I polish to 320 grit, as going above that will not change the final finish. Actually, I go to 400 grit to be sure I have all of the 240 grit scratches out, then I sand with 320 for a second time. The mechanics of how rust blues work will make finer polishes look like 320. Also, I have had a hard time getting the solution to "bite" (start rusting) when going to higher finishes than 320.

skunk out