1908 saw the beginning of the long-running Washington-Franklin series of stamps. Although there were only two central images, a profile of Washington and one of Franklin, many subtle variants appeared over the years; for the Post Office experimented with half-a-dozen different perforation sizes, two kinds of watermarking, three printing methods, and large numbers of values, all adding to several hundred distinct types identified by collectors. Some are quite rare, but many are extremely common; this was the era of the postcard craze, and almost every antique shop in the U.S. will have some postcards with green 1¢ or red 2¢ stamps from this series. In 1910 the Post Office began phasing out the double-lined watermark, replacing it by the same U S P S logo in smaller single-line letters. Watermarks were discontinued entirely in 1916.