one of wood. The United States produced one of plastic. East Germany issued a stamp of synthetic chemicals. In the Netherlands a stamp was made of silver foil. Bhutan issued one with its national anthem on a playable record. Graphic characteristics The subjects found on the face of postage stamps are generally what defines a particular stamp issue to the public and are often a reason why they are saved by collectors or history enthusiasts. Graphical subjects found on postage stamps have ranged from the early portrayals of kings, queens and presidents to later depictions of ships, birds and satellites, famous people, historical events, comics, dinosaurs, hobbies (knitting, stamp collecting), sports, holiday themes, and a plethora of other subjects too numerous to list. Artists, designers, engravers and administrative officials are involved with the choice of subject matter and the method of printing stamps. Early stamp images were almost always produced from an engraving—a design etched into a steel die, which was then hardened and whose impression was transferred to a printing plate. Using an engraved image was deemed a more secure way of printing stamps as it was nearly impossible to counterfeit a finely detailed image with raised lines for anyone but a master engraver. In the mid-20th century, stamp issues produced by other forms of printing began to emerge, such as lithography, photogravure, intaglio and web offset printing. These later printing methods were less expensive and typically produced images of lesser quality. Types Airmail stamp – for payment of airmail service. The term "airmail" or an equivalent is usually printed on special airmail stamps. Airmail stamps typically depict images of airplanes and/or famous pilots and were used when airmail was a special type of mail delivery separate from mail delivered by train, ship or automobile. Aside from mail with local destinations, today almost all other mail is transported by aircraft and thus airmail is now the standard method of delivery. Scott has a separate category and listing for United States Airmail Postage. Prior to 1940, the Scott Catalogue did not have a special designation for airmail stamps. The various major stamp catalogs have different numbering systems and may not always list airmail stamps the same way. ATM stamp — stamps dispensed by automates and have their value imprinted only at the time of purchase Booklet stamp – stamps produced and issued in booklet format Carrier's stamp. Certified mail stamp