There was at one time considerable controversy as to whether stamps should be collected used or postmarked, and even now the question occasionally crops up in the philatelic magazines. It is purely a question of taste.
An unused stamp is evidence of the condition in which it was issued, while a used one furnishes proof that it has actually performed the duty for which it was intended, viz., franking a letter or other article of correspondence.
From the sentimental point of view, one would plump for the postmarked stamp, for this has travelled possibly from one end of the world to the other. The beginner will be well advised to take unused or used stamps, just they come along.
There is a world of interest in the postmark. In many cases, it bears the name of the place of posting and the date, and such postmarks are often valuable evidence of the earliest period at which a particular variety was used. Sometimes the office of posting is indicated in a kind of code. For example, the numbered and lettered postmarks of Great Britain. Sometimes a particular postmark will prove that the stamp of one country has been used in quite another part of the world.
Many pages of the Stanley Gibbons catalogues are devoted to postmarks which denote the use of certain British stamps in various parts of the world, while Indian postmarks may be found indicating stamps used at certain offices quite outside of the country. Such classes of stamps are denoted by the term "used abroad."
In modern time the postmark often carries an advertisement in addition to the date and place of posting. Sometimes the advertisement is even illustrated pictorially and quite an interesting collection of advertising postmarks may be made.
It is usual to assume that all stamps cancelled in pen and ink are fiscals, which have been used on receipts of documents. But this is not always the case.
The early stamps of Venezuela, for example, were postmarked by a pen marked scribble. Afghanistan, at one time, was even more drastic, for here "postmarking" was done by chopping a piece out of the stamp with scissors.
Pre-cancels are postmarks printed on the stamps before they are sold to business forms who use large quantities of them, thus saving the labour of postmarking each item of correspondence separately. Such pre-cancels are in regular use in Canada and the United States and quite a number of collectors make a special study of them. Luxembourg ad other countries have also used this system.
Special postmarks are often used in connection with exhibitions, or to commemorate some special event, quite apart from the advertising postmarks already mentioned. In other cases, the different arrangement of the postmark may be studied. A country may first use an arrangement of bars, then dots, and later the ordinary circular postmark, all these being of interest to the collector who studies his stamps.
The earlier issues of Great Britain and Canada, too name only two countries, are prolific in differences of this kind.