an openwork rectangular mount millegrain-set with rows of single-cut diamonds, mounted in platinum with foliate engraving to the gallery, to a black fabric strap, case width 1.5cm, manual winding movement, signed Lusina, spare expandable watch bracelet stamped 18CT