These stamps were issued in panes of 100 from sheets of 400. So the line at left and the left edge (known as a "natural straight edge) are the result of this stamp coming from the right pain of 100, either top or bottom, and you are seeing the center line that ran the full length of the sheet.
Collectors vary on their acceptance of natural straight edges in their collection which has also led to a lot of reperforations of various issues.
No. Joint lines are for coils, and come not only from the horizontal and vertical guidelines (in flat plates), but also from the roller line in rotary press coils, as the tumbler left a line at the seam, though the reason for the lines are different in flat plate vs. rotary coils, the term "joint line" is still used for coils, this is usually for two or more, in the case of a "Joint line pair" as mentioned in Scott for coils.
Hey George, just re-read that, and I read your comment wrong, and that makes my reply inaccurate as well.
Flat plate coil pairs are Guideline Pairs, while Rotary press coil pairs are Joint Line Pairs. As you rightly pointed out, "joint lines" in rotary presses, however these only appear in rotary press coils, and as mentioned their presence is created more as a by-product than a purposeful line that is used for anything, as was the case in flat plate prints.
This is an example of a rotary pane of 100.
And this a rotary pane of 170.
Note, the absence of either vertical or horizonal lines.
Yes, that's right George. The cylinders were two curved plates mounted to the rotary drum. Ink would buildup in the well they create. Unlike guide lines, they vary in thickness within even a single stamp, and sometimes can appear smeary.
Comments
Collectors vary on their acceptance of natural straight edges in their collection which has also led to a lot of reperforations of various issues.
Hope this adds clarity to my comment.
And is why you can have a "center line block of 4" in this issue, but not in the denominations of Franklin-Washington below $2.
Flat plate coil pairs are Guideline Pairs, while Rotary press coil pairs are Joint Line Pairs. As you rightly pointed out, "joint lines" in rotary presses, however these only appear in rotary press coils, and as mentioned their presence is created more as a by-product than a purposeful line that is used for anything, as was the case in flat plate prints.
This is an example of a rotary pane of 100.
And this a rotary pane of 170.
Note, the absence of either vertical or horizonal lines.