Could one capture grain from other the other grainy sources and lay it on top?
I’ve been wondering this myself. I know that it is possible to, when scanning a print, get the camera to only pick up dust, dirt, hairs, and scratches. I have absolutely zero knowledge as to how scanning works, but poita explained in this post:
Okay, there are a pair of TIFF files on the share that have the IR damage matte in the alpha channel if you’d like to take a look.
Anyone who wants to know what an Infr Red damage matte looks like…
The top image is what the film frame looks like under infra red light, the film is completely transparent to infra red, so the only thing the camera picks up is any dust, dirt, hairs or damage on the film.
The bottom image is the film frame the IR matte is taken from.
I am not sure if the grain could be picked up like this because it is so small and packed together, but having an extremely authentic layer of grain would, while mostly unnoticeable, be such a cool detail to make this feel even more polished.