Factors in stamps which the collector requires to examine are: (I) Paper, its colour, texture and watermark (if any) ; (2) design, subject, character of the impression (typographed, lithographed, engraved or embossed) and colour; (3) gum; (4) margins or gutters, with particular reference to the perforation (if any).
Watermarks in stamps are of great variety. In some cases an elaborate or large design is "watermarked in the sheet," and only part of it shows on a detached stamp. Where the water marked devices are small, and correspond with the arrangement of the stamps in a sheet, they are "single watermarks." "Mul tiple" watermarks are small and separate devices as in the "single," but set so closely together that parts of two or snore show in each stamp.
Perforations are punched out of the paper along the gutters between the stamps on a sheet. If instead of being punched out they are merely pricked by a wheel or raised printer's rule they are called "roulettes." Perforations and roulettes are measured on a system based on the number of perforations made in a length of 2 cm. (20 mm.). Thus, if a stamp be described as "perf. 12" it means that there are 12 perforations to the 2 cm. along any of its margins. To save counting a gauge is used consisting of a printed range of dots and lines set within a column 2 cm. wide. By running the stamp up or down this gauge it is easy to find a line where the dots fit neatly into the curves of the perforation; the number at the side denotes the perforation measurement.
The Scope of Philately.—The specialist seeks to show in his collection the full history of the stamps under consideration. Where obtainable he will show the artist's original drawings, engravers' and printers' proofs, colour trials, essays (proposed stamps which were submitted, but rejected, or altered before adoption). The principal portion of the collection, however, con sists of the actual stamps as issued and used. Good condition of the specimens is of first importance. Unused stamps should be as near "mint" or "post-office" state as possible, that is to say, in the state they were in at the time of manufacture and issue. Used and unused stamps, especially old imperforate issues, are much sought after in unsevered pairs, strips or blocks, in which state they are often of added value. Used stamps of early date are of special interest if preserved on the original letter or enve lope. The philatelist distinguishes successive printings or editions of stamps of one type by variations in shade, impression, paper, watermark or perforation. Postmarks, especially where they bear dates, help to place such editions in their proper sequence. Various
phases of the use of the stamps are illustrated by postmarked copies, including, in many cases, stamps of one country used in another; e.g., "British used abroad," also French, German, United States and other stamps used extra-territorially.
The World War provided interesting issues, like the British and other war issues for Samoa, New Britain, Baghdad, Bushire and Togo. The period of the armistice and post-war reconstruction brought many new countries within the sphere of philatelic inter est, e.g., Estonia, Latvia, Lithuania, Czechoslovakia, etc., and produced stamps which serve to recall the plebiscites, the man dated territories and the League of Nations; while in 1929, the issue of stamps which the Papacy formerly made, was restored. With the advancement of aeronautical transport, mails are now regularly sent by air along many routes, and since Italy issued a special stamp for use on letters sent by an experimental air-mail between Rome and Turin in May 1917, the United States, Austria, Germany and many other countries have issued airpost stamps.
In addition to interesting the general stamp collector, these have attracted new collectors who limit themselves to stamps of aero nautical associations. They pay particular attention to "flown covers," i.e., letters or cards actually sent by air-mail. Such letters carried on historic flights like the transatlantic flights by Hawker (April 1919), Sir J. Alcock (June 1919), Marquis de Pinedo (1927) command high prices; there are elaborate special priced catalogues of air stamps (see Bibliography).
Expressions other than those used in a strict dictionary sense are : Bisect, half a stamp used as half the value of the whole stamp. Block, an unsevered group of stamps. Control, a letter or number, or both, on margin for checking purposes, or a device stamped on the front or back to prevent forgery or misuse. Error, an incorrect stamp, either in design, colour or paper, etc. Essay, a proposed stamp, not adopted, or adopted only after some modification. Imperforate (imperf.), without perforation. Local, a stamp whose validity is limited to a town or district. Mint, in perfect unused condition (in the United States the same is de scribed as Post-office state). Pre-cancel (led), stamps sold by the post-office already cancelled to firms mailing postal matter in bulk. Reprint, a fresh printing from original plates or stones after an issue has become obsolete. Surcharge, an overprint affect ing the designation of value. Tete-beche, an unsevered pair of stamps, one being upside-down.