I've done some Cold Bluing and if you do the preparation carefully the results can look pretty good.

Preparation starts with wet sanding down to 1500 grit or finer followed up by a full polish. BTW, rub it down with motor oil between work sessions to provide a rust barrier. Then after the full polish you need to get the surface PERFECTLY clean of any trace of oil just before applying the bluing solution. Start with mineral spirits, then a bath in Dawn or Joy dish soap water, follow that with a bath in denatured alcohol, then air dry using a hair blower. Once dry apply the cold bluing and lightly rub the solution on the finish using gauze soaked with it. Once you see the solution starting to get milky and the finish not changing it's time for a good rinsing in distilled water. BTW, any water you use at all stages should be distilled. After the rinse then dry it off with some paper towels. Finally you then need to apply some plain old additive free oil such as Air Tool Oil or Hydraulic Oil. Don't miss any nooks or cranny's so a full dip isn't a bad idea. They you can wipe it all down with paper towels until it appears dry. After that you can then wax it with the wax of your choice, personally being a car nut I use Mothers Carnuba.

Granted, this won't match what can be done with the various hot bluing processes but if you are really careful about cleanliness and perfect preparation you will have a finish that looks pretty darned good. Note, you can purchase Latex or Vinyl gloves at any pharmacy so that will keep skin oils and crud off the finish. Also you really want a polish as near a mirror finish as you can achieve and you want it even as possible. This means a lot of hours (about 30) hand polishing with something like 3M Finnesite (about 50 bucks per quart but worth it).

Final note, Cold Bluing solution is the same as Black Oxide solution from an an industrial supply shop and the Black Oxide solution comes in larger bottles.