From Clark (concerning the horizontals): "A perf 11 stamp will have 11 holes and 10 tips or 11 tips and 10 complete holes between the lines." This can be used to identify perf 10 and 12 by counting above or below the numbers quoted for perf 11. I count 11 holes and just above 10 tips on this stamp.
Often times looking at the vertical is necessary and/or can help determining perfs. This is obviously a flat plate print, isn't 10x12 nor the 12x10 possibility, so the vertical perfs should be the same as the horizontal (only applies to certain series such as this flat plate print 1c 1908 series Washington).
I count 13 complete holes and a small portion of one tip on the left vertical side. Perf 10 will have approximately 11 complete holes, perf 11 =~ 12 holes, and perf 12 =~ 13 holes
I scaled a known perf 12 to the same design size to get this comparison. Note that paper can shrink or a printing can be larger than others, but comparing whole number perf differences is pretty easy to see:
Last Edit: Note that you can only use this image scaling method with stamps that have the same design size. Doing it with flat plate stamps is almost always safe. It gets trickier with rotaries and offset printings. Also, this will not work with booklet compared to non-booklet stamps. It also won't work for comparing AEF booklet to normal booklet stamps. Your results on non-flat plate prints can be useful, but need to be done while considering more factors.
Posted 11/29/2014 9:40 pm
