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?
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