Something about stamp perforations
Comb perforation, line perforation, roller perforation, zigzag perforation, slit perforation. What types of perforations are there on postage stamps, what are the differences, and how are they measured?
Measuring tooth pitch
An international unit of measurement has been agreed upon for measuring perforation. It does not matter what type of perforation the seal has. It is simply determined how many 'teeth' there are in 2 centimeters. That number represents the perforation. So perforation 14 means 14 teeth in 2 centimeters, and perforation 9 means 9 teeth. To simplify counting and make it more accurate, perforation meters have been invented. In these, thin lines and/or dots indicate the number of teeth or holes. There are also 3-dimensional perforation meters where you can fit the seals against protruding points. Electronic perforation meters even exist. Below is an image of a Lindner Kombibox, a 3-dimensional perforation meter.
Because a different perforation size is sometimes used vertically than horizontally, a seal may have two different perforations, which are then indicated by two numbers. In this case, the first number always refers to the top and bottom sides, and the second number to the right and left sides. For example, with perforation 12:11, the top and bottom sides are 12, and the left and right sides are 11. If indicated by a single number, it means that all four sides have the same perforation. In the Netherlands, an 'x' is placed between the numbers for line perforation and a : for comb perforation. Internationally, it is frequently noted with a colon in between.
You now know how to measure and display perforations, but what types of perforations are there?
Line perforation
The simplest perforation, common in plate-printed stamps, but also in other printing methods. The sheets are perforated in lines, without regard for the transition between horizontal and vertical perforations. Consequently, line perforation usually results in uneven angles. Sometimes it may even appear as if a corner is missing, but if the perforation holes extend almost to the corners, this is normal. Some stamps exist in both line and comb perforations.
Equal
With comb perforation, a uniform perforation grid is used. In this case, the vertical and horizontal lines are aligned, ensuring that the angles of the stamps are uniform.
Roller perforations and roller seals
Perforated roll stamps were not sold in sheets at post offices, but in rolls. To make the rolls sturdier so that they do not break unintentionally at the perforations, some perforation pins were removed, creating 'bridges' in the perforations.
Only the Netherlands and Danzig have issued cylinder stamps with perforations. Most cylinder stamps are simply perforated on two sides and unperforated on the other two sides.
However, rolls of seals with perforations on all sides have also been produced. In that case, it is not unusual for the perforations on the outer sides to be shorter or sometimes even slightly damaged. See the example above with flattened perforations. With roll seals, this is not considered a defect.
Large holes / Small holes
The thickness of the pins used to create the perforations can vary considerably. Sometimes differences occur even within the same type of stamps, as shown above. There are also stamps with alternating large and small perforation thicknesses.
Imitation teeth
With imitation perforation, from a distance the stamps appear to be perforated, but the perforation is only printed using small dots, making it look as if we are seeing perforation holes.
Safety teeth
In safety teeth, the perforation is not continuous, but there is a break. This is often a wider, oval-shaped perforation, but there are also safety teeth with entirely unique shapes, as shown above.
Roulette perforation
In roulette perforation—for which the French term 'Percé en lignes' is often used—the sheets are scored with a rotary cutter.
Sawtooth perforation
Sawtooth perforation is also a type of roulette perforation, except that a serrated rotary cutter is used here. Unlike 'ordinary' perforation, where the stamps are separated by holes and the teeth of two stamps meet, with sawtooth perforation the teeth fit precisely into the 'holes' of the adjacent stamp.
Snake teething
The first stamps of Finland with serrated edges are famous. Actually, this is a rough form of sawtooth perforation.
Irregular serration
Actually, this speaks for itself. The pins used for the perforation were not neatly aligned, resulting in messy perforations.
Private or local perforation
Stamps that came onto the market unperforated for whatever reason were sometimes perforated by local post offices themselves for convenience. Famous are French unperforated stamps of Napoleon III; they were issued unperforated, but of which more than 30 different local perforations are known.
Gestanste tanding
Die-cut perforation occurs on self-adhesive stamps. Usually, only the stamp is die-cut and not the backing. Sometimes the backing is also partially die-cut, making it easier to detach from sheets including the backing. Fully die-cut stamps have also been released in the Netherlands for collectors. If the same stamp has been issued in both gummed and self-adhesive versions, the differences in used stamps can be seen at the ends of the perforations. On gummed, normally perforated stamps, the perforation is frayed, while on die-cut stamps it is smooth without fraying.
Ongetand
Many stamps were issued on the market unperforated or also unperforated. The first stamps were all unperforated. It was not until the 19s that the first perforated stamps appeared, which naturally made sales at post offices easier. Nevertheless, we still see many unperforated stamps afterwards. This may be the result of a strike in the printing industry, such as with the Netherlands in 1923; sometimes unperforated copies were given away to dignitaries. It is also possible that a part or a few copies remained unperforated by accident (sometimes even just one side). Usually, however, stamps were issued on the market unperforated under the guise of exclusivity, allowing a higher price to be charged to collectors.
A clear philatelic article. This leaves you wanting more.