The German zeppelins were of much interest during this period, and in 1930 the Department issued special stamps to be used on the Pan-American flight of Graf Zeppelin. Although the Graf Zeppelin stamps are today highly prized by collectors as masterpieces of the engraver's art, in 1930 the recent stock market crash meant that few were able to afford these stamps (the $4.55 value for the set represented a week's food allowance for a family of four). Less than 10 percent of the 1,000,000 of each denomination issued were sold and the remainders were incinerated (the stamps were only available for sale to the public from April 19, 1930, to June 30, 1930). It is estimated that less than 8 percent of the stamps produced survive today and they remain the smallest U.S. issue of the 20th century (only 229,260 of these stamps were ever purchased, and only 61,296 of the $2.60 stamp were sold).[citation needed] In 1932, a set of 12 stamps was issued to celebrate the George Washington's 200th birthday 1932 Washington Bicentennial. For the 2¢ value, which satisfied the normal letter rate, the most familiar Gilbert Stuart image of Washington had been chosen. After postal rates rose that July, this 2¢ red Washington was redesigned as a 3¢ stamp and issued in the purple color that now became ubiquitous among U.S. commemoratives.