I was delighted when the US Postal Service put out its sheet of American Expressionism stamps in March: Hans Hoffmann, Mark Rothko, Clyfford 
Still, Barnett Newman, Robert Motherwell, Adolph Gottlieb, Arshile Gorky, Willem de Kooning, Jackson Pollock and Joan Mitchell. They're gorgeous and, for stamps, huge. But something definitely goes wrong when the stamps are used, as this postmarked Rothko I got in the mail shows. (I suppose it could work for Jasper Johns, perhaps!)