I polish a lot of flat pieces and need to gwet the polish of the
edges and out of cracks also. What I use is a brass kitchen cleaning
brush. It does a good job getting into the cracks because it has
fine, stiff bristles. For some reason, the brass color does not seem
to wear off or come off on the polished surfaces. The only time I
have seen the brass bristle marks was on a piece of obsidian. You
might want to try one of these for cleaning.
One other thought. Use the polish (like cerium) verr, very sparingly.
You don’t need lots and lots on a good elk hide leather buff.