British Guiana 1 Cent Black on Magenta

British Guiana One Cent Black on Magenta, 1856 was considered to be the world's rarest and most expensive stamp. The stamps were printed on poor quality paper in black ink on magenta coloured paper. There’s only one in the world known exist, so this stamp was unique, as no other copy was ever discovered. In 1980 it was auctioned to John Dupont for $935,000.