All the stamps must have the indication, normally in Latin letters, of the emitting country. There are a few exceptions, as in the case of Great Britain.

The first stamps were not perforated (indented) and they had to be cut off from the stamp sheets with scissors, until 1847 when the Irish Henry Archer invented a perforation machine to facilitate this splitting.

Even this perforation method begun in 28JAN1854 in England, it was only in the year of 1867 that the first perforated sheets were sold in the Portuguese Market. When separate the stamp from the sheet was then called of " indented " the edge of the stamps. But not all the indented ones were equal. According to the emitting Country or the stamps emission, the number of the holes in one given measure is different, existing cases where one stamp has different indented in each side, or only at the left and right side. Sometimes two or more stamps may look alike, but each may have a different perforation type and / or size. The perforation is important to determine and identify which stamp is which.

There are different types of perforation. The most current ones are of 3 types: in a line, comb type or grid. The first method perforate the sheet in a line, the second allow us to use simultaneous perforation lines in perpendicular, and making at the same time the holes in three sides of the stamp, and the last one – actual method - using a grid of cutting punches will perforate once all the stamps in a sheet.

The Frenchman August Legrand idealised a system to measure the holes, called “Perforation Gauge”, that consists of determining the number of the holes in two centimetres’ wide. When it is mentioned in the Catalogue only a number to indicates a perforation, which means that the indented is equal in both sides of the stamp. If, for example the expression will be of 13 x 12 indicates that it has 13 holes in the horizontal and 12 in the vertical line.

Perforation gauge

The relative position of a stamp’s design in relation to the margins surrounding it. Due to the diverse printing methods used during the first years many emissions were deficient, which caused a lot of stamps with deficient margins. Centring is a very important consideration in determining a stamp’s value.

In brief words, give us an explanation of the main subject of the stamp. Allusive legend to the stamp.

In the inferior part of the stamp it presents an indication of who it drew the stamp or it manufactured the engraving. Actually also includes the year of the emission. In the stamps issued from 1895 to 1937 some of the emissions mentioned in the end of the stamp only the name of the designer.

The face value is the acquisition price of the stamp during the period of its postal validity.
In accordance with international agreements, the face value printed in the stamp should be express in Arab numbers (1 Escudo, 1 Pound, 1 Mark, 1 Franc). Several countries emit stamps without a specific face value, distinguishing them by a letter (A, B, C....) for identification of the tariff. Usually they are used in the changes of the value.

The drawing, or the vignette, is the design reproduced in the stamp and reflects the reason why the stamp was issued or dedicated..

It's a free criterion and the stamps are printed in polychromes, using the basic series with different colours to distinguish the face value.

The back of the paper is usually gummed to facilitate its adhesion to the letters, the postal packages or another type of mail. The gum is an integrant element of the stamp and cause serious problems to the Collector for being composed of chemical substances that a short term can cause oxidation, the deterioration and/or the destruction of the stamp.

The back of the stamps also served to print a control number of the units issued in a specific emission, as well as for printing of phrase(s) in different languages, allusive to the subject or respective emission.

The stamp’s dimension is indicated in millimetres. The first number mentions the horizontal dimension. Due to the several existing varieties and sizes, it would be almost impossible to describe here all its measures. In fact no government established a fixed rule, and most of them adopted the dimensions most appropriate to the use of their surmounting systems, for a better performance of the post office.

The known formats more used are: squares, rectangular, horizontal or vertical. Nevertheless it exists an infinity of stamps whose forms are work of a very peculiar imagination (hexagonal, round, triangular stamps and of irregular form).

The paper individualizes each specimen from one another by its distinct composition or elaboration. Currently phosphorescent and fluorescent papers are used due to the advantage of speeding the postal functioning through its complex machines.

The watermark is used in the paper pulps during its manufacture. Also known as “security paper”, it guarantees its authenticity making it difficult its fake.  The watermark is today of vital importance to know the series that belongs one definitive stamp. You can see this watermarks at backlighting.

All the graphical printing systems had been used so far for the manufacturing of the stamps. The most frequent are the following ones:

• Typographical
• Cacographic
• Lithographic
• Photogravure

Typographical: has its origin in the xylography, even has been born in the Renaissance. After become industrialized the primary material was changed from the wood to metal, as bronze or steel. Nowadays the basic material becomes the plastic or the linoleum. The stamps printed by typography are characterized for presenting in the back, in the form of relief, of the pressure exerted by the printer machine. Lines and dots form the drawing, with light colour as background. 

Cacographic (or “talhe doce”- sweet cuts – in Portuguese): This engraving system can only be done in metal. It is the best method for printing the stamp due the vastest variety of gotten colours, as well as for the relief of its characteristics. It is almost impossible to be faked, as the method used for engraving is unique and becomes impossible even for the person who has done the original. The method applied for this kind of engraving is reverse to the one used in the typographic system. This means that the part of the material removed from the metal with the burin, is fulfilled of ink and then printed on paper. The engraving of the cacographic system is done on zinc, copper or steel. 

Lithographic: It is the type of printing more displayed to reproduce an amount of varieties due to the biggest manual intervention and lesser mechanics. The artist draws in the rock or zinc as it is made in paper. The name of this type of engraving comes from the words lithos - rock, and graphos - to draw. All the inks used in this process are cloudy and the gotten colours have equal characteristics.

Photogravure: The reproduction of the original (through photographs or drawing) is gotten by photochemistry process using clichés. This is one of the processes most used currently; even it does not reach the artistic level of the systems based on the manual engraving.

They correspond to the stamps that, beyond the corresponding face value, it is printed another additional charge that was destined to collect funds for a specific Institution. Usually is for benefit of Social Institutions, Armed Forces, or the Anti-tuberculosis, or to the Red Cross. This idea comes from the Frenchman Gilbert Sersiron, during the international conference in Berlin in year 1902, and approved by all.

Brand new stamps perforated by Unofficial Institutions under Post Office authorization. The holes form letters, brands or legends of Commercial Companies, Private Institutions or Banks and were done to avoid illegal use of Stamps. It exists great collectors for these "punched" stamps. Some of these stamps with certain holes have higher values, as there are rare acronyms.