Regular moisture shouldn't cause a transfer. Lithographic inks are oil based so they won't be affected by moisture. Some sort of oil based solvent would be needed.
I've become extremely leery of transfers, especially any involving black ink. I recently bought a couple items- Card proofs of stamps from the 1880's- neither of them had any transfers. When they arrived from the UK having been shipped together in the same inner envelope the black one had left a very solid transfer on the other one. So the ink hadn't actually dried in roughly 130 years!
The printing process was different, but the ink used was also oil based. Lithography uses less ink than engraving, but all that will likely be needed to produce a transfer of a black back is pressure and a bit of time. And since the base of the inks is probably the same, it should work for other colors as well.
Steve B
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