Zachary Taylor 5c

Interesting. About all I can add to the puzzle is that this appears to be Scott 179. There is also 181, but it's $450,000 and fewer than 10 are known. #185 appears to be an imperf if I'm reading the catalog correctly. But I could not find anything as far as a different size reference.
I'd like to hear what one of the experts on here can point out.
brookbam

[EDIT: ignore this post, especially last paragraph, I looked at one of the pics incorrectly. Sorry.]

In this case, the physical size of the entire stamps has nothing to do with paper or plate differences -- simply positioning of the perforating wheel when the stamp was perforated after the printing was completed. Stamps back then were line perforated. So it would not be unusual to find variations in widths or heights when comparing columns/rows within the same sheet. Your "larger" stamp on the right would be a nice large margin example. But the foxing unfortunately works against any premium associated with the larger margins.

For the Banknotes, it's been documented that for some issues, the perforation variation was deliberate. The perimeter rows have a slowly but noticeably increasing wider margin on 1 or 2 sides.

If it was an issue of paper moisture, the dimensions of the stamp design would be affected, in either 1 or 2 directions. As shown the pics provided, the stamp design dimensions are the same in all directions.

OK, I see it. I was looking at your 1st pic and not paying attention to the bottom of the better 4th pic.

Therefore, I walk back my first post.

Left stamp is #179. Right stamp is #185. brookbam was on the right track. Both stamps are listed in the catalog as perf 12, including #185.

From the excellent back view pic held up to light, the paper can be identified as "normal" wove (#179) and soft porous paper (#185).

Regarding the difference in vertical design/paper height, the explanation is a little tricky. The pics you supplied are camera pics and not scans, so there is a slight angle and the stamps are not completely flat. You will need to physically verify my "observations" from the camera pics.

These were printed during the "wet" printing era. The original moisture content of the paper (15%-35%), although significantly higher than the much later "dry" printing era (5%-10%), still varied over a large range. This could "technically" produce an ever so slightly taller stamp design if the original paper moisture content was at the lower end, compared to a stamp produced with a higher end moisture content, even within the wet printing era. Your ruler is not graduated evenly. I would say the difference in stamp design height in your 2 stamps is much less than ½mm, closer to ¼mm.

Out of curiosity, I pulled some #179s and #185s, and lo and behold, I could find a maximum ¼mm different in stamp design height among the stamps! Coupled with no difference in widths! You will notice that Scott gives a "range" on some the rotary vs. flat plate measurements, rather than exact measurements. I've mentioned before, this is to accommodate typical production variation -- when you are comparing ¼mm differences, it wasn't intended to reproduce stamp dimensions that accurately back then. Hence, ranges in paper moisture specifications, paper thickness...

Now here are some "interesting" things. My earlier comments about variations in perforation spacing still holds correct. Even a ½mm difference in stamp dimension height won't produce a 1mm difference in paper height. Your physical stamp is larger primarily because of the perforation wheel positioning.

But, it appears that your vertical perforations on both stamps are not the same! Ever so slightly off! Or maybe it's the camera angle? Please line up the vertical perforations and see if they line up well, or are off by about 1/8 hole as you go from top to bottom. Perforation is done well after stamp is printed and dried, including after the any applied gum has dried. So it should be unaffected by paper shrinkage. On my 179/186s, the perfs all line up well, even if the stamp dimensions were off by 1/8-1/4mm.

If your vertical perfs line up well, then no issue. But if they don't align well (and I can tell your stamps have not been reperfed), then there aren't many other reasonable possibilities to explain why the perfs on the taller stamp are also stretched vertically...

In the past, there were some dealers who would use a press (either a full vertical press or a roller press) to squeeze out creases. Given that #186 is on the thicker soft porous paper, I wonder if someone in the distant past may have rolled the stamp vertically through a roller press. That would have caused a very small permanent deformation of the soft porous paper in the vertical direction and contributed to both the stamp design stretching and the perforation "stretching" in one direction.

As an aside, in previous decades, there used to be a company that advertised a full stamp press specifically for this purpose.

I guess I could also imagine a scenario involving blotting paper that might also produce such an effect, but would be unsure how much and if it were permanent.

At any rate, interesting stamp/observation on your part. I wouldn't have thought to pull out my stamps to compare had you not posted.