What is a PNC?
Even some U.S. stamp collectors are stumped when they encounter those unfamiliar initials in print.
Many collectors know, however, that PNC stands for "plate number coil." Those initials refer to a fascinating aspect of the stamp hobby that has been in existence for a mere 17 years.
Let's define a couple of terms before we proceed much further.
Coil stamps are specially manufactured and processed as one long continuous strip. They are wound — or coiled — into a tight little roll and packaged for sale.
Often you may see coil stamps dispensed from coin-operated machines in post office lobbies.
Most modern U.S. coil stamps can be identified by their straight edges. Two parallel sides of a coil stamp have straight edges, while the other two sides have perforation holes.
The term "plate number" refers to numerals (and sometimes letters) that identify the printing plate used to print a specific stamp.
Actually, the majority of U.S. stamps now have their designs printed by cylinders rather than plates, but the term "plate number" is still used more often than the more technically accurate "cylinder number."
When you put it all together, you find that plate number coils are coil stamps that have the plate or cylinder number printed as part of the design of the stamp.
Since the first PNC was created in 1981, the number has always appeared at specific intervals in the coil, not on every single stamp.
Often the interval is every 24th or 48th stamp for issues printed by the U.S. Bureau of Engraving and Printing.
The interval numbers have ranged from as few as seven to as many as 52.
Look at the two 18¢ Surrey coil stamps shown in Figure 1. The stamp at left has a small number "6" printed near the bottom of the stamp. The stamp at the right does not.
Coil stamps from the Transportation series, such as the Surrey stamp, were all printed with plate numbers at regular intervals.
The first coil stamp with plate numbers was the 18¢ Flag coil issued April 24, 1981. A tiny digit was printed on the bottom of every 52nd stamp.
Plate number coil collecting grew in popularity as collectors realized that different numbers were used when a new cylinder was installed to print the stamps.
Collectors of mint stamps had some problems deciding the best way to save the new stamps. Previous coil stamps would show a joint line printed vertically between two stamps at certain intervals, and collectors were used to saving a pair of stamps with the line between them.
If you look again at Figure 1, you can see that some of the early PNCs were also printed with a joint line. The plate number always appeared on the last stamp along the joint (gap) between the two curved plates. Ink build-up in the gap between the plates created the printed joint line.
After a while most collectors of mint stamps decided that strips of five, with the plate number appearing on the center stamp, was a suitable format to collect. Some save strips of three.
Some specialist collectors have chosen to save longer mint strips, depending upon the issue.
For collectors of postally used stamps, plate number coil collecting became a substantial challenge.
Out of all the many mail pieces that are franked with coil stamps, remember, only one of 24 or so will bear a stamp that has a plate number upon it.
Because of this scarcity factor, some collectors prefer to save postally used PNCs "on cover." Rather than clipping the stamp from the envelope and soaking it off, the collector keeps the entire envelope. This shows how the stamp was used as well as the date and location of mailing as revealed by the postmark.
Take for example the $1 Seaplane coil stamp shown on cover in Figure 2.
If it were soaked off cover, the plate number single would make a fine addition to a collection of used stamps.
Left intact on the cover, though, a history of the stamp emerges. It was used to mail a letter from Toledo, Ohio, to Germany in 1996. Then, as now, the airmail rate to Europe for a letter weighing 1/2 ounce to 1 ounce was exactly $1, so the stamp precisely paid the proper postage.
Cylinder numbers are still printed on the newest coil stamps, including the Wetlands and Diner nondenominated stamps issued June 5. Plate number strips of five of each are shown in Figure 3.
These multicolor stamps have multicolor cylinder numbers: each digit is a different color, corresponding to the different gravure cylinders used to print each color.
While lick-and-stick style stamps are easily separated, collectors encountered another puzzle when newer self-adhesive coils emerged.
Early self-adhesive coils were printed on long strips of backing paper and each stamp was spaced a few millimeters away from its neighbor. Collectors could easily cut between two stamps to save whatever size strip was desired.
A new process of interlocking wavy-line die cuts made things a little trickier. Any attempt at cutting strips apart meant a stamp would be cut as well.
To avoid doing that, collectors learned to prepare the strips before cutting.
The process is shown in sequence in Figure 4. A full coil of 100 20¢ Blue Jay stamps, for example, comes in a plastic bubble-pack container. When the pack is opened, the collector can find a plate number by looking closely at the bottoms of the stamps.
In the center photo, the collector peels off a stamp from either side of the desired strip of five. The removed stamps can be saved for later postage use by placing them on an empty self-adhesive booklet backing or similar material.
With the two stamps removed, the collector carefully cuts through the vacated liner paper to create the strip of five self-adhesive stamps shown at the bottom of the illustration.
Again, the tiny cylinder numbers are located on the center stamp of the strip.
The Plate Number Coil Collectors Club provides regular news and features about the PNC specialty through its monthly journal Coil Line. Included are frequent updates on new collector and dealer discoveries.
For additional information, send an addressed, stamped envelope to club secretary Gene Trinks, 3603 Bellows Court, Troy, MI 48083.