What Size Is A Plate Block?

By Rick Burdsall

Why do some issues call for a plate block to be something other than 4 stamps?

The definition of a proper "plate block" really hinges (sorry about the pun) on the printing method used to produce the stamps.

In the early days, stamps were produced by flat plate printings. Plate numbers appeared at the top center, bottom center and L and R center of the sheets. If you wanted to save an aesthetically pleasing and balanced block of the stamps, then you needed the one next to the plate number, obviously; plus one on each side for balance; and then one "deep" into the sheet of stamps — in other words, a plate block of 6 stamps. On some issues, in addition to the number, you had a bureau imprint or other markings, and it might take 8 stamps to make a balanced plate block.

This continued from the Banknotes (1870s) through the 1920s. The Post Office was experimenting with producing stamps faster, and the flat plate method, one sheet at a time, was frankly too slow. The Rotary Press allowed the stamps to be produced from a web of paper, more or less constantly. The rotary press had the plate numbers in the corners of the sheets, which when trimmed meant they were in the corners of the panes of 100 (or 50). No longer were there two plate numbers on each pane, but now only one. For balance, you only needed four stamps — the corner one adjacent to the plate number; plus one each horizontally and vertically; plus one deep. Rotary press stamps produced billions of stamps cheaply and quickly for hundreds of issues from the 1920s through the 1970s.

The rotary presses only produced stamps in a single color. The Post Office wanted to produce more attractive stamps with more color and variety. In the early 1960s new presses were available that would allow simultaneous printing of more than one color, but they were initially slow and expensive. Later in the decade, separate rotary presses were made for each color. The Post Office decided that each color required a separate plate number. Since plate numbers had been assigned sequentially since 1894 and were now up to five digits each, it was impossible to fit all those plate numbers adjacent to a single stamp. So they started spreading them out, with one in the corner and adding each additional color on an adjacent stamp. This meant that to save a "plate block" you needed all the stamps with numbers, plus one deep. If the stamp was printed in four colors, then you needed a plate block of 8; if in six colors, a plate block of 12.

On some of the presses, the numbers "floated" — the printing was not in round numbers of 10 as the individual panes were trimmed and sold (panes of 50 or 100 stamps) — so the six colors of plate numbers might not be adjacent to each other and could be mixed in with other marginal markings — Mail Early, Use ZIP Code, the Copyright notice and so on. So you might have to save a full strip of 20 stamps — nearly half the post office pane — to save a "proper" plate strip (now no longer a plate block).

Plate block collecting was becoming very expensive from the late 1960s through the 1970s. Collectors were leaving the hobby in droves, either collecting only issues up to a certain date, or giving up altogether. The way the plate blocks were produced nearly killed that aspect of the hobby.

Two things happened in 1981 that discontinued the practice and revived the hobby. One was the addition of private printers to the mix. The Bureau of Engraving and Printing had produced virtually all stamps for the Post Office since 1894. Private security printers wanted a chance at some of that business and when it was opened up for bidding, proved to be very competitive. Since they couldn't assign a BEP five-digit sequential plate number to a stamp produced by a private company, they hit upon using a prefix letter to represent each company (A for American Bank Note Company, V for Avery-Dennison, etc.), and followed that by a "representative" plate number for each color. Generally, 1 was used first, so you would end up with A1111 if four colors were used, with each 1 a different color and representing a different actual plate number. If the printer changed plates for, say, green during the printing, then the number might be A1121 if the third number was green. BEP was still producing stamps through this period and adopted the same policy; however, BEP-produced stamps have no letter prefix. 11111 would be the initial plate number for a five-color stamp produced by BEP.

So, these plate numbers would now fit on a single stamp in the corner, and we were back to plate blocks of 4 again, for the most part. (Some stamps were still produced on the printers which floated, but at least those would appear on the side or top and could be collected as a plate block of 6 — rather than 12 or 20.)

At the same time, they started putting plate numbers on the face of coil stamps. The extremely attractive and popular Transportation Coils did more to revive plate number collecting than any other single act, in my opinion.

Everything was great for 20 years or so. BEP could no longer compete with the private companies, only producing high-volume coil stamps for its final five years or so. Most recently someone at USPS decided the different plate numbers were no longer necessary for internal accounting purposes and decreed essentially that only plate number 1 would ever be used, with some rare exceptions. Once again the postal agency is killing this aspect of the hobby, this time through an ill-advised and probably non-existent attempt at savings (see Robert Rabinowitz's opinion column in Linn's Stamp News, Sept. 4) rather than through the previous practice of making the practice unaffordable for many collectors. Some plate block collectors will stop with 2005, or 2000, or give up altogether; others will muddle along trying to make do with the current practice and hope to overturn it, or that new management will correct the practice.

So, in your specific example, you asked about the Gershwin / Tanner / Cather / Jeffers stamps (Sc. 1484-7). Since they were all produced using six colors of ink, and there are six adjacent five-digit plate numbers in the selvage (blank edge) of the panes of stamps, you need 12 stamps to make a proper plate block. The Scott catalog identifies the number of stamps making a generally-accepted or -agreed plate block.

You can find the same numbers in Upper Left, Upper Right, Lower Left and Lower Right positions for each of those stamps, making up what are called Complete Matched Sets for those numbers. However, each number is unique to each stamp — you won't find the yellow plate number on the Gershwin stamp also used for the yellow on the Robinson Jeffers stamp, for example. (There is one exception, where a single plate was used to produce four different stamp designs — but you'll only find Lower Left plate numbers for one issue, and Upper Left for the next and so on. These are all 20¢ issues from the early 1980s.)

There's a ton of information published on plate numbers and printing practices. The web site of the American Plate Number Single Society has some of the history and a list of private prefixes. Probably the best single source is the Encyclopedia of United States Stamps and Stamp Collecting, published last year by the United States Stamp Society. Individual authors provided chapters on their specialty areas, such as printing practices, plate numbers, marginal markings, different issues or series and so on, with a team of editors ensuring that each chapter was compatible with the others. During its brief availability it has outsold every stamp publication except one, and is now headed for a second printing. Get this book; you won't be sorry.

Another excellent reference is the Durland Standard Plate Number Catalog.