If you are able to make an RTV mold off of an original, then regular
terra cotta pottery clay or porcelain takes a really fine
fingerprint (you just want a really fine-grained clay).
I imagine Sculpey would work as well, just get it warm and kneaded
with your hands, talcum powder the tiny fingerprints (brush off
excess powder with a paint brush), and print. But then you have to
make an RTV mold of your original…