7¢ Grey black, black, intense black
Subject: George Washington
Printing Method: Flat Plate (see below)
Scott #: 507
Issued: March 24th, 1917
No postmark with gum (MH)
$2 - $5
Full perfect gum, no postmark
no trace of stamp hinge mark (MNH)
$12 - $19
#507 was issued with the following plate #'s
Perf 10 at top
The old 10 perforation stamps tore frequently when separated for sale at the post office counter. Experiments with 11 perforated stamps found the problem was largely cured. It was not until 1917 the change was made as the bureau wished to wear out the 10 perforation wheels before making the change.
As the curved plates of the Rotary press made the stamps slightly larger it is relatively easy to discern which stamp is flat plate and which is a rotary press stamp. First select any perf Washington Franklin stamp or the first issue Washington Franklin 1 cent or 2 cent. These are the stamps with the numbers one and two spelt out, instead of numbers being displayed. I chose the latter alternative as shown in the first image above.
Then cut out squares at each corner. As shown in the second image above. Placing the stamp you wish to test under your cut out stamp you can see if the frame lines match. If, as in the last image shown above the frame lines are outside the top stamp in either the top, bottom or sides then you have a rotary stamp. If the lines are in the same place, as shown in the third image, you have a flat plate stamp.
This test works with any value stamp.
The image above left is a perfect example of the reverse of a flat plate stamp. The flecks of ink on the reverse can be found on flat plate stamps and are rare on rotary press stamps. The cause of the flecks of ink is that during the flat plate process the sheets were placed on top of each other before the ink had a chance to dry properly.