Question about replicating a plaque with polymer clay

Our friend's small pet had to be euthanized while they were away. The vet gave us a little memorial plaque with the pet's footprints and name pressed into it. We want to send the plaque to the owners of the pet, but we'd like to replicate it first so that we may use the plaque as part of a gravestone. My question is, how do I best go about this without damaging the original in any way? The original appears to be made of polymer clay itself, though I can't be certain about that. I thought maybe I'd use the same color (terra cotta) polymer clay, press it in, pull it out and bake it, the repeat the process to get my copy. But I'm afraid to risk somehow messing up the original. Should I spray vegetable oil (or something) on the original first as a release agent? Or will that stain? Any help on this would be appreciated.