oil based ink on top of rubber based?

I made the mistake of printing with rubber based ink on top of an under layer of oil based ink. 5 days later, the rubber ink is still tacky. When the rubber based ink finally dries, I will need to overprint with 2 more colors. Will I get more rapid drying if I switch back to oil based inks for the remaining 2 press runs?

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Yes, use oil base ink for any additional press runs, not rubber base.

You want to keep in mind that rubber base ink “dries” mainly (and certainly most quickly) by being absorbed into the paper. (That’s why it’s not recommended for some coated or any non-absorbent stock.) Your first layer of oil base ink more-or-less sealed the paper preventing the rubber base from being effectively absorbed. Any further layers of rubber base ink will have the same drying problem, but perhaps even more so, as progressively less and less will be able to be absorbed by the paper.

Oil base ink dries by oxidation as well as absorption, so will dry on virtually any surface as long as it’s exposed to some air (not in a really tight stack, for instance). Of course, this is why oil base ink “skins” in the can, and it means you should be able to print additional colors on top of the rubber base (when it finally dries) with no problem and it should dry as quickly as it usually would on a relatively non-porus surface; but you may want to consider adding just a bit of drier to your ink if quick drying is needed.

Dave (the Ink in Tubes guy)