I use Blue Magic metal polish cream, as per directed. Typically applied with a polishing diaper and removed black leftover with blue shop paper towels (or anything else; just what I use). For threads I dampen the end of a q-tip with isopropyl alcohol (is that what you guys were calling ISO or is ISO some sort of cleaning agent

) and rub them good and make sure to remove any buildup or crud left from polishing.
Though recently bought a dremel for quicker work as I own several copper mods. It's a bit messier for the surrounding area (and I may have ruined a decent shirt

) I found in my first run around, so will probably be polishing mods either in garage or on front porch from now on.
Needless to say, I have been meaning to try ketchup as a polishing agent but what I have been using (the Blue Magic) has worked great for me so far so why change?