There is the paper on which it is printed, the design, by which we usually mean the pictorial part of the stamp, the inscriptions, or lettering and figures of value, the ink with which the design is printed, varying in colour, the gum, and the means of separation i.e. the perforation.
The paper may be further examined as to its watermark, texture, and surfacing, and sometimes, colour.
The main classes of paper with which the collectors should be familiar are called wove and laid.
A wove paper has an even texture without any particular distinguishing features, as a very large portion of the existing postage stamps are printed on paper belonging to this class.
Laid paper, when held up to the light, shows parallel lines of greater or less width running across the stamp. Russia provides any owner of a general collection with examples of stamps on both types of laid paper. Other classes of paper sometimes met with include pelure paper, the official definition of which is "a very thin, semi-transparent paper, about the thickness of tissue paper, but much harder and tougher."
Granite paper has tiny specks of coloured fibre in it, which can usually be seen with the naked eye. Some quite common stamps of Switzerland, the issue of 1882-98, furnish a good example of this paper, though they were also printed on wove paper.
In the paper on which some stamps are printed, there is a watermark. This consists of a device formed in the texture of the paper itself and can be usually seen when the stamp is held up to the light. If the watermark cannot be seen in this way, it will probably show up when the stamp is placed face downwards on the black polished surface of a watermark detector.
Single watermarks are often arranged so that one device falls on each stamp in a sheet. There are cases where they are placed close together so that parts of more than one watermark fall on each stamp and those are known as multiple watermarks.
There have also been instances where paper prepared for printing sheets of a certain size of a stamp has been used for stamps larger or smaller in which case the watermark will fall irregularly. There are often watermarks, usually consisting of inscriptions, on the marginal paper surrounding the sheet of stamps and those are known as marginal watermarks.
The surface of the paper
The surface of the paper is often specially prepared, sometimes with the object of getting a good surface on which to print, at others to prevent postmarks being cleaned from used stamps, so that they may be used again.
Chalk-surfaced paper or coated paper belongs to the latter class, as any attempt at cleaning brings away the preparation with which the paper is coated, at once altering the appearance of the stamp. A test for chalk-surfaced paper is to touch slightly the surface of the stamp with the edge of a silver coin.
The colour of the paper may be due to its being dyed during manufacture, or the colour may be applied to it by a process something like printing, in which case it will be coloured on only one side. This is known as surface-coloured paper or "white back."
Many of the earlier French and French Colonial stamps have the colour only on the surface, in this way, while the "white backs" of some of the British Colonies are familiar to most collectors.
The characteristics of the ink used in printing the design are not likely to trouble the ordinary collector, but its colour is important. The colours in which stamps are printed often cause confusion to collectors, chiefly because there is no recognised system of naming them, even if we could be sure that any two collectors see the same colour alike.
Thus one catalogue will describe the colour of a certain stamp by one name, while another will give a totally different description. Description in print is not of great assistance, but the Colour Guide is as helpful as anything at present available to the collector, as it shows 100 different standard colours or shades, and names them in a way that comes near to meeting general acceptance.
The term "shade" also requires explanation. A stamp is printed with the fixed intention that, so far as is possible, every copy of it shall be in exactly the same colour and in the same depth of that colour. But printer's ink is curiously wayward stuff.
Apart from unintentional variations from mixing it, it may be affected by the amount of moisture in the atmosphere during printing or drying or by the temperature of the air-- variations in these other aspects give rise to variations in colour, which are called "shades" by philatelists.
Early stamps were issued in sheets in which no provision was made for easily separating stamps. Scissors had to be resorted to. Then came the perforating machine, whose pins produced regular lines of holes between the stamps, so that their separation was easy.
But the arrangement and spacing of the holes were not always similar, even in stamps of the same issue, and as such differences usually proved the use of a new or altered perforation machine, they came to be of interest to collectors, as they often helped to fix the date or period when particular stamps were issued.
Some method was, therefore, necessary for indicating the arrangement of the holes, and as these were usually spaced regularly, it was decided that the number of holes in a space of two centimetres should indicate the perforation of a given side of a stamp. Thus the description "Perf. 15" does not mean that there are 15 perforations on every side of a stamp, for naturally, the longer side would have the most holes, but that, in any space of two centimetres on any side of the stamp, you will count 15 holes.
Where the spacing varies on different sides of the same stamp, the perforations are said to be compound. Opposite sides usually have the same spacing, so that when you read "Perf. 15x14" you will know that the first figure given is the gauge of the top and bottom of the stamp, while the second is that of the left and right sides. The figure for top and bottom always comes first.
A perforation gauge very soon enables the collector to tell the correct description of the perforation of any particular stamp. Successive spaces of two centimetres are divided by dots which exactly fit the holes on the side of the stamp whose perforation you are measuring.
Lithographed stamps are printed from an absolutely flat surface so that the ink of the design lies smoothly on the surface of the stamp, the characteristics of stamps printed by this method being a flat, smooth appearance.
Typography stamps or surface printed stamps are those stamps printed from the raised portions of the type or printing plate. It is these portions which represent the design of the stamp and which receive the ink during its transfer onto paper. The pressure used during the printing tends to indent the design into the paper.
Line-engraved stamps, recess-plate printing or printing from intaglio plates, as the third process is variously called, is the reverse of surface printing. The design is cut into the plate while the ink lies in these cuts, into which the paper is forced during printing, to pick up the ink. The design is this raised on the surface of the stamp and the lines of ink can often be seen standing up in minute ridges.