An 18ct white gold and amethyst tank ring, by Cartier, the square amethyst with slightly cabochon crown and facetted pavilion tension set in white gold angular mount, shank signed ‘53 Cartier 1997, 750’ and numbered ‘K38494’, with French eagle’s head guarantee mark and lozenge-shaped maker’s mark, in Cartier case, ring size M½. £600-£800