In my opinion most blueing looks better on polished metal. There are many brands of cold blueing and they all seem a little different in their final look(depending on prep,application,etc.).You can also get a great blue(s) just with heat.I have done this in a standard oven....though I can't recall the exact temperature(s) off the top of my head.If I were to try this myself,I would wire brush as you described,then heat to the blue I wanted. Finally,I would mask the blue that I wanted to keep and wire brush again to remove the blueing in areas I did not want blue.I think the same could be done with cold blueing as well,but it may be a bit tougher than the heat blue to remove.