The rotary press printing method provided many advantages in the manufacture of U.S. postage stamps, primarily in the speed of production allowing the printing of stamps on rolls of paper rather than on the single sheet at a time of the flat plate method. It also allowed the gumming of stamps as a roll rather than by the individual sheet, again a big time-saver. 

However, when the rotary press rolls were cut down to sheets to be delivered to post offices, the sheets tended to curl back into their rolled form. This was not a problem with rotary coils which were sold in rolls, but it was a problem for postal clerks who needed the sheets of stamps to lie flat in their drawers. More pressing was the fact that it was exceptionally difficult to add pre-cancels to the curled sheets without tearing the sheets apart at the perforations, a problem that was alleviated somewhat as the Bureau took over the pre-canceling chore. 

Since un-gummed sheets from the rotary rolls did not curl, it was noted that the gum must be the cause of the curling. By simply adding "breaks" in the gum the curling was reduced considerably. 

The three¹ main types of gum breakers and the numbering system as described by Armstrong are shown in the diagram below.

Type I Gum Breaker 1923(?)-19282	Type II Gum Breaker 1928-19302	Type III Gum Breaker 1930-1960's2
The spacing between the Type I breaker bars is 5.5 mm, allowing between 4 to 5 bars per stamp. This type of gum breaker was used on definitive stamps from possibly as early as 1923 until the end of 1928. The Type II breakers were first introduced in March 1928 to offset the "corrugated" look and feel of the Type I breakers.	The spacing between the Type II horizontal breaker bars is 22 mm, allowing only one bar per stamp, unless the bars are at the very top and bottom of the stamp, in which case there may be two bars. Note the 14 vertical ridges; all Type II stamps must have these ridges.	The spacing between the Type III breaker bars is 12 mm, allowing between 2 to 3 bars per stamp. The gum on these stamps is slightly glossier and smoother than the gum on the previous types. The Type III  breaker wasn't introduced until 1930, which means it can never appear on the Kansas-Nebraska or Hawaii overprints of 1928-29.

The different breaker types are the result of experiments by the Bureau and the Bureau's Benjamin Stickney to perfect the original gum breaker roll device. There were other experimental breaker types and use of ridges¹, but these three are found on the majority of stamps with gum breakers. 

The original breakers, the Type I breakers, gave the stamps a corrugated look and feel. In fact, the Type I "breaks" are often so pronounced the editor has occasionally seen lingering evidence of the breaker bars on used stamps without any gum. Types II and III, among others, were refinements aimed at reducing this, with the Type III breaker ultimately winning out and remaining in use until the 1960's. 

The first stamps with the Type I breakers were the rotary perf 10 stamps, Scott's 581-591. Early printings of the one and two³ cents stamps did not have the gum breakers. These stamps are much scarcer than their later counterparts with breakers and bring a premium.

Type I gum breakers are not common on the perf 11 x 10.5 rotary definitives of 1927-1938, Scott's 632-642. Although not rare, they are scarce enough to command a premium over stamps with Types II and III breakers. 

The importance of the gum breakers can not be overstated in the study of the overprints of 1928 and 1929. All Kansas-Nebraska, as well as the Molly Pitcher and Hawaii overprints, must have Type II gum breakers. If the stamp has gum and it does not show the type II gum breakers, it is simply not genuine. For this reason, many collectors refuse to collect the overprints without gum. There are other ways to verify the overprints, but gum breaker type is certainly important. 

¹ There are many experimental gum breaker types other than the three noted here. In the 1948 issue of The Bureau Specialist, Durland writes, "I have before me nine different breaker varieties on that stamp alone (Scott 634 - ed.) , and they were taken from a comparatively small number of blocks." Sloane wrote about a block of the twenty cent Special Delivery stamp with breakers running in both directions. 

² There is some confusion  as to when the various gum breakers were in use. This editor has found a perf 10, Scott 581, with what appear to be something quite similar to Type III gum breakers. We have used Johl, Micarelli and Armstrong (see below) as the source of the information contained on this page, and this does not seem to fit with what they report.

Because the Kansas Nebraska overprints were printed over a short run, it is reasonable to assume that they were all gummed with the Type II breakers, important for authentication purposes. Micarelli states that the rotary perf 10's (Scott's 581-591) were gummed with Type I breakers, with early printings of  the one and one and a half cent stamp gummed with no breakers, that the perf 11 x 10.5 rotary stamps  (Scott's 632-642) were gummed with all three types of breakers, and that the higher denomination rotary stamps (Scott's 692-701) were all gummed with Type III breakers.

³ Both Armstrong and Micarelli report that the early printings of the one and one-half cent rotary stamp were issued without breakers. We find this unlikely, since the two cent experimental rotary perf 10 stamp (Scott 583) was issued in the spring of 1924, while the one and one-half cent stamp (Scott 582) was not issued until 1925, making the two cent stamp a more likely candidate to be found without gum breakers. We were able to locate one and two cent stamps without breakers, but were unable to locate a one and one-half cent stamp without. If the reader has information regarding this we would appreciate your input: email 1847USA 


For more information we recommend the following references:

US Definitive Series 1922-1938 by Martin A. Armstrong - Trenton Publishing Co, 1980

The Micarelli Identification Guide to United States Stamps by Charles N. Micarelli - Scott Publishing Co., 1991

United States Postage Stamps 1902-1935 by Max G, Johl - Quarterman Publications, Inc., 1976