Quote:
...this likely Scott 68, which I nicknamed Abe Washington
I actually laughed out loud reading that!
To piggyback on what Zebra wrote on the previous page, the line indicates where the full sheet was divded into two panes. Note the vertical line in your stamp:
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Now have a look at this image, from the original 1951 Harmer sale photographs of a full pane of 200. This excerpt is of the upper RH quadrant of the left pane of stamps.
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The line you see was engraved into the plate (two panes of 100) indicating where the full sheet of 200 was to be divided. There is a similar line at the bottom of the plate, not illustrated.
Now, that photo excerpt is of a printing from Plate 4, the Type I design of the 10c, of which only a relatively small number were printed. Your stamp is Type II (Scott 68), printed either from Plate 15 or 26. Though I'm not aware of photos of fulls sheet of either of those plates, there exist examples of Type II stamps printed from those plates which exhibit the same line, and all have straight edges on either the left or the right.
• If the straight edge and line occurs on the left, that's position 1 from the right pane
• If the straight edge and line occurs on the right, that's position 10 from the left pane
At the end of the day, what you're looking at in your stamp is an example from a miscut pane.
[Edited to add the following image and info]
From the 2023 Siegel Sale of the Gilbart collection, here's a similar example, opposite positioning. Sale 1292, Lot 25, Scott #68, described as a straddle pane example that straddles the left pane.
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