Late 1930s platinum and diamond tank cocktail ring

Late 1930s platinum and diamond tank cocktail ring. Centrally set with a rectangular step cut diamond in a channel setting, flanked to either side with an additional four smaller rectangular step cut diamonds in channel settings, centrally set to top and bottom with two semi-circular fancy cut diamonds in rubover settings and further decorated with round old cut diamonds in grain settings, to a chunky geometric bow motif with open architectural gallery and broad trumpeting shoulders embellished with tapering baguette cut diamonds in rubover settings, terminating to a solid shank. Marked platinum and iridium.