Perforation is the most common method of allowing stamps to be separated easily from a sheet without scissors. The world’s earliest stamps were imperforate, but Great Britain introduced the first perforated postage stamps in 1854. Knowing both the perforation gauge and the method of perforation is essential for identifying some stamp issues. The condition of the perforations also has a major effect on a stamp’s grade and value.

Methods of perforation

Harrows perforation: the perforating pins are arranged in both horizontal and vertical rows so that all four sides of each stamp position are perforated in a single operation. The corner perforations are therefore regular and uniform.

Line perforation: the pins are arranged in a single row, so the horizontal and vertical perforation lines of the sheet are made separately. Where the lines meet at the corners, the perforations may be irregular.

Comb perforation: in each stroke the perforating comb perforates three sides of a row of stamps; the remaining fourth side is completed by the next stroke. On the final stroke, the perforation may extend into the sheet margin. Corner perforations are as regular as those produced by harrows perforation, so the two methods can often be distinguished only on complete sheets.

A special form of comb perforation is cross-comb perforation. Here the perforating unit is shaped like a double comb, with perpendicular bars attached to both sides of the horizontal base. In Hungary it was first used on the 1955 Winter Sports issue and later on other stamps of the same size. The perpendicular sections carry 13 pins on one side and 6 on the other, producing a characteristic pattern in the sheet margin.

Until 1874, harrows perforation was used exclusively. It was then largely replaced by line perforation, while harrows perforation later remained in use mainly for souvenir sheets and some miniature sheets.

Line-perforating machines were used regularly between 1874 and 1904. On some comb-perforated Turul sheets, rows accidentally left imperforate were later completed by line perforation. After 1906, comb perforation was used almost exclusively, apart from a few exceptions. With line perforation, the same sheet was often perforated on two different machines, which could result in different gauges on the horizontal and vertical sides of the stamps.

Perforation gauge

Perforation gauge is expressed as the number of perforation holes or teeth occurring within a length of 20 millimetres. Measuring it is particularly important when the same stamp exists with more than one perforation gauge, as with many Krajcár and Turul issues.

If the horizontal and vertical sides of a stamp have different gauges, the stamp has compound perforation. Catalogues normally list the horizontal gauge first and the vertical gauge second, for example 12½ : 12. More than two different gauges on a single stamp are rare; when this occurs, the measurements are usually given clockwise beginning with the top side.

Perforations are measured with a perforation gauge, which may be made of paper, plastic or metal.

A perforation gauge carries a series of scales corresponding to different perforation measurements. The stamp is moved over the scales until the perforation holes align exactly with the markings. Stamp tongs should always be used when handling stamps for examination.

Condition of the perforations

The condition of the perforations has a major influence on a stamp’s market and collector value. A mint never hinged stamp can only be considered fully sound if all perforations are complete and undamaged. Even on used stamps, a single missing or damaged tooth may significantly reduce the value. Stamps should therefore be handled with particular care, especially when placing them in albums, because the perforations are among the most vulnerable parts of a stamp.

Perforation varieties

Conspicuous perforation errors arising during production can be important value-enhancing varieties. They may occur when the sheet shifts or becomes creased during perforation, or when the perforating machine is incorrectly adjusted.

Perforation through the design describes a major misplacement in which the perforation line cuts into the printed design. In such cases, part of the neighbouring stamp’s design may also be visible.

Related article: Perforation varieties.

Forged perforations

One form of philatelic fraud involves forged perforations. A classic example concerns the 1871 issues, where stamp designs cut from much cheaper stamped envelopes were perforated afterwards to imitate genuine lithographed or engraved stamps. The well-known Swiss stamp forger François Fournier (1846–1917) frequently used this method.

When a stamp was issued with several perforation gauges, the scarcer varieties may be worth considerably more than the common ones. This price difference can provide an incentive to alter or forge the perforations.

On complete stamp forgeries, of course, the perforations are counterfeit just like every other element of the stamp.

Opinions differ regarding reperforation and perforation repairs, such as replacing missing or damaged teeth. Some collectors regard such work as a form of falsification, while others see it as restoration or preservation. In every case, however, any repair or alteration should be clearly disclosed.