IWC, Cal. 8531, oversize, 18k yellow gold, made circa late 1950s,?a very rare two-tone guilloch? dial. The two-tone dial with detailed decorations and the massive oversize case of over 37mm solid 18-karat gold are very rare in the world where simple one-tone designs are often seen, and this is a rare example of an original taste rarely seen in the world It is.