I've gotten reasonable results with cold blueing solutions on fixtures, jigs and tools by doing the following:
1. Metal prep. Polish to 400, then back down to 320. The quality of a blue job is directly connected to the quality of the metal prep. If you need to just remove a blue job without polishing it off, there are blue removers. Most of them contain phosphoric acid. A couple years ago, there was a toilet bowl cleaner that had a combination of phosphoric and muriatic acids. It stripped blue so fast, it had to be seen to be believed.
2. Completely de-grease/de-oil the metal. This is perhaps the most important step to getting an even blue. You can wash the metal in hot water with Dicro-clean 909, Du-Lite #37 or something similar, or you could use solutions of hot water with washing soda or lye, etc.
Brake cleaners work, as does acetone. I would strongly recommend you clean with these products outside.
3. After you're done cleaning the metal, you cannot handle it with your bare hands. Get some disposable nitrile gloves.
4. It helps to pre-warm the metal before applying the cold blue solution. You need to heat it up, and to do this you could put it in a clean hot water bath, or put it in an oven, warm it with a propane torch, etc.
5. You now apply the cold blue solution.
Please note: So far, everything we've done applies exactly the same to rust blueing. The only point where we diverge here is in the type of corrosive formula for oxidizing the steel. Cold blue solutions are more aggressive than rust blue solutions in that the rust blue solutions will cause red rust to form, and the red rust is converted to black rust when the item is put into clean boiling water. The cold blue solutions skip over the red rust step and try to jump directly to black rust.
6. In cold blueing, you won't have to wait for "fuzz" to form, nor will you need to convert red rust to black rust. What you will do in both types of blueing is "card" the steel. If we are rust blueing, then at this point the steel goes into a tank of boiling distilled water for 10 minutes.
7. Get some OIL FREE 0000 steel wool, and LIGHTLY rub down the blue job. You're not trying to scrub off the black oxide, you're simply trying to even up irregularities. If you have a slow speed grinder, you get get a 6" wire wheel of .005" wires to do your carding. This wire wheel should never be used for anything but carding during blueing. If it gets loaded up with any oil, you will have to clean it in the Dicro-clean or somehow else remove all the oil from the wheel.
Oil free steel wool is available through woodworker's supply companies, or you can de-oil your own steel wool by filling a coffee can with acetone, dunking the pad of steel wool and letting it then drain/dry.
7. If the metal has cooled off, you will want to re-warm it.
8. Apply a second coat of cold blue. Repeat the steps above. You might want to repeat up to, oh, four or five times. When I'm express or rust blueing, it might take as many as nine iterations to get the depth of blue that I would like. When I'm hot blueing, I might go back into the salts tank up to three times.
9. When you're satisfied with the quality of the blue, you need to rinse off any excess solution, no matter what method you're using. Usually this is done with clean boiling water.
10. You should then get some water displacing oil and either coat the part/gun with it, or if you have enough of the oil, just drop the gun in an oil bath for 30 minutes. Pull part/gun out and allow to oil to drain off, but DO NOT wipe it down. Leave the part/gun sit unmolested for 24+ hours to allow the oxide time to harden. The oiling and leaving it sit for 24 hours is what I do whether I'm hot blueing, rust blueing, cold blueing, whatever. I leave the blue layer sit without handling for a full day.
For the trouble I go through to blue anything, I'll usually go with the rust blueing process, even tho it might require the most iterations to get the depth of blue I like. I think the only process that's better than rust blueing is fume blueing. As long as you have a tank of sufficient size to hold your item in boiling water, you can rust blue. Many people could use a small rifle-length steel sheet metal tank on their kitchen stove to accomplish the boiling.
For people who have had blue "rub off" - this is a classic sign of incomplete degreasing. The reason I believe my cold blueing doesn't rub off my tooling and fixtures is because I degrease/de-oil my metal, even when the cold blue solution/glop says you "don't need to." I view any claims that no de-greasing is necessary, regardless of the blueing method, to be complete nonsense.
BTW, for those who wish to make a study of the topic, I recommend the following book:
"Firearm Blueing and Browning," by R.H. Angier, (c) 1936. Available from Stackpole Books.
Contained in this volume are a great number of formulas for blueing and browning chemicals, as well as other methods of metal surface treatment. Some of the chemistry in this book is dangerous, so if you've never handled caustic or acidic chemicals before, you might want to learn how to do that before experimenting with the contents of this book.
