Trivial Question About How Bi-Color US Stamps Were Printed (Circa 1900)

I understand that for intaglio printing, the paper is dampened before going under the printing plate, to make the ink adhere better. But in drying, paper typically curls (see here https://www.shorpy.com/node/24781, for instance; of course the stamps in the linked pic are gummed, which contributes to more curling). So for printing bi-color stamps in the early 20th century (Pan Am's, 294-299, e.g.), how did they do that? Surely they did not print both colors during a single wetting of the paper; the ink from the first color would have transferred to the plate for the second. Did they actually wet the paper two separate times with a drying cycle in between? If so, how did they deal with the curling from the first wetting/drying cycle? Or were they printed on dry paper?

Thank you.

*** Moved by Staff to a more appropriate forum. ***

FYI. At lunch the other week, I was shown a two color Bank Note company engraving which was printed in a single pass. Apparently and if I understood correctly, the two plates were nested inside each other and were then presented together during the printing pass. But I do not think this was common.
Don

In the case of the Pan-American Exposition series, the Smithsonian has full sheets of the frames, and full sheets of the centers. So I'm 99% sure those were not done with nested plates.

Agreed, I think most stamps of the era were two pass printings (hence stamps with misalignments/inverts).
Don

Two seperate passes with two different plates, one for the vignette and one for the frame.

Does it?
I would have thought only when gummed.
In wet printing, the paper I assume is only damp,
and could easily survive two passes.

Yes, I know they were made with two printing passes. My question was whether it was printed on 1) dry paper, 2) paper that was wetted, centers printed, dried, re-wetted, frames printed, or 3) paper wetted and both plates applied in quick succession. Sounds like #2 is the best bet so far.

(I just realized y'all have a sub-forum for questions about process; sorry I didn't see that in time.)

I just discovered the answer to my own question: in looking at the Pan-American Expo series, arrow blocks, there are the large arrows, which show both colors superimposed and _blended_. This could only happen if the paper stayed damp between impressings.