While there are numerous types of perforated stamps, with anywhere from seven to 16 1/2 perforations in the space of two centimeters, there are really only three types of imperforate U.S. stamps. The first are those issued before 1857, when the first three-cent stamps bearing the profile of George Washington were printed by Toppan & Carpenter of Philadelphia and perforated using a rotary perforating machine manufactured by Bemrose & Co. of...Continue Reading