I agree with Elmer, wash the shell with some Dawn and let it air dry overnight, (don't let it sit out any longer, it'll only collect dust again), then paint it. If you're not going to paint it right away, put it in a plastic bag, (like a large Zip-Lock bag). to keep it dust free until you're ready.
Jay
C-415 Build: https://imageshack.com/a/tShC/1
Other builds: https://imageshack.com/my/albums
If there is dust on the shell, it means that you didn't pack it away so it wouldn't get dirty. In that case I would wash it with non-lotion dish detergent and let it dry for a few days. Better safe than sorry.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
Ok
I'm not an expert on this, but you should just need to wipe it. Most resin has a mold release agent on it that effects the paint adhesion. Whenever I work with resin I soak it in a mix of water and dish soap.
Disclaimer: I AM A TEENAGER!!!
Me
I primed a set of IHP Jersey Arrow lll's two years ago but never got to paint them. I've resurrected the project one again and I'm ready to paint them. Is it necessary to wash them once more again or should I simply wipe the primed shells from dust, dirt etc.