Hey Robert,
"Measuring" perforations isn't exactly measuring. You're actually gauging them to the closest known size. Things like paper shrinkage means that you'll often come across measurements that aren't what you expect. Also, the perforations are slightly different between flat plate and rotary prints. Further confusing the situation is that you might get lucky and come across a rotary waste stamp that has a combination of flat plate and rotary perforations. A sure method is to look at two characteristics, rough perforation measurement and design size.
Pick your ugliest 11 x 10.5 stamp and cut the corners off as shown in the following link. You could also use a non-coil stamp from the 1938 Presidential series. They are all "Tall" rotary prints with the same design size.
http://www.kenmorestamp.com/flat-vs-rotaryLaying the template over an unidentified stamp as shown in the link will tell you if it is rotary or not.
- If the unknown stamp is the same height, then it is a "Tall" rotary.
- If the unknown stamp is wider, then it is a "Wide" rotary.
- If the unknown stamp is shorter and the same width, then it is a flat plate or offset printing.
Note that there are no offset printings for the 1922 series. Only the Washingtons from the previous series can be offset. They are actually a bit smaller than flat plate stamps.
The design sizes of the Washington/Franklins, 1922, and 1938 series are the same for each of the 3 main printing types. However, the 1922 "Wide" prints are slightly wider than the W/F. Regardless, the test using a template still works for all of them.
Okay, you now know if your unknown stamp is rotary or not and have a rough perforation gauging. Next look through the 1847USA site and find the Scott # that it matches. Post scans of any that don't neatly fit into a #. Post scans if you want us to double check your work. It takes a bit of practice, but you'll get the hang of it soon. Good luck!
Posted 10/16/2015 09:19 am
