Understanding Examples For Flat Vs. Rotary Printing Quality

Hello,

I know that there are these 2 mentioned printing methods and that you can see differences like color and printing quality. Though I still didn't find an example like the one I attach here. I found here in the forum and in the internet the information that rotary is a brighter green and has finer lines. But to be sure I understood this correctly: Between the following three examples, is the first rotary, second flat, but the third one? The lines are finer than at other flat stamps, the printing is quite good, but the color is like flat. Can an expert see from this photo if it's flat or rotary? I don't mention the perforation and so on because I really want to learn this from the printing quality perspective.
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Added: About the "quality" I am confused as I read different things, once: "flat is sharper" (but lines are less fine?), once: "rotary has higher quality" (because of fine lines) and so on. So is printing quality the parameter, and which quality exactly, or are the fine lines the parameter?

Not sure if you have seen this page
http://www.stampsmarter.com/learnin...methods.html
Don

Yes, Don, I know these helpful articles on stampsmarter. But there is only mentioned size and setoff as difference. My topic here should be only about printing quality, as I read many times now that there is a difference in printing between rotary and flat (color, fine lines), but I can't get it together into one picture of knowledge. That's why I gave these three examples to learn if you can see flat vs. rotary while looking at printing layout and quality.

This is from the link supplied above...



Don

thank you again :), but I don't search the difference between offset and flat/rotary but between flat and rotary, and this concerning the printing image.

Ah, I see.
Don

For the most part, both were intaglio (recess line engraved) printed and printed on wet paper which was dried and gummed after printing. Some say that the quality of printing is better on flat or rotary than on rotary or flat but it may all depend on each individual stamp itself.

Would it be more accurate to say that the offset process does not involve direct contact of paper with an engraved plate? I'm not aware that the offset process necessarily excludes the use of an engraved plate as a source of transferring ink to a rubber blanket which then contacts the stamp paper. Lithographed limestone plates first were used in discovering and developing the process outside of stamp production, and photo-preparation of soft metal plates later was used, but I don't think there is any reason that an engraved plate couldn't be used, it's just more costly and doesn't yield an advantage.

Chris

I was able to place a piece of alum foil and by gently rubbing the design will show if it intaglio.

All this is interesting, but to come back to rotary vs. flat: I really thought that it would be easy to say which printing method my three examples are, but as it seems now here in the forum, it's not. I read the things concerning brighter green and finer lines for rotary, but wasn't sure if this was a real determinating reason for or against rotary. I found good information here:
http://goscf.com/t/40718&whichpage=1

So getting back to my three images I would still say:
first stamp is rotary
second stamp is flat

So I am right now if I think that also an expert can't say if the third stamp is flat or rotary only by looking at the printing quality? If so, I would then know this and go to the next step for ID, meaning perf or size.

As has been said, the rotary press and flat plate images may be slightly different sizes, and the perforations may also help in identification.

Inking and printing quality can vary because of many factors, including viscosity, temperature, ink color, plate wear, and plate wiping to name a few. I cannot say if there is any innate quality difference between rotary press and flat plate printing since all of my intaglio printing experience is with flat plates.

One would assume that the plates themselves were of a very similar if not identical quality.

Hello and thank you. So even the thing with the fine or not too fine lines and details is not really a factor if I want to see a printing difference between flat and rotary? I just ask as this was mentioned at least twice here in the forum (also in the link I gave above). And in general I can imagine that there are differences although the plates are similar because it's just a different printing method.

The examples you show in this thread are from the 4th Bureau issue. The 1¢ Franklin you can tell by color, flat plate is a darker green and the Rotary press is yellow green. The 2¢ Washington to me isn't that easy. They are both listed as Carmine.


Flat plate Scott 554






Rotary press Scott 634







To my eye I don't see that much of a difference in this particular stamp. Easy way to tell on these is the Flat plate are perf 11 and rotary is 11 x 10½. For me the easiest way to tell the difference between Flat plate and rotary press is actually by looking at the back of the stamp. Flat plate stamps will usually have a setoff (Ink on the back of the stamp) from stacking the sheets before the ink was completely dry. You usually will not see this on rotary press stamps.


Flat plate





Rotary press





When dealing with the Washington / Franklin series I think it is much easier to tell flat plate from rotary press and offset printing has a look of it's own. But nonetheless, I still look at the back first to see if it's a flat plate.

It may be futile to attempt to described the printing differences between flat plate and rotary press stamps to beginners or even intermediate collectors. This may be why the Scott Catalog starts with perforations as the defining difference. Continuous technological improvements to the Stickney rotary presses created a moving target as printing characteristics improved during each decade of use.

Initially, getting enough ink on rotary press plates resulted in "ink wash" affecting printings from 1915 to about 1925. Compare the Harding rotary press stamps compared to the higher contrast flat plate printings. The rotary press stamps look grayish in comparison because ink wash lowers the contrast between unprinted paper and the design. Similar problems existed with the Washington/Franklin rotary press stamps and the perf 10 Bureau issues. Better printing results allowed brighter and lighter colors starting sometime after 1930.

An experienced dealer or collector should be able identify most rotary press stamps by their appearance. First, and most important is the aspect ratio. Rotary press coils are significantly wider and sheet stamps significantly taller. Flat plate stamps have a squat appearance compared to rotary press sheet stamps. Flat plate booklet pane singles look almost square compared to flat plate sheet stamps. In many cases the color is sufficient. The 1 cent flat plate stamp is a much deeper and richer green. Both it and the 2 cent have less unprinted area because engraved lines in the design are less well defined and look wider because some ink will be squeezed from the recesses of the plate because of the intense pressure of the roller to force contact between the damp sheet of paper and the flat plate press. Rotary press stamps were printed on somewhat dryer paper. Other denominations have markedly different flat plate and rotary press shades. Rotary press shades morphed to rather dull looking colors to brighter shades after 1930.

Finally, the top and bottom perforations of rotary sheet stamps are aligned between rows while flat plate perforations are randomly misaligned between rows. Rotary press coils have aligned perforations while flat plate coils do not. Also, rotary press sheet stamps generally have gum breakers and coils may show a gum skip or streak running in the direction of the coil.

All of these differences mean that only a very few stamps require more thorough examination.

Well..., that's a SCF Hall of Fame worthy response.

Thank you both for the helpful answers. Clark, indeed you are a good explainer and should think about writing a book for introduction into US classic stamps. Or also just continue helping people here at SCF :).

Let me now "zoom out" and show you the third stamp from my initial post above again. Even now after I read all the answers here, this stamp still confuses me:
- color: flat
- perforation 11: flat
- perforation aligned: rotary
- size (a bit larger): rotary
- no ink setoff: rotary
- ink wash around letters: rotary
- straight edge: rotary/flat?
- overall printing quality: rotary/flat?

You see, that's why I asked about the printing quality :). What would I do now to see if it's rotary or flat? Can you see the difference from the zoom to the letters? There seems to be ink around and also inside the letters. (don't look at the color of the letters photos, the color of the total scan is correct)

thank you again.