That's an excellent question Tim, because with bluing particularly, you must card the steel removing scale that accumulates during the browning process. The carding on this piece was done using Brownell's soft wire wheel at 500 rpm. In short, the finish is more IN the steel than ON it. So, unless you remove file marks etc, they will show up after the boiling and carding is done.
So, the long answer is, I draw file to remove casting marks and to finalize the shape, and then use progressively finer abrasive cloth and paper, backed with various items including dowels, files, rubber hose, and special cut pieces of rubber from a found engine support block. I likely stopped at 400 - 600 on this piece. So the sequence would have been file, then abrasives 80, 120, 180, 220, 320, 400, and 600. I use some wet/dry paper but I also use Norton's sandpaper...cuts nicely and lasts well. When polishing steel, you will find that each finer grade of abrasive takes less time than the previous. On each successive grade, I change the polish angle so that I can clearly see that I have removed the marks left by the coarser paper/cloth, ending with lengthwise stokes of the finest.
All the screw heads are engraved, case hardened and burnished with a wire wheel.