In order to list the different perfin dies it is necessary to list more than
just the perfin letters, as the perfin "B&Co" demonstrates well,
the above being just a small selection.
All known perfins on GB stamps are allocated a Perfin Society catalogue number. These catalogue numbers are used throughout the Society's publications. Clearly a life size illustration is the easiest way to describe a perfin, but a system for describing perfins using only text has been developed:
Firstly a forward slash is used to denote a new line in the perfin. So in the examples shown above, the die on the far left is B&Co, but the far right die is B/&/Co.
Then the height of the letters in millimetres is measured (ignoring the small o in Co).
The next step is to record the number of pins (holes) that make up each individual
letter. For instance, the middle die above has 11 holes making up the B, 12 in the &, 7 in the C and 4 in the o.
This gives a pin count of 11/12,7,4.
The final step is to examine the shape of the ampersand '&' character that frequently
appears in perfin designs. The classification system for ampersands is detailed in the Society's "Tomkins" catalogue.
Using these properties it is possible to uniquely identify the majority
of perfins. This is the system used in the Tomkins catalogue of identified perfins.
However there are a number of perfin dies where differences may
be quite subtle, giving the same description based on the rules above but being sufficiently different to warrant different catalogue numbers. In these cases it is best to compare against example illustrations as used in the New Illustrated catalogue. On the left is an example of two perfins that are so similar they have the same text description.
Although it may still seem difficult to see the differences in the illustrations, laying a perfinned stamp over the illustrations in the catalogue and trying to get the holes to line up usually separates the different dies very quickly.
The orientation of the perfin on the stamp (upright, sideways, inverted) is not used in the classification.