5c Zachary Taylor - Is This An Inking Error?

Came across this odd example of a 179/185 (which one not a question at this point) with a real lack of detail (the stamp on the left). I included a normal version to its right for comparison.



I then ran it through Retroreveal which also reflect the same missing detail.



There seems to be a real lack of vertical lines on all four corners and on the left edge of the stamp.

Is this just an under inked stamp or what?

It's not all that odd. This is due to printing plate wear, very strong in this case. You'll see this in the later 10c Banknotes a lot, also.

Caper123

Inking issues with this stamp seem to be common based on copies I've seen. Just two examples:

They used these plates to death; very worn examples are common.

Interesting tho how only the vertical lines were affected. Wherever they intersected with horizontal lines they remained intact as did the horizontal lines.

Most of the horizontal lines were cut deeper.

The problem on your stamp is not just about inking. It has as much to do with the paper moisture. For intaglio printing the usual procedure was to thoroughly moisten the paper stock (wet down) prior to printing, which allowed the paper to soften a bit and better conform to the recesses in the design on the plate. If the paper was not sufficiently moistened, or had dried too long before printing, the resulting "dry print" had shallow line detail and often had missed areas such as yours has on the left. It is a collectable variation though not separately cataloged.