Correctly Measuring Perforations

Perforations are one attribute of stamps that are quite often identified incorrectly. There are several reasons for this:

  1. Most catalogues quote perforation measurements to the nearest half, when the actual perforations are not exactly equal to the quoted number. Most cheaper metal, plastic or cardboard perforation gauges are only accurate the the nearest half perforation as well. 
  2. Most collectors therefore become accustomed to matching the stamp they have to the closest number they can on their perforation gauge and then choosing from the catalogue listings, which stamp they have. Generally, the differences between catalogue listings are so significant that it isn't necessary to learn to use an accurate perforation gauge correctly, so that many collectors are unfamiliar with the correct use of an Instanta gauge when they encounter one. 
  3. Most catalogues do not distinguish between comb and line perforations. 
  4. While the catalogue listings generally suffice to identify the basic printings of a set, there are often scarce printings whose perforation differs by one quarter of a hole or less, or it has the same measurement, but is comb rather than line, or vice versa. 
  5. Thus, in order to avoid overlooking better printings of many stamps, it becomes important to obtain an Instanta perforation gauge, and to know how to use it properly. 

What Is an Instanta Gauge?

The picture below shows my Instanta gauge that I use:

As you can see. it is a clear plastic gauge that has the perforation in halves along the left side and decimal graduations on the right. It can thus measure accurately to the nearest tenth of a hole, and with reasonable accuracy to the nearest 20th. 

You will see along the left side, there is a notation at the top that says "Guide Line". In order to measure perforations accurately, you must ensure that this line passes exactly through the middle of two opposing perforation teeth: one at the top of the stamp, and one at the bottom, or one on each side, if you are measuring the side perforations. It does not matter if you choose the first perforation tooth on a side, or the third, as long as you ensure that your guide line is straight. If it isn't, then your reading will not be accurate. 

It is for this reason, that I generally recommend placing the stamp to be measured in a clear protective stock card, and placing this on a flat surface, and the gauge on top. Some very experienced philatelists can hold the stock card in their hands and move the gauge with their thumb and index finger, but it is very easy to obtain inaccurate readings this way if you are not careful. 

The perforation measurement is obtained when, by sliding the gauge up or down, each slanted line on the gauge intersects a perforation tooth exactly in the middle, all the way along the gauge, including the very last line. A common mistake is to see most of the lines intersect perfectly and then assume you are done. You aren't. You have to make sure that each line intersects a tooth exactly in the middle. 

The following two pictures show the correct use and incorrect use of this gauge to measure the perforations on a 1935 Silver Jubilee stamp from St. Christopher and Nevis:

Here we have the correct use of the gauge. Note how the guide line at the left passes straight through the middle of a perforation tooth at the top left of the stamp and again at the bottom left. Then the slanting lines pass exactly through the middle of the top perforation teeth, which is the side we are measuring. If you look across at the numbers on the right, you can see that the actual perforation is 11.1. Gibbons lists this stamp as being perf. 11, but in reality, it is 11.1. 

Here we have an inaccurate reading of 11. Note how the lines align perfectly through the middle of the teeth until you reach the fifth perforation from the right, and then they are all slightly off. 

Mixed Perforations

Occasionally you will encounter situations where no matter which direction you slide the gauge, you cannot get a perfectly accurate reading. What this usually means is that two different gauges have been used to perforate the stamp, either because the spacing of the pins is not even, or because two different machines were used to complete the perforating, often due to a breakdown. This is where it becomes interesting to specialists. To obtain an accurate reading in these situations, you should measure up to the point where the last perfect alignment occurs, and then reposition the guide line through the two opposing perforation teeth at this spot. Repeat the process until you obtain an accurate reading for the rest of the teeth on that edge. 

Line Versus Comb Perforations

On many British Commonwealth issues the distinction between line and comb perforations becomes important where both exist, and one is scarcer than the other. 

The picture below shows an example of each type:

The stamp on the left is an example of a comb perforation. Comb perforations are done using perforating combs in which the pins are already laid out in a comb pattern and then applied to the sheet with a guillotine motion. The result is that the corner perforations are always perfectly even, so that if you place one stamp on top of another identical stamp, they will both line up perfectly on all 4 sides. 

The stamp on the right is an example of a line perforation. In the case of a line perforation, each column and row of the sheet is perforated separately by a wheel on which the perforating pins have been arranged. The result is that where corners meet in a sheet, there is often double punching of holes, or irregular punching. Consequenty, the corner perforations are always uneven, and if you place two identical stamps on top of one another, they will not align perfectly. 

Hopefully, this information should allow you to correctly identify and measure nearly all perforations you check. The key is not to rush it. Accurate measuring takes time. So it is generally not recommended to measure 100 stamps back to back in one sitting, as you will inevitably wind up with some inaccurate readings.